Internet DRAFT - draft-ietf-rift-rift
draft-ietf-rift-rift
RIFT Working Group A. Przygienda, Ed.
Internet-Draft J. Head, Ed.
Intended status: Standards Track Juniper Networks
Expires: 22 August 2024 P. Thubert
Cisco
Bruno. Rijsman
Individual
Dmitry. Afanasiev
Yandex
19 February 2024
RIFT: Routing in Fat Trees
draft-ietf-rift-rift-20
Abstract
This document defines a specialized, dynamic routing protocol for
Clos and fat tree network topologies optimized towards minimization
of control plane state as well as minimization of configuration and
operational complexity.
Status of This Memo
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Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 7
2. A Reader's Digest . . . . . . . . . . . . . . . . . . . . . . 7
3. Reference Frame . . . . . . . . . . . . . . . . . . . . . . . 10
3.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 10
3.2. Topology . . . . . . . . . . . . . . . . . . . . . . . . 16
4. RIFT: Routing in Fat Trees . . . . . . . . . . . . . . . . . 19
5. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.1. Properties . . . . . . . . . . . . . . . . . . . . . . . 19
5.2. Generalized Topology View . . . . . . . . . . . . . . . . 20
5.2.1. Terminology and Glossary . . . . . . . . . . . . . . 20
5.2.2. Clos as Crossed, Stacked Crossbars . . . . . . . . . 21
5.3. Fallen Leaf Problem . . . . . . . . . . . . . . . . . . . 31
5.4. Discovering Fallen Leaves . . . . . . . . . . . . . . . . 33
5.5. Addressing the Fallen Leaves Problem . . . . . . . . . . 34
6. Specification . . . . . . . . . . . . . . . . . . . . . . . . 35
6.1. Transport . . . . . . . . . . . . . . . . . . . . . . . . 36
6.2. Link (Neighbor) Discovery (LIE Exchange) . . . . . . . . 36
6.2.1. LIE Finite State Machine . . . . . . . . . . . . . . 42
6.3. Topology Exchange (TIE Exchange) . . . . . . . . . . . . 52
6.3.1. Topology Information Elements . . . . . . . . . . . . 52
6.3.2. Southbound and Northbound TIE Representation . . . . 53
6.3.3. Flooding . . . . . . . . . . . . . . . . . . . . . . 56
6.3.4. TIE Flooding Scopes . . . . . . . . . . . . . . . . . 65
6.3.5. RAIN: RIFT Adjacency Inrush Notification . . . . . . 70
6.3.6. Initial and Periodic Database Synchronization . . . . 70
6.3.7. Purging and Roll-Overs . . . . . . . . . . . . . . . 70
6.3.8. Southbound Default Route Origination . . . . . . . . 71
6.3.9. Northbound TIE Flooding Reduction . . . . . . . . . . 72
6.3.10. Special Considerations . . . . . . . . . . . . . . . 77
6.4. Reachability Computation . . . . . . . . . . . . . . . . 78
6.4.1. Northbound Reachability SPF . . . . . . . . . . . . . 79
6.4.2. Southbound Reachability SPF . . . . . . . . . . . . . 80
6.4.3. East-West Forwarding Within a non-ToF Level . . . . . 80
6.4.4. East-West Links Within ToF Level . . . . . . . . . . 80
6.5. Automatic Disaggregation on Link & Node Failures . . . . 80
6.5.1. Positive, Non-transitive Disaggregation . . . . . . . 80
6.5.2. Negative, Transitive Disaggregation for Fallen
Leaves . . . . . . . . . . . . . . . . . . . . . . . 84
6.6. Attaching Prefixes . . . . . . . . . . . . . . . . . . . 86
6.7. Optional Zero Touch Provisioning (ZTP) . . . . . . . . . 94
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6.7.1. Terminology . . . . . . . . . . . . . . . . . . . . . 95
6.7.2. Automatic System ID Selection . . . . . . . . . . . . 97
6.7.3. Generic Fabric Example . . . . . . . . . . . . . . . 97
6.7.4. Level Determination Procedure . . . . . . . . . . . . 98
6.7.5. ZTP FSM . . . . . . . . . . . . . . . . . . . . . . . 100
6.7.6. Resulting Topologies . . . . . . . . . . . . . . . . 105
6.8. Further Mechanisms . . . . . . . . . . . . . . . . . . . 106
6.8.1. Route Preferences . . . . . . . . . . . . . . . . . . 106
6.8.2. Overload Bit . . . . . . . . . . . . . . . . . . . . 107
6.8.3. Optimized Route Computation on Leaves . . . . . . . . 107
6.8.4. Mobility . . . . . . . . . . . . . . . . . . . . . . 108
6.8.5. Key/Value (KV) Store . . . . . . . . . . . . . . . . 111
6.8.6. Interactions with BFD . . . . . . . . . . . . . . . . 112
6.8.7. Fabric Bandwidth Balancing . . . . . . . . . . . . . 113
6.8.8. Label Binding . . . . . . . . . . . . . . . . . . . . 116
6.8.9. Leaf to Leaf Procedures . . . . . . . . . . . . . . . 116
6.8.10. Address Family and Multi Topology Considerations . . 117
6.8.11. One-Hop Healing of Levels with East-West Links . . . 117
6.9. Security . . . . . . . . . . . . . . . . . . . . . . . . 117
6.9.1. Security Model . . . . . . . . . . . . . . . . . . . 117
6.9.2. Security Mechanisms . . . . . . . . . . . . . . . . . 119
6.9.3. Security Envelope . . . . . . . . . . . . . . . . . . 120
6.9.4. Weak Nonces . . . . . . . . . . . . . . . . . . . . . 123
6.9.5. Lifetime . . . . . . . . . . . . . . . . . . . . . . 124
6.9.6. Security Association Changes . . . . . . . . . . . . 125
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 125
7.1. Normal Operation . . . . . . . . . . . . . . . . . . . . 125
7.2. Leaf Link Failure . . . . . . . . . . . . . . . . . . . . 127
7.3. Partitioned Fabric . . . . . . . . . . . . . . . . . . . 128
7.4. Northbound Partitioned Router and Optional East-West
Links . . . . . . . . . . . . . . . . . . . . . . . . . . 129
8. Further Details on Implementation . . . . . . . . . . . . . . 130
8.1. Considerations for Leaf-Only Implementation . . . . . . . 130
8.2. Considerations for Spine Implementation . . . . . . . . . 131
9. Security Considerations . . . . . . . . . . . . . . . . . . . 131
9.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 131
9.2. Time to Live and Hop Limit Values . . . . . . . . . . . . 131
9.3. Malformed Packets . . . . . . . . . . . . . . . . . . . . 132
9.4. ZTP . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
9.5. Lifetime . . . . . . . . . . . . . . . . . . . . . . . . 132
9.6. Packet Number . . . . . . . . . . . . . . . . . . . . . . 133
9.7. Outer Fingerprint Attacks . . . . . . . . . . . . . . . . 133
9.8. TIE Origin Fingerprint DoS Attacks . . . . . . . . . . . 133
9.9. Host Implementations . . . . . . . . . . . . . . . . . . 134
9.9.1. IPv4 Broadcast and IPv6 All Routers Multicast
Implementations . . . . . . . . . . . . . . . . . . . 134
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 134
10.1. Requested Multicast and Port Numbers . . . . . . . . . . 135
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10.2. Requested Registries with Assigned Values . . . . . . . 135
10.2.1. Expert Review Guidance . . . . . . . . . . . . . . . 135
10.2.2. Registry RIFT/Versions . . . . . . . . . . . . . . . 136
10.2.3. Registry RIFT/common/AddressFamilyType . . . . . . . 136
10.2.4. Registry RIFT/common/HierarchyIndications . . . . . 137
10.2.5. Registry RIFT/common/IEEE802_1ASTimeStampType . . . 138
10.2.6. Registry RIFT/common/IPAddressType . . . . . . . . . 138
10.2.7. Registry RIFT/common/IPPrefixType . . . . . . . . . 139
10.2.8. Registry RIFT/common/IPv4PrefixType . . . . . . . . 140
10.2.9. Registry RIFT/common/IPv6PrefixType . . . . . . . . 140
10.2.10. Registry RIFT/common/KVTypes . . . . . . . . . . . . 141
10.2.11. Registry RIFT/common/PrefixSequenceType . . . . . . 141
10.2.12. Registry RIFT/common/RouteType . . . . . . . . . . . 142
10.2.13. Registry RIFT/common/TIETypeType . . . . . . . . . . 143
10.2.14. Registry RIFT/common/TieDirectionType . . . . . . . 144
10.2.15. Registry RIFT/encoding/Community . . . . . . . . . . 145
10.2.16. Registry RIFT/encoding/KeyValueTIEElement . . . . . 146
10.2.17. Registry RIFT/encoding/KeyValueTIEElementContent . . 146
10.2.18. Registry RIFT/encoding/LIEPacket . . . . . . . . . . 147
10.2.19. Registry RIFT/encoding/LinkCapabilities . . . . . . 150
10.2.20. Registry RIFT/encoding/LinkIDPair . . . . . . . . . 151
10.2.21. Registry RIFT/encoding/Neighbor . . . . . . . . . . 152
10.2.22. Registry RIFT/encoding/NodeCapabilities . . . . . . 153
10.2.23. Registry RIFT/encoding/NodeFlags . . . . . . . . . . 154
10.2.24. Registry RIFT/encoding/NodeNeighborsTIEElement . . . 155
10.2.25. Registry RIFT/encoding/NodeTIEElement . . . . . . . 156
10.2.26. Registry RIFT/encoding/PacketContent . . . . . . . . 158
10.2.27. Registry RIFT/encoding/PacketHeader . . . . . . . . 158
10.2.28. Registry RIFT/encoding/PrefixAttributes . . . . . . 159
10.2.29. Registry RIFT/encoding/PrefixTIEElement . . . . . . 160
10.2.30. Registry RIFT/encoding/ProtocolPacket . . . . . . . 161
10.2.31. Registry RIFT/encoding/TIDEPacket . . . . . . . . . 162
10.2.32. Registry RIFT/encoding/TIEElement . . . . . . . . . 163
10.2.33. Registry RIFT/encoding/TIEHeader . . . . . . . . . . 163
10.2.34. Registry RIFT/encoding/TIEHeaderWithLifeTime . . . . 164
10.2.35. Registry RIFT/encoding/TIEID . . . . . . . . . . . . 165
10.2.36. Registry RIFT/encoding/TIEPacket . . . . . . . . . . 166
10.2.37. Registry RIFT/encoding/TIREPacket . . . . . . . . . 167
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 167
12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 168
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 168
13.1. Normative References . . . . . . . . . . . . . . . . . . 168
13.2. Informative References . . . . . . . . . . . . . . . . . 170
Appendix A. Sequence Number Binary Arithmetic . . . . . . . . . 172
Appendix B. Information Elements Schema . . . . . . . . . . . . 173
B.1. Backwards-Compatible Extension of Schema . . . . . . . . 174
B.2. common.thrift . . . . . . . . . . . . . . . . . . . . . . 175
B.3. encoding.thrift . . . . . . . . . . . . . . . . . . . . . 181
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 188
1. Introduction
Clos [CLOS] topologies (called commonly a fat tree/network in modern
IP fabric considerations [VAHDAT08] as homonym to the original
definition of the term [FATTREE]) have gained prominence in today's
networking, primarily as a result of the paradigm shift towards a
centralized data-center architecture that is poised to deliver a
majority of computation and storage services in the future. Many
builders of such IP fabrics desire a protocol that auto-configures
itself and deals with failures and mis-configurations with a minimum
of human intervention. Such a solution would allow local IP fabric
bandwidth to be consumed in a 'standard component' fashion, i.e.
provision it much faster and operate it at much lower costs than
today, much like compute or storage is consumed already.
In looking at the problem through the lens of such IP fabric
requirements, RIFT (Routing in Fat Trees) addresses those challenges
not through an incremental modification of either a link-state
(distributed computation) or distance-vector (diffused computation)
techniques but rather a mixture of both, briefly described as "link-
state towards the spines" and "distance vector towards the leaves".
In other words, "bottom" levels are flooding their link-state
information in the "northern" direction while each node generates
under normal conditions a "default route" and floods it in the
"southern" direction. This type of protocol allows naturally for
highly desirable address aggregation. Alas, such aggregation could
drop traffic in cases of misconfiguration or while failures are being
resolved or even cause persistent network partitioning and this has
to be addressed by some adequate mechanism. The approach RIFT takes
is described in Section 6.5 and is based on automatic, sufficient
disaggregation of prefixes in case of link and node failures.
The protocol does further provide:
* optional fully automated construction of fat tree topologies based
on detection of links without any configuration (Section 6.7),
while allowing for conventional configuration methods or an
arbitrary mix of both,
* minimum amount of routing state held by nodes,
* automatic pruning and load balancing of topology flooding
exchanges over a sufficient subset of links (Section 6.3.9),
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* automatic address aggregation (Section 6.3.8) and consequently
automatic disaggregation (Section 6.5) of prefixes on link and
node failures to prevent traffic loss and suboptimal routing,
* loop-free non-ECMP forwarding due to its inherent valley-free
nature,
* fast mobility (Section 6.8.4),
* re-balancing of traffic towards the spines based on bandwidth
available (Section 6.8.7.1), and finally
* mechanisms to synchronize a limited key-value data-store
(Section 6.8.5.1) that can be used after protocol convergence to
e.g. bootstrap higher levels of functionality on nodes.
Figure 1 illustrates a simplified, conceptual view of a RIFT fabric
with its routing tables and topology databases. The top of the
fabric's link-state database holds information about the nodes below
it and the routes to them. When referring to Figure 1, the /32
notation corresponds to each node's loopback address (e.g. A/32 is
node A's loopback, etc.) and 0/0 indicates a default route. The
first row of database information represents the nodes for which full
topology information is available. The second row of database
information indicates that partial information of other nodes in the
same level is also available. Such information will be necessary to
perform certain algorithms necessary for correct protocol operation.
When the "bottom" of the fabric is considered, or in other words the
leaves, the topology is basically empty and, under normal conditions,
the leaves hold a load balanced default route to the next level.
The remainder of this document fills in the protocol specification
details.
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[A,B,C,D]
[E]
+---------+ +---------+ A/32 @ [C,D]
| E | | F | B/32 @ [C,D]
+-+-----+-+ +-+-----+-+ C/32 @ C
| | | | D/32 @ D
| | | |
| | +--+ |
| | | |
| +---------)--+ |
| | | |
| | | |
| +---------+ | |
| | | |
[A,B] +-+-----+-+ +-+-----+-+ [A,B]
[D] | C | | D | [C]
+-+-----+-+ +-+-----+-+
0/0 @ [E,F] | | | | 0/0 @ [E,F]
A/32 @ [A] | | | | A/32 @ A
B/32 @ [B] | | +--+ | B/32 @ B
| | | |
| +---------)--+ |
| | | |
| +---------+ | |
| | | |
+-+-----+-+ +-+-----+-+
0/0 @ [C,D] | A | | B | 0/0 @ [C,D]
+---------+ +---------+
Figure 1: RIFT Information Distribution
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. A Reader's Digest
This section is an initial guided tour through the document in order
to convey the necessary information for different readers, depending
on their level of interest. The authors recommend reading the HTML
or PDF versions of this document due to the inherent limitation of
text version to represent complex figures.
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The Terminology (Section 3.1) section should be used as a supporting
reference as the document is read.
The indications of direction (i.e. "top", "bottom", etc.) referenced
in Section 1 are of paramount importance. RIFT requires a topology
with a sense of top and bottom in order to properly achieve a sorted
topology. Clos, Fat Tree, and other similarly structured networks
are conducive to such requirements. Where RIFT does allow for
further relaxation of these constraints, this will be mentioned later
in this section.
Several of the images in this document are annotated with "northern
view" or "southern view" to indicate perspective to the reader. A
"northern view" should be interpreted as "from the top of the fabric
looking down", whereas "southern view" should be interpreted as "from
the bottom looking up".
Operators and implementors alike must decide whether multi-plane IP
fabrics are of interest for them. Section 3.2 illustrates an example
of both single-plane in Figure 2 and multi-plane fabric in Figure 3.
Multi-plane fabrics require understanding of additional RIFT concepts
(e.g. negative disaggregation in Section 6.5.2) that are unnecessary
in the context of fabrics consisting of a single-plane only. The
Overview (Section 5) and Section 5.2 aim to provide enough context to
determine if multi-plane fabrics are of interest to the reader. The
Fallen Leaf part (Section 5.3), and additionally Section 5.4 and
Section 5.5 describe further considerations that are specific to
multi-plane fabrics.
The fundamental protocol concepts are described starting in the
specification part (Section 6), but some sub-sections are less
relevant unless the protocol is being implemented. The protocol
transport (Section 6.1) is of particular importance for two reasons.
First, it introduces RIFT's packet format content in the form of a
normative Thrift model given in Appendix B.3 carried in according
security envelope as described in Section 6.9.3. Second, the Thrift
model component is a prelude to understanding the RIFT's inherent
security features as defined in both security models part
(Section 6.9) and the security segment (Section 9). The normative
schema defining the Thrift model can be found in Appendix B.2 and
Appendix B.3. Furthermore, while a detailed understanding of Thrift
[thrift] and the models is not required unless implementing RIFT,
they may provide additional useful information for other readers.
If implementing RIFT to support multi-plane topologies Section 6
should be reviewed in its entirety in conjunction with the previously
mentioned Thrift schemas. Sections not relevant to single-plane
implementations will be noted later in this section.
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All readers dealing with implementation of the protocol should pay
special attention to the Link Information Element (LIE) definitions
part (Section 6.2) as it not only outlines basic neighbor discovery
and adjacency formation, but also provides necessary context for
RIFT's Zero Touch Provisioning (ZTP) (Section 6.7) and mis-cabling
detection capabilities that allow it to automatically detect and
build the underlay topology with basically no configuration. These
specific capabilities are detailed in Section 6.7.
For other readers, the following sections provide a more detailed
understanding of the fundamental properties and highlight some
additional benefits of RIFT such as link state packet formats,
efficient flooding, synchronization, loop-free path computation and
link-state database maintenance - Section 6.3, Section 6.3.2,
Section 6.3.3, Section 6.3.4, Section 6.3.6, Section 6.3.7,
Section 6.3.8, Section 6.4, Section 6.4.1, Section 6.4.2,
Section 6.4.3, Section 6.4.4. RIFT's ability to perform weighted
unequal-cost load balancing of traffic across all available links is
outlined in Section 6.8.7 with an accompanying example.
Section 6.5 is the place where the single-plane vs. multi-plane
requirement is explained in more detail. For those interested in
single-plane fabrics, only Section 6.5.1 is required. For the multi-
plane interested reader Section 6.5.2, Section 6.5.2.1,
Section 6.5.2.2, and Section 6.5.2.3 are also mandatory. Section 6.6
is especially important for any multi-plane interested reader as it
outlines how the RIB (Routing Information Base) and FIB (Forwarding
Information Base) are built via the disaggregation mechanisms, but
also illustrates how they prevent defective routing decisions that
cause traffic loss in both single or multi-plane topologies.
Section 7 contains a set of comprehensive examples that show how RIFT
contains the impact of failures to only the required set of nodes.
It should also help cement some of RIFT's core concepts in the
reader's mind.
Last, but not least, RIFT has other optional capabilities. One
example is the key-value data-store, which enables RIFT to advertise
data post-convergence in order to bootstrap higher levels of
functionality (e.g. operational telemetry). Those are covered in
Section 6.8.
More information related to RIFT can be found in the "RIFT
Applicability" [APPLICABILITY] document, which discusses alternate
topologies upon which RIFT may be deployed, use cases where it is
applicable, and presents operational considerations that complement
this document. The RIFT DayOne [DayOne] book covers some practical
details of existing RIFT implementations.
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3. Reference Frame
3.1. Terminology
This section presents the terminology used in this document.
Bandwidth Adjusted Distance (BAD):
Each RIFT node can calculate the amount of northbound bandwidth
available towards a node compared to other nodes at the same level
and can modify the route distance accordingly to allow for the
lower level to adjust their load balancing towards spines.
Bi-directional Adjacency:
Bidirectional adjacency is an adjacency where nodes of both sides
of the adjacency advertised it in the Node TIEs with the correct
levels and System IDs. Bi-directionality is used to check in
different algorithms whether the link should be included.
Bow-tying:
Traffic patterns in fully converged IP fabrics traverse normally
the shortest route based on hop count toward their destination
(e.g., leaf, spine, leaf). Some failure scenarios with partial
routing information cause nodes to lose the required downstream
reachability to a destination and forcing traffic to utilize
routes that traverse higher levels in the fabric in order to turn
south again using a different to resolve reachability (e.g., leaf,
spine-1, super-spine, spine-2, leaf).
Clos/Fat Tree:
This document uses the terms Clos and Fat Tree interchangeably
where it always refers to a folded spine-and-leaf topology with
possibly multiple Points of Delivery (PoDs) and one or multiple
Top of Fabric (ToF) planes. Several modifications such as leaf-
2-leaf shortcuts and multiple level shortcuts are possible and
described further in the document.
Cost:
The sum of metrics between two nodes.
Crossbar:
Physical arrangement of ports in a switching matrix without
implying any further scheduling or buffering disciplines.
Directed Acyclic Graph (DAG):
A finite directed graph with no directed cycles (loops). If links
in a Clos are considered as either being all directed towards the
top or vice versa, each of such two graphs is a DAG.
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Disaggregation:
Process in which a node decides to advertise more specific
prefixes Southwards, either positively to attract the
corresponding traffic, or negatively to repel it. Disaggregation
is performed to prevent traffic loss and suboptimal routing to the
more specific prefixes.
Distance:
The sum of costs (bound by infinite distance) between two nodes.
East-West (E-W) Link:
A link between two nodes at the same level. East-West links are
normally not part of Clos or "fat tree" topologies.
Flood Repeater (FR):
A node can designate one or more northbound neighbor nodes to be
flood repeaters. The flood repeaters are responsible for flooding
northbound TIEs further north. The document sometimes calls them
flood leaders as well.
Folded Spine-and-Leaf:
In case the Clos fabric input and output stages are analogous, the
fabric can be "folded" to build a "superspine" or top which is
called the ToF in this document.
Interface:
A layer 3 entity over which RIFT control packets are exchanged.
Key Value (KV) TIE:
A TIE that is carrying a set of key value pairs [DYNAMO]. It can
be used to distribute non topology related information within the
protocol.
Leaf-to-Leaf Shortcuts (L2L):
East-West links at leaf level will need to be differentiated from
East-West links at other levels.
Leaf:
A node without southbound adjacencies. Level 0 implies a leaf in
RIFT but a leaf does not have to be level 0.
Level:
Clos and Fat Tree networks are topologically partially ordered
graphs and 'level' denotes the set of nodes at the same height in
such a network. Nodes at the top level (i.e., ToF) are at the
level with the highest value and count down to the nodes at the
bottom level (i.e., leaf) with the lowest value. A node will have
links to nodes one level down and/or one level up. In some
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circumstances, a node may have links to other nodes at the same
level. A leaf node may also have links to nodes multiple levels
higher. In RIFT, Level 0 always indicates that a node is a leaf,
but does not have to be level 0. Level values can be configured
manually or automatically derived via Section 6.7. As a final
footnote: Clos terminology often uses the concept of "stage", but
due to the folded nature of the Fat Tree it is not used from this
point on to prevent misunderstandings.
LIE:
This is an acronym for a "Link Information Element" exchanged on
all the system's links running RIFT to form _ThreeWay_ adjacencies
and carry information used to perform Zero Touch Provisioning
(ZTP) of levels.
Metric:
The cost between two neighbors exactly one layer 3 hop away from
each other.
Neighbor:
Once a _ThreeWay_ adjacency has been formed a neighborship
relationship contains the neighbor's properties. Multiple
adjacencies can be formed to a remote node via parallel point-to-
point interfaces but such adjacencies are *not* sharing a neighbor
structure. Saying "neighbor" is thus equivalent to saying "a
_ThreeWay_ adjacency".
Node TIE:
This stands as acronym for a "Node Topology Information Element",
which contains all adjacencies the node discovered and information
about the node itself. Node TIE should not be confused with a
North TIE since "node" defines the type of TIE rather than its
direction. Consequently North Node TIEs and South Node TIEs
exist.
North Radix:
The number of ports cabled northbound to higher level nodes.
North SPF (N-SPF):
A reachability calculation that is progressing northbound, as
example SPF that is using South Node TIEs only. Normally it
progresses a single hop only and installs default routes.
Northbound Link:
A link to a node one level up or in other words, one level further
north.
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Northbound representation:
Subset of topology information flooded towards higher levels of
the fabric.
Overloaded:
Applies to a node advertising the _overload_ attribute as set.
Overload attribute is carried in the _NodeFlags_ object of the
encoding schema.
Point of Delivery (PoD):
A self-contained vertical slice or subset of a Clos or Fat Tree
network containing normally only level 0 and level 1 nodes. A
node in a PoD communicates with nodes in other PoDs via the ToF
nodes. PoDs are numbered to distinguish them and PoD value 0
(defined later in the encoding schema as _common.default_pod_) is
used to denote "undefined" or "any" PoD.
Prefix TIE:
This is an acronym for a "Prefix Topology Information Element" and
it contains all prefixes directly attached to this node in case of
a North TIE and in case of South TIE the necessary default routes
the node advertises southbound.
Radix:
A radix of a switch is number of switching ports it provides.
It's sometimes called fanout as well.
Routing on the Host (RotH):
Modern data center architecture variant where servers/leaves are
multi-homed and consequently participate in routing.
Security Envelope:
RIFT packets are flooded within an authenticated security envelope
that allows to protect the integrity of information a node
accepts. This is described in Section 6.9.3.
Shortest-Path First (SPF):
A well-known graph algorithm attributed to Dijkstra [DIJKSTRA]
that establishes a tree of shortest paths from a source to
destinations on the graph. SPF acronym is used due to its
familiarity as general term for the node reachability calculations
RIFT can employ to ultimately calculate routes of which Dijkstra
algorithm is a possible one.
South Radix:
The number of ports cabled southbound to lower-level nodes.
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South Reflection:
Often abbreviated just as "reflection", it defines a mechanism
where South Node TIEs are "reflected" from the level south back up
north to allow nodes in the same level without E-W links to be
aware of each other's node Topology Information Elements (TIEs).
South SPF (S-SPF):
A reachability calculation that is progressing southbound, as
example SPF that is using North Node TIEs only.
South/Southbound and North/Northbound (Direction):
When describing protocol elements and procedures, in different
situations the directionality of the compass is used. i.e.,
'lower', 'south' or 'southbound' mean moving towards the bottom of
the Clos or Fat Tree network and 'higher', 'north' and
'northbound' mean moving towards the top of the Clos or Fat Tree
network.
Southbound Link:
A link to a node one level down or in other words, one level
further south.
Southbound representation:
Subset of topology information sent towards a lower level.
Spine:
Any nodes north of leaves and south of ToF nodes. Multiple layers
of spines in a PoD are possible.
Superspine, Aggregation/Spine and Edge/Leaf Switches:"
Traditional level names in 5-stages folded Clos for Level 2, 1 and
0 respectively (counting up from the bottom). We normalize this
language to talk about ToF, Top-of-Pod (ToP) and leaves.
System ID:
RIFT nodes identify themselves with a unique network-wide number
when trying to build adjacencies or describe their topology. RIFT
System IDs can be auto-derived or configured.
ThreeWay Adjacency:
RIFT tries to form a unique adjacency between two nodes over a
point-to-point interface and exchange local configuration and
necessary ZTP information. An adjacency is only advertised in
Node TIEs and used for computations after it achieved _ThreeWay_
state, i.e. both routers reflected each other in LIEs including
relevant security information. Nevertheless, LIEs before
_ThreeWay_ state is reached may carry ZTP related information
already.
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TIDE:
Topology Information Description Element carrying descriptors of
the TIEs stored in the node.
TIE:
This is an acronym for a "Topology Information Element". TIEs are
exchanged between RIFT nodes to describe parts of a network such
as links and address prefixes. A TIE has always a direction and a
type. North TIEs (sometimes abbreviated as N-TIEs) are used when
dealing with TIEs in the northbound representation and South-TIEs
(sometimes abbreviated as S-TIEs) for the southbound equivalent.
TIEs have different types such as node and prefix TIEs.
TIEDB:
The database holding the newest versions of all TIE headers (and
the corresponding TIE content if it is available).
TIRE:
Topology Information Request Element carrying set of TIDE
descriptors. It can both confirm received and request missing
TIEs.
Top of Fabric (ToF):
The set of nodes that provide inter-PoD communication and have no
northbound adjacencies, i.e. are at the "very top" of the fabric.
ToF nodes do not belong to any PoD and are assigned
_common.default_pod_ PoD value to indicate the equivalent of "any"
PoD.
Top of PoD (ToP):
The set of nodes that provide intra-PoD communication and have
northbound adjacencies outside of the PoD, i.e. are at the "top"
of the PoD.
ToF Plane or Partition:
In large fabrics ToF switches may not have enough ports to
aggregate all switches south of them and with that, the ToF is
'split' into multiple independent planes. Section 5.2 explains
the concept in more detail. A plane is a subset of ToF nodes that
are aware of each other through south reflection or E-W links.
Valid LIE:
LIEs undergo different checks to determine their validity. The
term "valid LIE" is used to describe a LIE that can be used to
form or maintain an adjacency. The amount of checking itself
depends on the FSM (Finite State Machine) involved and its state.
A "minimally valid LIE" is a LIE that passes checks necessary on
any FSM in any state. A "ThreeWay valid LIE" is a LIE that
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successfully underwent further checks with a LIE FSM in _ThreeWay_
state. Minimally valid LIE is a subcategory of _ThreeWay_ valid
LIE.
Zero Touch Provisioning (ZTP):
Optional RIFT mechanism which allows the automatic derivation of
node levels based on minimum configuration. Such a mininum
configuration consists solely of ToFs being configured as such.
Additionally, when the specification refers to elements of packet
encoding or constants provided in the Appendix B a special emphasis
is used, e.g. _invalid_distance_. The same convention is used when
referring to finite state machine states or events outside the
context of the machine itself, e.g., _OneWay_.
3.2. Topology
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^ N +--------+ +--------+
Level 2 | |ToF 21| |ToF 22|
W <-*-> E ++-+--+-++ ++-+--+-++
| | | | | | | | |
S v P111/2 P121/2 | | | |
^ ^ ^ ^ | | | |
| | | | | | | |
+--------------+ | +-----------+ | | | +---------------+
| | | | | | | |
South +-----------------------------+ | | ^
| | | | | | | All
0/0 0/0 0/0 +-----------------------------+ TIEs
v v v | | | | |
| | +-+ +<-0/0----------+ | |
| | | | | | | |
+-+----++ optional +-+----++ ++----+-+ ++-----++
Level 1 | | E/W link | | | | | |
|Spin111+----------+Spin112| |Spin121| |Spin122|
+-+---+-+ ++----+-+ +-+---+-+ ++---+--+
| | | South | | | |
| +---0/0--->-----+ 0/0 | +----------------+ |
0/0 | | | | | | |
| +---<-0/0-----+ | v | +--------------+ | |
v | | | | | | |
+-+---+-+ +--+--+-+ +-+---+-+ +---+-+-+
Level 0 | | (L2L) | | | | | |
|Leaf111+~~~~~~~~~~+Leaf112| |Leaf121| |Leaf122|
+-+-----+ +-+---+-+ +--+--+-+ +-+-----+
+ + \ / + +
Prefix111 Prefix112 \ / Prefix121 Prefix122
multi-homed
Prefix
+---------- PoD 1 ---------+ +---------- PoD 2 ---------+
Figure 2: A Three Level Spine-and-Leaf Topology
____________________________________________________________________________
| [Plane A] . [Plane B] . [Plane C] . [Plane D] |
|..........................................................................|
| +-+ . +-+ . +-+ . +-+ |
| |n| . |n| . |n| . |n| |
| +++ . +++ . +++ . +++ |
| . | | . . | | . . | | . . | | |
| . | | . . | | . . | | . . | | |
| +-+ | | . +-+ | | . +-+ | | . +-+ | | |
| |1| +-+ | . |1| +-+ | . |1| +-+ | . |1| +-+ | |
| +++ | | . +++ | | . +++ | | . +++ | | |
| || | | . || | | . || | | . || | | |
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| || | | . || | | . || | | . || | | |
| |+--|--+| . |+--|--+| . |+--|--+| . |+--|----+ |
| | | || . | | || . | | || . | | || |
| | | || . | | || . | | || . | | +|---+ |
=====|===|==||=========|===|==||=========|===|==||=========|===|====|===|=== |
/ | | | || . | | || . | | || . | | / | | / |
/ | | | || . | | || . | | || . | | / ++---++ / |
/ | | | || . | | || . | | || . | | / | n | / |
/ | | | || . | | || . | | || . | | / +++-+++ / |
/ | ++---++ || . ++---++ || . ++---++ || . ++---++/ / |
/ | | 1 | || . | 2 | || . | 3 | || . | 4 |/ / |
/ | +++-+++ || . +++-+++ || . +++-+++ || . +++-+++/ / |
/ | || || || . || || || . || || || . || || / / |
/ \__||_||_____________||_||_____________||_||_____________||_||_/_________/_/
/ || || || || || || || || / || || /
/ || || +-----------+| || || || || || / || || /
/ || || |+-----------|-||-------------+| || || || / || || /
/ || || ||+----------|-||--------------|-||-------------+| || / || || /
/ || || ||| | || | || +-------+ || / || || /
/ || || ||| | |+--------------|-||------|---+ || / || || /
/ || || ||| | | | || | | +-+| / || || /
/ || || ||| | +-----------+ | || | | | | / || || /
/ || +|-|||----------|------------+| | |+------|---|---|-+| / || || /
/ || +-|||----------|------------||---|-|-------|-+ | | || / || || /
/ || ||| | +------||---+ | | | | | || / || || /
/ |+----|||-----+ | |+-----||-----|-------+ | | | || / || || /
/ | ||| | | || || | | | | || / || || /
/ | ||| | | || || | +----|-|---+ || / || || /
/ | ||| | | || || | | | | || / || || /
/ |+----+|| | | || || | | | | || / || || /
/ || +---+| | | +---+| |+---+ | | | +---+ || / +++-+++ /
/ || |+---+ +---+| |+---+ +---+| |+---+ +----+| || / | n | /
/ || || || || || || || || / +++-+++ /
/ +++-+++ +++-+++ +++-+++ +++-+++/=========/
/ | 1 | | 2 + | 3 | . . . | n |/ ^^
/ +++-+++ +-----+ +-----+ +-----+/ //
/ / PoDs
================================================================== //
Figure 3: Topology with Multiple Planes
The topology in Figure 2 is referred to in all further
considerations. This figure depicts a generic "single plane fat
tree" and the concepts explained using three levels apply by
induction to further levels and higher degrees of connectivity.
Further, this document will deal also with designs that provide only
sparser connectivity and "partitioned spines" as shown in Figure 3
and explained further in Section 5.2.
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4. RIFT: Routing in Fat Trees
The remainder of this document presents the detailed specification of
the RIFT protocol, which in the most abstract terms has many
properties of a modified link-state protocol when distributing
information northbound and a distance vector protocol when
distributing information southbound. While this is an unusual
combination, it does quite naturally exhibit desired properties.
5. Overview
5.1. Properties
The most singular property of RIFT is that it floods link-state
information northbound only so that each level obtains the full
topology of levels south of it. Link-State information is, with some
exceptions, not flooded East-West or back South again. Exceptions
like south reflection is explained in detail in Section 6.5.1 and
east-west flooding at ToF level in multi-plane fabrics is outlined in
Section 5.2. In the southbound direction, the necessary routing
information required (normally just a default route as per
Section 6.3.8) only propagates one hop south. Those nodes then
generate their own routing information and flood it south to avoid
the overhead of building an update per adjacency. For the moment
describing the East-West direction is left out.
Those information flow constraints create not only an anisotropic
protocol (i.e. the information is not distributed "evenly" or
"clumped" but summarized along the N-S gradient) but also a "smooth"
information propagation where nodes do not receive the same
information from multiple directions at the same time. Normally,
accepting the same reachability on any link, without understanding
its topological significance, forces tie-breaking on some kind of
distance metric. And such tie-breaking leads ultimately to hop-by-
hop forwarding by shortest paths only. In contrast to that, RIFT,
under normal conditions, does not need to tie-break the same
reachability information from multiple directions. Its computation
principles (south forwarding direction is always preferred) leads to
valley-free [VFR] forwarding behavior. And since valley free routing
is loop-free, it can use all feasible paths. This is another highly
desirable property if available bandwidth should be utilized to the
maximum extent possible.
To account for the "northern" and the "southern" information split
the link state database is partitioned accordingly into "north
representation" and "south representation" Topology Information
Elements (TIEs). In simplest terms the North TIEs contain a link
state topology description of lower levels and South TIEs carry
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simply node description of the level above and default routes
pointing north. This oversimplified view will be refined gradually
in the following sections while introducing protocol procedures and
state machines at the same time.
5.2. Generalized Topology View
This section and resulting Section 6.5.2 are dedicated to multi-plane
fabrics, in contrast with the single plane designs where all ToF
nodes are topologically equal and initially connected to all the
switches at the level below them.
Multi-plane design is effectively a multi-dimensional switching
matrix. To make that easier to visualize, this document introduces a
methodology depicting the connectivity in two-dimensional pictures.
Further, it can be leveraged that what is under consideration here
are basically stacked crossbar fabrics where ports align "on top of
each other" in a regular fashion.
A word of caution to the reader; at this point it should be observed
that the language used to describe Clos variations, especially in
multi-plane designs, varies widely between sources. This description
follows the terminology introduced in Section 3.1. This terminology
is needed to follow the rest of this section correctly.
5.2.1. Terminology and Glossary
This section describes the terminology and acronyms used in the rest
of the text. Though the glossary may not be clear on a first read,
the following sections will introduce the terms in their proper
context.
P:
Denotes the number of PoDs in a topology.
S:
Denotes the number of ToF nodes in a topology.
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K:
To simplify the visual aids, notations and further considerations,
the assumption is made that the switches are symmetrical, i.e.,
they have an equal number of ports pointing northbound and
southbound. With that simplification, K denotes half of the radix
of a symmetrical switch, meaning that the switch has K ports
pointing north and K ports pointing south. K_LEAF (K of a leaf)
thus represents both the number of access ports in a leaf Node and
the maximum number of planes in the fabric, whereas K_TOP (K of a
ToP) represents the number of leaves in the PoD and the number of
ports pointing north in a ToP Node towards a higher spine level
and thus the number of ToF nodes in a plane.
ToF Plane:
Set of ToFs that are aware of each other by means of south
reflection. Planes are designated by capital letters, e.g. plane
A.
N:
Denotes the number of independent ToF planes in a topology.
R:
Denotes a redundancy factor, i.e., number of connections a spine
has towards a ToF plane. In single plane design K_TOP is equal to
R.
Fallen Leaf:
A fallen leaf in a plane Z is a switch that lost all connectivity
northbound to Z.
5.2.2. Clos as Crossed, Stacked Crossbars
The typical topology for which RIFT is defined is built of P number
of PoDs and connected together by S number of ToF nodes. A PoD node
has K number of ports. From here on half of them (K=Radix/2) are
assumed to connect host devices from the south, and the other half to
connect to interleaved PoD Top-Level switches to the north. The K
ratio can be chosen differently without loss of generality when port
speeds differ or the fabric is oversubscribed but K=Radix/2 allows
for more readable representation whereby there are as many ports
facing north as south on any intermediate node. A node is hence
represented in a schematic fashion with ports "sticking out" to its
north and south rather than by the usual real-world front faceplate
designs of the day.
Figure 4 provides a view of a leaf node as seen from the north, i.e.
showing ports that connect northbound. For lack of a better symbol,
the document chooses to use the "o" as ASCII visualisation of a
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single port. In this example, K_LEAF has 6 ports. Observe that the
number of PoDs is not related to Radix unless the ToF Nodes are
constrained to be the same as the PoD nodes in a particular
deployment.
Top view
+---+
| |
| O | e.g., Radix = 12, K_LEAF = 6
| |
| O |
| | -------------------------
| o <------ Physical Port (Ethernet) ----+
| | ------------------------- |
| O | |
| | |
| O | |
| | |
| O | |
| | |
+---+ v
|| || || || || || ||
+----+ +------------------------------------------------+
| | | |
+----+ +------------------------------------------------+
|| || || || || || ||
Side views
Figure 4: A Leaf Node, K_LEAF=6
The Radix of a PoD's top node may be different than that of the leaf
node. Though, more often than not, a same type of node is used for
both, effectively forming a square (K*K). In the general case,
switches at the top of the PoD with K_TOP southern ports not
necessarily equal to K_LEAF could be considered . For instance, in
the representations below, we pick a 6 port K_LEAF and an 8 port
K_TOP. In order to form a crossbar, K_TOP Leaf Nodes are necessary
as illustrated in Figure 5.
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+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
| | | | | | | | | | | | | | | |
| O | | O | | O | | O | | O | | O | | O | | O |
| | | | | | | | | | | | | | | |
| O | | O | | O | | O | | O | | O | | O | | O |
| | | | | | | | | | | | | | | |
| O | | O | | O | | O | | O | | O | | O | | O |
| | | | | | | | | | | | | | | |
| O | | O | | O | | O | | O | | O | | O | | O |
| | | | | | | | | | | | | | | |
| O | | O | | O | | O | | O | | O | | O | | O |
| | | | | | | | | | | | | | | |
| O | | O | | O | | O | | O | | O | | O | | O |
| | | | | | | | | | | | | | | |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
Figure 5: Southern View of Leaf Nodes of a PoD, K_TOP=8
As further visualized in Figure 6 the K_TOP Leaf Nodes are fully
interconnected with the K_LEAF ToP nodes, providing connectivity that
can be represented as a crossbar when "looked at" from the north.
The result is that, in the absence of a failure, a packet entering
the PoD from the north on any port can be routed to any port in the
south of the PoD and vice versa. And that is precisely why it makes
sense to talk about a "switching matrix".
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W <---*---> E
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
| | | | | | | | | | | | | | | |
+--------------------------------------------------------+
| o o o o o o o o |
+--------------------------------------------------------+
+--------------------------------------------------------+
| o o o o o o o o |
+--------------------------------------------------------+
+--------------------------------------------------------+
| o o o o o o o o |
+--------------------------------------------------------+
+--------------------------------------------------------+
| o o o o o o o o |
+--------------------------------------------------------+
+--------------------------------------------------------+
| o o o o o o o o |<--+
+--------------------------------------------------------+ |
+--------------------------------------------------------+ |
| o o o o o o o o | |
+--------------------------------------------------------+ |
| | | | | | | | | | | | | | | | |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ |
^ |
| |
| ---------- ----------------------- |
+----- Leaf Node Top-of-PoD Node (Spine) --+
---------- -----------------------
Figure 6: Northern View of a PoD's Spines, K_TOP=8
Side views of this PoD is illustrated in Figure 7 and Figure 8.
Connecting to Spine Nodes
|| || || || || || || ||
+----------------------------------------------------------------+ N
| Top-of-PoD Node (Sideways) | ^
+----------------------------------------------------------------+ |
|| || || || || || || || *
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+ |
|Leaf| |Leaf| |Leaf| |Leaf| |Leaf| |Leaf| |Leaf| |Leaf| v
|Node| |Node| |Node| |Node| |Node| |Node| |Node| |Node| S
+----+ +----+ +----+ +----+ +----+ +----+ +----+ +----+
|| || || || || || || ||
Connecting to Client Nodes
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Figure 7: Side View of a PoD, K_TOP=8, K_LEAF=6
Connecting to Spine Nodes
|| || || || || ||
+----+ +----+ +----+ +----+ +----+ +----+ N
|ToP | |ToP | |ToP | |ToP | |ToP | |ToP | ^
|Node| |Node| |Node| |Node| |Node| |Node| |
+----+ +----+ +----+ +----+ +----+ +----+ *
|| || || || || || |
+------------------------------------------------+ v
| Leaf Node (Sideways) | S
+------------------------------------------------+
Connecting to Client Nodes
Figure 8: Other Side View of a PoD, K_TOP=8, K_LEAF=6, 90 Degree
Turn in E-W Plane from the Previous Figure
As a next step, observe that a resulting PoD can be abstracted as a
bigger node with a number K of K_POD= K_TOP * K_LEAF, and the design
can recurse.
It will be critical at this point that, before progressing further,
the concept and the picture of "crossed crossbars" is understood.
Else, the following considerations might be difficult to comprehend.
To continue, the PoDs are interconnected with each other through a
ToF node at the very top or the north edge of the fabric. The
resulting ToF is *not* partitioned if, and only if (IIF), every PoD
top level node (spine) is connected to every ToF Node. This topology
is also referred to as a single plane configuration and is quite
popular due to its simplicity. In order to reach a 1:1 connectivity
ratio between the ToF and the leaves, it results that there are K_TOP
ToF nodes, because each port of a ToP node connects to a different
ToF node, and K_LEAF ToP nodes for the same reason. Consequently, it
will take at least (P * K_LEAF) ports on a ToF node to connect to
each of the K_LEAF ToP nodes of the P PoDs. Figure 9 illustrates
this, looking at P=3 PoDs from above and 2 sides. The large view is
the one from above, with the 8 ToF of 3*6 ports each interconnecting
the PoDs, every ToP Node being connected to every ToF node.
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[ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] <-----+
| | | | | | | | |
[=================================] | --------------
| | | | | | | | +----- Top-of-Fabric
[ ] [ ] [ ] [ ] [ ] [ ] [ ] [ ] +----- Node ---+
| -------------- |
| v
+-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ <-----+ +-+
| | | | | | | | | | | | | | | | | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] ------------------------- | |
[ |o| |o| |o| |o| |o| |o| |o| |o<--- Physical Port (Ethernet) | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] ------------------------- | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | |
| | | | | | | | | | | | | | | | | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] ---------- | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] <--- ToP Node --------+ | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] (Spine) | | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] ---------- | | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | | |
| | | | | | | | | | | | | | | | -+ +- +-+ v | |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | | --| |--[ ]--| |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | ----- | --| |--[ ]--| |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] +--- PoD ---+ --| |--[ ]--| |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | ----- | --| |--[ ]--| |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | | --| |--[ ]--| |
[ |o| |o| |o| |o| |o| |o| |o| |o| ] | | --| |--[ ]--| |
| | | | | | | | | | | | | | | | -+ +- +-+ | |
+-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+
Figure 9: Fabric Spines and TOFs in Single Plane Design, 3 PoDs
The top view can be collapsed into a third dimension where the hidden
depth index is representing the PoD number. One PoD can be shown
then as a class of PoDs and hence save one dimension in the
representation. The Spine Node expands in the depth and the vertical
dimensions, whereas the PoD top level Nodes are constrained, in
horizontal dimension. A port in the 2-D representation represents
effectively the class of all the ports at the same position in all
the PoDs that are projected in its position along the depth axis.
This is shown in Figure 10.
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/ / / / / / / / / / / / / / / /
/ / / / / / / / / / / / / / / /
/ / / / / / / / / / / / / / / /
/ / / / / / / / / / / / / / / / ]
+-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ ]]
| | | | | | | | | | | | | | | | ] ----------------
[ |o| |o| |o| |o| |o| |o| |o| |o| ] <-- ToP Node (Spine)
[ |o| |o| |o| |o| |o| |o| |o| |o| ] ----------------
[ |o| |o| |o| |o| |o| |o| |o| |o| ]]]]
[ |o| |o| |o| |o| |o| |o| |o| |o| ]]] ^^
[ |o| |o| |o| |o| |o| |o| |o| |o| ]] // PoDs
[ |o| |o| |o| |o| |o| |o| |o| |o| ] // (in depth)
| |/| |/| |/| |/| |/| |/| |/| |/ //
+-+ +-+ +-+/+-+/+-+ +-+ +-+ +-+ //
^
| ------------------
+----- Top-of-Fabric Node
------------------
Figure 10: Collapsed Northern View of a Fabric for Any Number of PoDs
As simple as a single plane deployment is, it introduces a limit due
to the bound on the available radix of the ToF nodes that has to be
at least P * K_LEAF. Nevertheless, it will become clear that a
distinct advantage of a connected or non-partitioned ToF is that all
failures can be resolved by simple, non-transitive, positive
disaggregation (i.e., nodes advertising more specific prefixes with
the default to the level below them that is, however, not propagated
further down the fabric) as described in Section 6.5.1 . In other
words, non-partitioned ToF nodes can always reach nodes below or
withdraw the routes from PoDs they cannot reach unambiguously. And
with this, positive disaggregation can heal all failures and still
allow all the ToF nodes to be aware of each other via south
reflection. Disaggregation will be explained in further detail in
Section 6.5.
In order to scale beyond the "single plane limit", the ToF can be
partitioned into N number of identically wired planes where N is an
integer divider of K_LEAF. The 1:1 ratio and the desired symmetry
are still served, this time with (K_TOP * N) ToF nodes, each of (P *
K_LEAF / N) ports. N=1 represents a non-partitioned Spine and
N=K_LEAF is a maximally partitioned Spine. Further, if R is any
integer divisor of K_LEAF, then N=K_LEAF/R is a feasible number of
planes and R a redundancy factor that denotes the number of
independent paths between 2 leaves within a plane. It proves
convenient for deployments to use a radix for the leaf nodes that is
a power of 2 so they can pick a number of planes that is a lower
power of 2. The example in Figure 11 splits the Spine in 2 planes
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with a redundancy factor R=3, meaning that there are 3 non-
intersecting paths between any leaf node and any ToF node. A ToF
node must have, in this case, at least 3*P ports, and be directly
connected to 3 of the 6 ToP nodes (spines) in each PoD. The ToP
nodes are represented horizontally with K_TOP=8 ports northwards
each.
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | O | | O | | O | | O | | O | | O | | O | | O | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | O | | O | | O | | O | | O | | O | | O | | O | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | O | | O | | O | | O | | O | | O | | O | | O | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
Plane 1
----------- . ------------ . ------------ . ------------ . --------
Plane 2
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | O | | O | | O | | O | | O | | O | | O | | O | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | O | | O | | O | | O | | O | | O | | O | | O | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+-| |--| |--| |--| |--| |--| |--| |--| |-+
| | O | | O | | O | | O | | O | | O | | O | | O | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
^
|
| ----------------
+----- Top-of-Fabric node
"across" depth
----------------
Figure 11: Northern View of a Multi-Plane ToF Level, K_LEAF=6, N=2
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At the extreme end of the spectrum it is even possible to fully
partition the spine with N = K_LEAF and R=1, while maintaining
connectivity between each leaf node and each ToF node. In that case
the ToF node connects to a single Port per PoD, so it appears as a
single port in the projected view represented in Figure 12. The
number of ports required on the Spine Node is more than or equal to
P, the number of PoDs.
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Plane 1
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ -+
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
| | O | | O | | O | | O | | O | | O | | O | | O | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ |
----------- . ------------------- . ------------ . ------- |
Plane 2 |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
| | O | | O | | O | | O | | O | | O | | O | | O | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ |
----------- . ------------ . ---- . ------------ . ------- |
Plane 3 |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
| | O | | O | | O | | O | | O | | O | | O | | O | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ |
----------- . ------------ . ------------------- . --------+<-+
Plane 4 | |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
| | O | | O | | O | | O | | O | | O | | O | | O | | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | |
----------- . ------------ . ------------ . ---- . ------- | |
Plane 5 | |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
| | O | | O | | O | | O | | O | | O | | O | | O | | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | |
----------- . ------------ . ------------ . -------------- | |
Plane 6 | |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
| | O | | O | | O | | O | | O | | O | | O | | O | | | |
+-| |--| |--| |--| |--| |--| |--| |--| |-+ | |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ -+ |
^ |
| |
| ---------------- ------------- |
+----- ToF Node Class of PoDs ---+
---------------- -------------
Figure 12: Northern View of a Maximally Partitioned ToF Level, R=1
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5.3. Fallen Leaf Problem
As mentioned earlier, RIFT exhibits an anisotropic behavior tailored
for fabrics with a North / South orientation and a high level of
interleaving paths. A non-partitioned fabric makes a total loss of
connectivity between a ToF node at the north and a leaf node at the
south a very rare but yet possible occasion that is fully healed by
positive disaggregation as described in Section 6.5.1. In large
fabrics or fabrics built from switches with low radix, the ToF may
often become partitioned in planes which makes the occurrence of
having a given leaf being only reachable from a subset of the ToF
nodes more likely to happen. This makes some further considerations
necessary.
A "Fallen Leaf" is a leaf that can be reached by only a subset of ToF
nodes due to missing connectivity. If R is the redundancy factor,
then it takes at least R breakages to reach a "Fallen Leaf"
situation.
In a maximally partitioned fabric, the redundancy factor is R=1, so
any breakage in the fabric will cause one or more fallen leaves in
the affected plane. R=2 guarantees that a single breakage will not
cause a fallen leaf. However, not all cases require disaggregation.
The following cases do not require particular action:
If a southern link on a node goes down, then connectivity through
that node is lost for all nodes south of it. There is no need to
disaggregate since the connectivity to this node is lost for all
spine nodes in a same fashion.
If a ToF Node goes down, then northern traffic towards it is
routed via alternate ToF nodes in the same plane and there is no
need to disaggregate routes.
In a general manner, the mechanism of non-transitive positive
disaggregation is sufficient when the disaggregating ToF nodes
collectively connect to all the ToP nodes in the broken plane. This
happens in the following case:
If the breakage is the last northern link from a ToP node to a ToF
node going down, then the fallen leaf problem affects only that
ToF node, and the connectivity to all the nodes in the PoD is lost
from that ToF node. This can be observed by other ToF nodes
within the plane where the ToP node is located and positively
disaggregated within that plane.
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On the other hand, there is a need to disaggregate the routes to
Fallen Leaves within the plane in a transitive fashion, that is, all
the way to the other leaves, in the following cases:
* If the breakage is the last northern link from a leaf node within
a plane (there is only one such link in a maximally partitioned
fabric) that goes down, then connectivity to all unicast prefixes
attached to the leaf node is lost within the plane where the link
is located. Southern Reflection by a leaf node, e.g., between ToP
nodes, if the PoD has only 2 levels, happens in between planes,
allowing the ToP nodes to detect the problem within the PoD where
it occurs and positively disaggregate. The breakage can be
observed by the ToF nodes in the same plane through the North
flooding of TIEs from the ToP nodes. The ToF nodes however need
to be aware of all the affected prefixes for the negative,
possibly transitive disaggregation to be fully effective (i.e., a
node advertising in the control plane that it cannot reach a
certain more specific prefix than default whereas such
disaggregation must in the extreme condition propagate further
down southbound). The problem can also be observed by the ToF
nodes in the other planes through the flooding of North TIEs from
the affected leaf nodes, together with non-node North TIEs which
indicate the affected prefixes. To be effective in that case, the
positive disaggregation must reach down to the nodes that make the
plane selection, which are typically the ingress leaf nodes. The
information is not useful for routing in the intermediate levels.
* If the breakage is a ToP node in a maximally partitioned fabric
(in which case it is the only ToP node serving the plane in that
PoD that goes down), then the connectivity to all the nodes in the
PoD is lost within the plane where the ToP node is located.
Consequently, all leaves of the PoD fall in this plane. Since the
Southern Reflection between the ToF nodes happens only within a
plane, ToF nodes in other planes cannot discover fallen leaves in
a different plane. They also cannot determine beyond their local
plane whether a leaf node that was initially reachable has become
unreachable. As the breakage can be observed by the ToF nodes in
the plane where the breakage happened, the ToF nodes in the plane
need to be aware of all the affected prefixes for the negative
disaggregation to be fully effective. The problem can also be
observed by the ToF nodes in the other planes through the flooding
of North TIEs from the affected leaf nodes, if there are only 3
levels and the ToP nodes are directly connected to the leaf nodes,
and then again it can only be effective if it is propagated
transitively to the leaf, and useless above that level.
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These abstractions are rolled back into a simplified example that
shows that in Figure 3 the loss of link between spine node 3 and leaf
node 3 will make leaf node 3 a fallen leaf for ToF nodes in plane C.
Worse, if the cabling was never present in the first place, plane C
will not even be able to know that such a fallen leaf exists. Hence
partitioning without further treatment results in two grave problems:
* Leaf node 1 trying to route to leaf node 3 must not choose spine
node 3 in plane C as its next hop since it will inevitably drop
the packet when forwarding using default routes or do excessive
bow-tying. This information must be in its routing table.
* A path computation trying to deal with the problem by distributing
host routes may only form paths through leaves. The flooding of
information about leaf node 3 would have to go up to ToF nodes in
planes A, B, and D and then "loopback" over other leaves to ToF C
leading in extreme cases to traffic for leaf node 3 when presented
to plane C taking an "inverted fabric" path where leaves start to
serve as ToFs, at least for the duration of a protocol's
convergence.
5.4. Discovering Fallen Leaves
When aggregation is used, RIFT deals with fallen leaves by ensuring
that all the ToF nodes share the same north topology database. This
happens naturally in single plane design by the means of northbound
flooding and south reflection but needs additional considerations in
multi-plane fabrics. To enable routing to fallen leaves in multi-
plane designs, RIFT requires additional interconnection across planes
between the ToF nodes, e.g., using rings as illustrated in Figure 13.
Other solutions are possible but they either need more cabling or end
up having much longer flooding paths and/or single points of failure.
In detail, by reserving at least two ports on each ToF node it is
possible to connect them together by interplane bi-directional rings
as illustrated in Figure 13. The rings will be used to exchange full
north topology information between planes. All ToFs having the same
north topology allows by the means of transitive, negative
disaggregation described in Section 6.5.2 to efficiently fix any
possible fallen leaf scenario. Somewhat as a side-effect, the
exchange of information fulfills the requirement for a full view of
the fabric topology at the ToF level, without the need to collate it
from multiple points.
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____________________________________________________________________________
| [Plane A] . [Plane B] . [Plane C] . [Plane D] |
|..........................................................................|
| +-------------------------------------------------------------+ |
| | +---+ . +---+ . +---+ . +---+ | |
| +-+ n +-------------+ n +-------------+ n +-------------+ n +-+ |
| +--++ . +-+++ . +-+++ . +--++ |
| || . || . || . || |
| +---------||---------------||----------------||---------------+ || |
| | +---+ || . +---+ || . +---+ || . +---+ | || |
| +-+ 1 +---||--------+ 1 +--||---------+ 1 +--||---------+ 1 +-+ || |
| +--++ || . +-+++ || . +-+++ || . +-+++ || |
| || || . || || . || || . || || |
| || || . || || . || || . || || |
Figure 13: Using rings to bring all planes and at the ToF bind them
5.5. Addressing the Fallen Leaves Problem
One consequence of the "Fallen Leaf" problem is that some prefixes
attached to the fallen leaf become unreachable from some of the ToF
nodes. RIFT defines two methods to address this issue denoted as
positive disaggregation and negative disaggregation. Both methods
flood corresponding types of South TIEs to advertise the impacted
prefix(es).
When used for the operation of disaggregation, a positive South TIE,
as usual, indicates reachability to a prefix of given length and all
addresses subsumed by it. In contrast, a negative route
advertisement indicates that the origin cannot route to the
advertised prefix.
The positive disaggregation is originated by a router that can still
reach the advertised prefix, and the operation is not transitive. In
other words, the receiver does *not* generate its own TIEs or flood
them south as a consequence of receiving positive disaggregation
advertisements from a higher level node. The effect of a positive
disaggregation is that the traffic to the impacted prefix will follow
the longest match and will be limited to the northbound routers that
advertised the more specific route.
In contrast, the negative disaggregation can be transitive, and is
propagated south when all the possible routes have been advertised as
negative exceptions. A negative route advertisement is only
actionable when the negative prefix is aggregated by a positive route
advertisement for a shorter prefix. In such case, the negative
advertisement "punches out a hole" in the positive route in the
routing table, making the positive prefix reachable through the
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originator with the special consideration of the negative prefix
removing certain next hop neighbors. The specific procedures will be
explained in detail in Section 6.5.2.3.
When the ToF switches are not partitioned into multiple planes, the
resulting southbound flooding of the positive disaggregation by the
ToF nodes that can still reach the impacted prefix is in general
enough to cover all the switches at the next level south, typically
the ToP nodes. If all those switches are aware of the
disaggregation, they collectively create a ceiling that intercepts
all the traffic north and forwards it to the ToF nodes that
advertised the more specific route. In that case, the positive
disaggregation alone is sufficient to solve the fallen leaf problem.
On the other hand, when the fabric is partitioned in planes, the
positive disaggregation from ToF nodes in different planes do not
reach the ToP switches in the affected plane and cannot solve the
fallen leaves problem. In other words, a breakage in a plane can
only be solved in that plane. Also, the selection of the plane for a
packet typically occurs at the leaf level and the disaggregation must
be transitive and reach all the leaves. In that case, the negative
disaggregation is necessary. The details on the RIFT approach to
deal with fallen leaves in an optimal way are specified in
Section 6.5.2.
6. Specification
This section specifies the protocol in a normative fashion by either
prescriptive procedures or behavior defined by Finite State Machines
(FSM).
The FSMs, as usual, are presented as states a neighbor can assume,
events that can occur, and the corresponding actions performed when
transitioning between states on event processing.
Actions are performed before the end state is assumed.
The FSMs can queue events against itself to chain actions or against
other FSMs in the specification. Events are always processed in the
sequence they have been queued.
Consequently, "On Entry" actions for an FSM state are performed every
time and right before the corresponding state is entered, i.e., after
any transitions from previous state.
"On Exit" actions are performed every time and immediately when a
state is exited, i.e., before any transitions towards target state
are performed.
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Any attempt to transition from a state towards another on reception
of an event where no action is specified MUST be considered an
unrecoverable error and the protocol MUST reset all adjacencies and
discard all the state (i.e., force the FSM back to _OneWay_ and flush
all of the queues holding flooding information).
The data structures and FSMs described in this document are
conceptual and do not have to be implemented precisely as described
here, i.e., an implementation is considered conforming as long as it
supports the described functionality and exhibits externally
observable behavior equivalent to the behavior of the standardized
FSMs.
The FSMs can use "timers" for different situations. Those timers are
started through actions and their expiration leads to queuing of
corresponding events to be processed.
The term "holdtime" is used often as short-hand for "holddown timer"
and signifies either the length of the holding down period or the
timer used to expire after such period. Such timers are used to
"hold down" state within an FSM that is cleaned if the machine
triggers a _HoldtimeExpired_ event.
6.1. Transport
All normative RIFT packet structures and their contents are defined
in the Thrift [thrift] models in Appendix B. The packet structure
itself is defined in _ProtocolPacket_ which contains the packet
header in _PacketHeader_ and the packet contents in _PacketContent_.
_PacketContent_ is a union of the LIE, TIE, TIDE, and TIRE packets
which are subsequently defined in _LIEPacket_, _TIEPacket_,
_TIDEPacket_, and _TIREPacket_ respectively.
Further, in terms of bits on the wire, it is the _ProtocolPacket_
that is serialized and carried in an envelope defined in
Section 6.9.3 within a UDP frame that provides security and allows
validation/modification of several important fields without Thrift
de-serialization for performance and security reasons. Security
model and procedures are further explained in Section 9.
6.2. Link (Neighbor) Discovery (LIE Exchange)
RIFT LIE exchange auto-discovers neighbors, negotiates ZTP parameters
and discovers miscablings. The formation progresses under normal
conditions from _OneWay_ to _TwoWay_ and then _ThreeWay_ state at
which point it is ready to exchange TIEs per Section 6.3. The
adjacency exchanges ZTP information (Section 6.7) in any of the
states, i.e. it is not necessary to reach _ThreeWay_ for zero-touch
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provisioning to operate.
RIFT supports any combination of IPv4 and IPv6 addressing on the
fabric with the additional capability for forwarding paths that are
capable of forwarding IPv4 packets in presence of IPv6 addressing
only.
IPv4 LIE exchange happens over well-known administratively locally
scoped and configured or otherwise well-known IPv4 multicast address
[RFC2365]. For IPv6 [RFC8200] exchange is performed over link-local
multicast scope [RFC4291] address which is configured or otherwise
well-known. In both cases a destination UDP port defined in the
schema Appendix B.2 is used unless configured otherwise. LIEs MUST
be sent with an IPv4 Time to Live (TTL) or an IPv6 Hop Limit (HL) of
either 1 or 255 to prevent RIFT information reaching beyond a single
L3 next-hop in the topology. LIEs SHOULD be sent with network
control precedence unless an implementation is prevented from doing
so [RFC2474].
The originating port of the LIE has no further significance other
than identifying the origination point. LIEs are exchanged over all
links running RIFT.
An implementation may listen and send LIEs on IPv4 and/or IPv6
multicast addresses. A node MUST NOT originate LIEs on an address
family if it does not process received LIEs on that family. LIEs on
the same link are considered part of the same LIE FSM independent of
the address family they arrive on. The LIE source address may not
identify the peer uniquely in unnumbered or link-local address cases
so the response transmission MUST occur over the same interface the
LIEs have been received on. A node may use any of the adjacency's
source addresses it saw in LIEs on the specific interface during
adjacency formation to send TIEs (Section 6.3.3). That implies that
an implementation MUST be ready to accept TIEs on all addresses it
used as source of LIE frames.
A simplified version MAY be implemented on platforms with limited or
no multicast support (e.g. IoT devices) by sending and receiving LIE
frames on IPv4 subnet broadcast addresses or IPv6 all routers
multicast address. However, this technique is less optimal and
presents a wider attack surface from a security perspective.
A _ThreeWay_ adjacency (as defined in the glossary) over any address
family implies support for IPv4 forwarding if the
_ipv4_forwarding_capable_ flag in _LinkCapabilities_ is set to true.
In the absence of IPv4 LIEs with _ipv4_forwarding_capable_ set to
true, a node MUST forward IPv4 packets using gateways discovered on
IPv6-only links advertising this capability. The mechanism to
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discover the corresponding IPv6 gateway is out of scope for this
specification and may be implementation specific. It is expected
that the whole fabric supports the same type of forwarding of address
families on all the links, any other combination is outside the scope
of this specification. If IPv4 forwarding is supported on an
interface, _ipv4_forwarding_capable_ MUST be set to true for all LIEs
advertised from that interface. If IPv4 and IPv6 LIEs indicate
contradicting information, protocol behavior is unspecified.
Operation of a fabric where only some of the links are supporting
forwarding on an address family or have an address in a family and
others do not is outside the scope of this specification.
Any attempt to construct IPv6 forwarding over IPv4 only adjacencies
is outside this specification.
Table 1 outlines protocol behavior pertaining to LIE exchange over
different address family combinations. Table 2 outlines the way in
which neighbors forward traffic as it pertains to the
_ipv4_forwarding_capable_ flag setting across the same address family
combinations.
The specific forwarding implementation to support the described
behavior is out of scope for this document.
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+==========+==========+==========================================+
| Local | Remote | LIE Exchange Behavior |
| Neighbor | Neighbor | |
| AF | AF | |
+==========+==========+==========================================+
| IPv4 | IPv4 | LIEs and TIEs are exchanged over IPv4 |
| | | only. The local neighbor receives TIEs |
| | | from remote neighbors on any of the LIE |
| | | source addresses. |
+----------+----------+------------------------------------------+
| IPv6 | IPv6 | LIEs and TIEs are exchanged over IPv6 |
| | | only. The local neighbor receives TIEs |
| | | from remote neighbors on any of the LIE |
| | | source addresses. |
+----------+----------+------------------------------------------+
| IPv4, | IPv6 | The local neighbor sends LIEs for both |
| IPv6 | | IPv4 and IPv6 while the remote neighbor |
| | | only sends LIEs for IPv6. The resulting |
| | | adjacency will exchange TIEs over IPv6 |
| | | on any of the IPv6 LIE source addresses. |
+----------+----------+------------------------------------------+
| IPv4, | IPv4, | LIEs and TIEs are exchanged over IPv6 |
| IPv6 | IPv6 | and IPv4. TIEs are received on any of |
| | | the IPv4 or IPv6 LIE source addresses. |
| | | The local neighbor receives TIEs from |
| | | the remote neighbors on any of the IPv4 |
| | | or IPv6 LIE source addresses. |
+----------+----------+------------------------------------------+
Table 1: Control Plane Behavior for Neighbor AF Combinations
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+==========+==========+==========================================+
| Local | Remote | Forwarding Behavior |
| Neighbor | Neighbor | |
| AF | AF | |
+==========+==========+==========================================+
| IPv4 | IPv4 | Both nodes are required to set the |
| | | _ipv4_forwarding_capable_ flag to true. |
| | | Only IPv4 traffic can be forwarded. |
+----------+----------+------------------------------------------+
| IPv6 | IPv6 | If either neighbor sets |
| | | _ipv4_forwarding_capable_ to false, only |
| | | IPv6 traffic can be forwarded. If both |
| | | neighbors set _ipv4_forwarding_capable_ |
| | | to true, IPv4 traffic is also forwarded |
| | | via IPv6 gateways. |
+----------+----------+------------------------------------------+
| IPv4, | IPv6 | If the remote neighbor sets |
| IPv6 | | _ipv4_forwarding_capable_ to false, only |
| | | IPv6 traffic can be forwarded. If both |
| | | neighbors set _ipv4_forwarding_capable_ |
| | | to true, IPv4 traffic is also forwarded |
| | | via IPv6 gateways. |
+----------+----------+------------------------------------------+
| IPv4, | IPv4, | IPv4 and IPv6 traffic can be forwarded. |
| IPv6 | IPv6 | If IPv4 and IPv6 LIEs advertise |
| | | conflicting _ipv4_forwarding_capable_ |
| | | flags, the behavior is unspecified. |
+----------+----------+------------------------------------------+
Table 2: Forwarding Behavior for Neighbor AF Combinations
The protocol does *not* support selective disabling of address
families after adjacency formation, disabling IPv4 forwarding
capability or any local address changes in _ThreeWay_ state, i.e. if
a link has entered ThreeWay IPv4 and/or IPv6 with a neighbor on an
adjacency and it wants to stop supporting one of the families or
change any of its local addresses or stop IPv4 forwarding, it MUST
tear down and rebuild the adjacency. It MUST also remove any state
it stored about the remote side of the adjacency such as associated
LIE source addresses.
Unless ZTP as described in Section 6.7 is used, each node is
provisioned with the level at which it is operating and advertises it
in the _level_ of the _PacketHeader_ schema element. It MAY be also
provisioned with its PoD. If level is not provisioned, it is not
present in the optional _PacketHeader_ schema element and established
by ZTP procedures if feasible. If PoD is not provisioned, it is
governed by the _LIEPacket_ schema element assuming the
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_common.default_pod_ value. This means that switches except ToF do
not need to be configured at all. Necessary information to configure
all values is exchanged in the _LIEPacket_ and _PacketHeader_ or
derived by the node automatically.
Further definitions of leaf flags are found in Section 6.7 given they
have implications in terms of level and adjacency forming here. Leaf
flags are carried in _HierarchyIndications_.
A node MUST form a _ThreeWay_ adjacency if at a minimum the following
first order logic conditions are satisfied on a LIE packet as
specified by the _LIEPacket_ schema element and received on a link
(such a LIE is considered a "minimally valid" LIE). Observe that
depending on the FSM involved and its state further conditions may be
checked and even a minimally valid LIE can be considered ultimately
invalid if any of the additional conditions fail.
1. the neighboring node is running the same major schema version as
indicated in the _major_version_ element in _PacketHeader_ *and*
2. the neighboring node uses a valid System ID (i.e. value different
from _IllegalSystemID_) in the _sender_ element in _PacketHeader_
*and*
3. the neighboring node uses a different System ID than the node
itself *and*
4. (the advertised MTU values in the _LiePacket_ element match on
both sides while a missing MTU in the _LiePacket_ element is
interpreted as _default_mtu_size_) *and*
5. both nodes advertise defined level values in _level_ element in
_PacketHeader_ *and*
6. [
i) the node is at _leaf_level_ value and has no _ThreeWay_
adjacencies already to nodes at Highest Adjacency _ThreeWay_
(HAT as defined later in Section 6.7.1) with level different
than the adjacent node *or*
ii) the node is not at _leaf_level_ value and the neighboring
node is at _leaf_level_ value *or*
iii) both nodes are at _leaf_level_ values *and* both indicate
support for Section 6.8.9 *or*
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iv) neither node is at _leaf_level_ value and the neighboring
node is at most one level difference away
].
LIEs arriving with IPv4 Time to Live (TTL) or an IPv6 Hop Limit (HL)
different than 1 or 255 MUST be ignored.
6.2.1. LIE Finite State Machine
This section specifies the precise, normative LIE FSM which is given
as well in Figure 14. Additionally, some sets of actions repeat
often and are hence summarized into well-known procedures.
Events generated are fairly fine grained, especially when indicating
problems in adjacency forming conditions to simplify tracking of
problems in deployment.
Initial state is _OneWay_.
The machine sends LIEs proactively on several transitions to
accelerate adjacency bring-up without waiting for the corresponding
timer tic.
Enter
|
V
+-----------+
| OneWay |<----+
| | | TimerTick
| | | LevelChanged
| | | HALChanged
| | | HATChanged
| | | HALSChanged
| | | LieRcvd
| | | NeighborDroppedReflection
| | | NeighborChangedLevel
| | | NeighborChangedAddress
| | | UnacceptableHeader
| | | MTUMismatch
| | | NeighborChangedMinorFields
| | | HoldtimeExpired
| | | FloodLeadersChanged
| | | SendLie
| | | UpdateZTPOffer
| |-----+
| |
| |<--------------------- (ThreeWay)
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| |--------------------->
| | ValidReflection
| |
| |---------------------> (Multiple
| | MultipleNeighbors Neighbors
+-----------+ Wait)
^ |
| |
| | NewNeighbor
| V
(TwoWay)
(OneWay)
| ^
| | NeighborChangedLevel
| | NeighborChangedAddress
| | UnacceptableHeader
| | MTUMismatch
| | HoldtimeExpired
| |
V |
+-----------+
| TwoWay |<----+
| | | TimerTick
| | | LevelChanged
| | | HALChanged
| | | HATChanged
| | | HALSChanged
| | | LieRcvd
| | | FloodLeadersChanged
| | | SendLie
| | | UpdateZTPOffer
| |-----+
| |
| |<----------------------
| |----------------------> (Multiple
| | NewNeighbor Neighbors
| | Wait)
| | MultipleNeighbors
+-----------+
^ |
| | ValidReflection
| V
(ThreeWay)
(TwoWay) (OneWay)
^ | ^
| | | LevelChanged
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| | | NeighborChangedLevel
| | | NeighborChangedAddress
| | | UnacceptableHeader
| | | MTUMismatch
| | | HoldtimeExpired
NeighborDropped- | | |
Reflection | | |
| V |
+-----------+ |
| ThreeWay |-----+
| |
| |<----+
| | | TimerTick
| | | HALChanged
| | | HATChanged
| | | HALSChanged
| | | LieRcvd
| | | ValidReflection
| | | FloodLeadersChanged
| | | SendLie
| | | UpdateZTPOffer
| |-----+
| |----------------------> (Multiple
| | MultipleNeighbors Neighbors
+-----------+ Wait)
(TwoWay) (ThreeWay)
| |
V V
+------------+
| Multiple |<----+
| Neighbors | | TimerTick
| Wait | | HALChanged
| | | HATChanged
| | | HALSChanged
| | | LieRcvd
| | | ValidReflection
| | | NeighborDroppedReflection
| | | NeighborChangedBFDCapability
| | | NeighborChangedAddress
| | | UnacceptableHeader
| | | MTUMismatch
| | | HoldtimeExpired
| | | MultipleNeighbors
| | | FloodLeadersChanged
| | | SendLie
| | | UpdateZTPOffer
| |-----+
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| |
| |<---------------------------
| |---------------------------> (OneWay)
| | LevelChanged
+------------+ MultipleNeighborsDone
Figure 14: LIE FSM
The following words are used for well-known procedures:
* PUSH Event: queues an event to be executed by the FSM upon exit of
this action
* CLEANUP: The FSM *conceptually* holds a `current neighbor`
variable that contains information received in the remote node's
LIE that is processed against LIE validation rules. In the event
that the LIE is considered to be invalid, the existing state held
by `current neighbor` MUST be deleted.
* SEND_LIE: create and send a new LIE packet
1. reflecting the _neighbor_ element as described in
ValidReflection and
2. setting the necessary _not_a_ztp_offer_ variable if level was
derived from the last known neighbor on this interface and
3. setting _you_are_flood_repeater_ variable to the computed
value
* PROCESS_LIE:
1. if LIE has a major version not equal to this node's major
version *or* System ID equal to (this node's System ID or
_IllegalSystemID_) then CLEANUP else
2. if both sides advertise MTU values and the MTU in the received
LIE does not match the MTU advertised by the local system *or*
at least one of the nodes does not advertise an MTU value and
the advertising node's LIE does not match the
_default_mtu_size_ of the system not advertising an MTU then
CLEANUP, PUSH UpdateZTPOffer, PUSH MTUMismatch else
3. if the LIE has an undefined level *or* this node's level is
undefined *or* this node is a leaf and remote level is lower
than HAT *or* (the LIE's level is not leaf *and* its
difference is more than one from this node's level) then
CLEANUP, PUSH UpdateZTPOffer, PUSH UnacceptableHeader else
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4. PUSH UpdateZTPOffer, construct temporary new neighbor
structure with values from LIE, if no current neighbor exists
then set current neighbor to new neighbor, PUSH NewNeighbor
event, CHECK_THREE_WAY else
1. if current neighbor System ID differs from LIE's System ID
then PUSH MultipleNeighbors else
2. if current neighbor stored level differs from LIE's level
then PUSH NeighborChangedLevel else
3. if current neighbor stored IPv4/v6 address differs from
LIE's address then PUSH NeighborChangedAddress else
4. if any of neighbor's flood address port, name, or local
LinkID changed then PUSH NeighborChangedMinorFields
5. CHECK_THREE_WAY
* CHECK_THREE_WAY: if current state is _OneWay_ do nothing else
1. if LIE packet does not contain neighbor then if current state
is _ThreeWay_ then PUSH NeighborDroppedReflection else
2. if packet reflects this system's ID and local port and state
is _ThreeWay_ then PUSH event ValidReflection else PUSH event
MultipleNeighbors
States:
* OneWay: initial state the FSM is starting from. In this state the
router did not receive any valid LIEs from a neighbor.
* TwoWay: that state is entered when a node has received a minimally
valid LIE from a neighbor but not a ThreeWay valid LIE.
* ThreeWay: this state signifies that _ThreeWay_ valid LIEs from a
neighbor have been received. On achieving this state the link can
be advertised in _neighbors_ element in _NodeTIEElement_.
* MultipleNeighborsWait: occurs normally when more than two nodes
become aware of each other on the same link or a remote node is
quickly reconfigured or rebooted without regressing to _OneWay_
first. Each occurrence of the event SHOULD generate notification
to help operational deployments.
Events:
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* TimerTick: one second timer tick, i.e., the event is provided to
the FSM once a second by an implementation-specific mechanism that
is outside the scope of this specification. This event is quietly
ignored if the relevant transition does not exist.
* LevelChanged: node's level has been changed by ZTP or
configuration. This is provided by the ZTP FSM.
* HALChanged: best HAL computed by ZTP has changed. This is
provided by the ZTP FSM.
* HATChanged: HAT computed by ZTP has changed. This is provided by
the ZTP FSM.
* HALSChanged: set of HAL offering systems computed by ZTP has
changed. This is provided by the ZTP FSM.
* LieRcvd: received LIE on the interface.
* NewNeighbor: new neighbor is present in the received LIE.
* ValidReflection: received valid reflection of this node from
neighbor, i.e. all elements in _neighbor_ element in _LiePacket_
have values corresponding to this link.
* NeighborDroppedReflection: lost previously held reflection from
neighbor, i.e. _neighbor_ element in _LiePacket_ does not
correspond to this node or is not present.
* NeighborChangedLevel: neighbor changed advertised level from the
previously held one.
* NeighborChangedAddress: neighbor changed IP address, i.e. LIE has
been received from an address different from previous LIEs. Those
changes will influence the sockets used to listen to TIEs, TIREs,
TIDEs.
* UnacceptableHeader: Unacceptable header received.
* MTUMismatch: MTU mismatched.
* NeighborChangedMinorFields: minor fields changed in neighbor's
LIE.
* HoldtimeExpired: adjacency holddown timer expired.
* MultipleNeighbors: more than one neighbor is present on interface
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* MultipleNeighborsDone: multiple neighbors timer expired.
* FloodLeadersChanged: node's election algorithm determined new set
of flood leaders.
* SendLie: send a LIE out.
* UpdateZTPOffer: update this node's ZTP offer. This is sent to the
ZTP FSM.
Actions:
* on HATChanged in _OneWay_ finishes in OneWay: store HAT
* on FloodLeadersChanged in _OneWay_ finishes in OneWay: update
_you_are_flood_repeater_ LIE elements based on flood leader
election results
* on UnacceptableHeader in _OneWay_ finishes in OneWay: no action
* on NeighborChangedMinorFields in _OneWay_ finishes in OneWay: no
action
* on SendLie in _OneWay_ finishes in OneWay: SEND_LIE
* on HALSChanged in _OneWay_ finishes in OneWay: store HALS
* on MultipleNeighbors in _OneWay_ finishes in
MultipleNeighborsWait: start multiple neighbors timer with
interval _multiple_neighbors_lie_holdtime_multipler_ *
_default_lie_holdtime_
* on NeighborChangedLevel in _OneWay_ finishes in OneWay: no action
* on LieRcvd in _OneWay_ finishes in OneWay: PROCESS_LIE
* on MTUMismatch in _OneWay_ finishes in OneWay: no action
* on ValidReflection in _OneWay_ finishes in ThreeWay: no action
* on LevelChanged in _OneWay_ finishes in OneWay: update level with
event value, PUSH SendLie event
* on HALChanged in _OneWay_ finishes in OneWay: store new HAL
* on HoldtimeExpired in _OneWay_ finishes in OneWay: no action
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* on NeighborChangedAddress in _OneWay_ finishes in OneWay: no
action
* on NewNeighbor in _OneWay_ finishes in TwoWay: PUSH SendLie event
* on UpdateZTPOffer in _OneWay_ finishes in OneWay: send offer to
ZTP FSM
* on NeighborDroppedReflection in _OneWay_ finishes in OneWay: no
action
* on TimerTick in _OneWay_ finishes in OneWay: PUSH SendLie event
* on FloodLeadersChanged in _TwoWay_ finishes in TwoWay: update
_you_are_flood_repeater_ LIE elements based on flood leader
election results
* on UpdateZTPOffer in _TwoWay_ finishes in TwoWay: send offer to
ZTP FSM
* on NewNeighbor in _TwoWay_ finishes in MultipleNeighborsWait: PUSH
SendLie event
* on ValidReflection in _TwoWay_ finishes in ThreeWay: no action
* on LieRcvd in _TwoWay_ finishes in TwoWay: PROCESS_LIE
* on UnacceptableHeader in _TwoWay_ finishes in OneWay: no action
* on HALChanged in _TwoWay_ finishes in TwoWay: store new HAL
* on HoldtimeExpired in _TwoWay_ finishes in OneWay: no action
* on LevelChanged in _TwoWay_ finishes in TwoWay: update level with
event value
* on TimerTick in _TwoWay_ finishes in TwoWay: PUSH SendLie event,
if last valid LIE was received more than _holdtime_ ago as
advertised by neighbor then PUSH HoldtimeExpired event
* on HATChanged in _TwoWay_ finishes in TwoWay: store HAT
* on NeighborChangedLevel in _TwoWay_ finishes in OneWay: no action
* on HALSChanged in _TwoWay_ finishes in TwoWay: store HALS
* on MTUMismatch in _TwoWay_ finishes in OneWay: no action
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* on NeighborChangedAddress in _TwoWay_ finishes in OneWay: no
action
* on SendLie in _TwoWay_ finishes in TwoWay: SEND_LIE
* on MultipleNeighbors in _TwoWay_ finishes in
MultipleNeighborsWait: start multiple neighbors timer with
interval _multiple_neighbors_lie_holdtime_multipler_ *
_default_lie_holdtime_
* on TimerTick in _ThreeWay_ finishes in ThreeWay: PUSH SendLie
event, if last valid LIE was received more than _holdtime_ ago as
advertised by neighbor then PUSH HoldtimeExpired event
* on LevelChanged in _ThreeWay_ finishes in OneWay: update level
with event value
* on HATChanged in _ThreeWay_ finishes in ThreeWay: store HAT
* on MTUMismatch in _ThreeWay_ finishes in OneWay: no action
* on UnacceptableHeader in _ThreeWay_ finishes in OneWay: no action
* on MultipleNeighbors in _ThreeWay_ finishes in
MultipleNeighborsWait: start multiple neighbors timer with
interval _multiple_neighbors_lie_holdtime_multipler_ *
_default_lie_holdtime_
* on NeighborChangedLevel in _ThreeWay_ finishes in OneWay: no
action
* on HALSChanged in _ThreeWay_ finishes in ThreeWay: store HALS
* on LieRcvd in _ThreeWay_ finishes in ThreeWay: PROCESS_LIE
* on FloodLeadersChanged in _ThreeWay_ finishes in ThreeWay: update
_you_are_flood_repeater_ LIE elements based on flood leader
election results, PUSH SendLie
* on NeighborDroppedReflection in _ThreeWay_ finishes in TwoWay: no
action
* on HoldtimeExpired in _ThreeWay_ finishes in OneWay: no action
* on ValidReflection in _ThreeWay_ finishes in ThreeWay: no action
* on UpdateZTPOffer in _ThreeWay_ finishes in ThreeWay: send offer
to ZTP FSM
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* on NeighborChangedAddress in _ThreeWay_ finishes in OneWay: no
action
* on HALChanged in _ThreeWay_ finishes in ThreeWay: store new HAL
* on SendLie in _ThreeWay_ finishes in ThreeWay: SEND_LIE
* on MultipleNeighbors in MultipleNeighborsWait finishes in
MultipleNeighborsWait: start multiple neighbors timer with
interval _multiple_neighbors_lie_holdtime_multipler_ *
_default_lie_holdtime_
* on FloodLeadersChanged in MultipleNeighborsWait finishes in
MultipleNeighborsWait: update _you_are_flood_repeater_ LIE
elements based on flood leader election results
* on TimerTick in MultipleNeighborsWait finishes in
MultipleNeighborsWait: check MultipleNeighbors timer, if timer
expired PUSH MultipleNeighborsDone
* on ValidReflection in MultipleNeighborsWait finishes in
MultipleNeighborsWait: no action
* on UpdateZTPOffer in MultipleNeighborsWait finishes in
MultipleNeighborsWait: send offer to ZTP FSM
* on NeighborDroppedReflection in MultipleNeighborsWait finishes in
MultipleNeighborsWait: no action
* on LieRcvd in MultipleNeighborsWait finishes in
MultipleNeighborsWait: no action
* on UnacceptableHeader in MultipleNeighborsWait finishes in
MultipleNeighborsWait: no action
* on NeighborChangedAddress in MultipleNeighborsWait finishes in
MultipleNeighborsWait: no action
* on LevelChanged in MultipleNeighborsWait finishes in OneWay:
update level with event value
* on HATChanged in MultipleNeighborsWait finishes in
MultipleNeighborsWait: store HAT
* on MTUMismatch in MultipleNeighborsWait finishes in
MultipleNeighborsWait: no action
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* on HALSChanged in MultipleNeighborsWait finishes in
MultipleNeighborsWait: store HALS
* on HALChanged in MultipleNeighborsWait finishes in
MultipleNeighborsWait: store new HAL
* on HoldtimeExpired in MultipleNeighborsWait finishes in
MultipleNeighborsWait: no action
* on SendLie in MultipleNeighborsWait finishes in
MultipleNeighborsWait: no action
* on MultipleNeighborsDone in MultipleNeighborsWait finishes in
OneWay: no action
* on Entry into OneWay: CLEANUP
6.3. Topology Exchange (TIE Exchange)
6.3.1. Topology Information Elements
Topology and reachability information in RIFT is conveyed by TIEs.
The TIE exchange mechanism uses the port indicated by each node in
the LIE exchange as _flood_port_ in _LIEPacket_ and the interface on
which the adjacency has been formed as destination. TIEs MUST be
sent with an IPv4 Time to Live (TTL) or an IPv6 Hop Limit (HL) of
either 1 or 255 and also MUST be ignored if received with values
different than 1 or 255. This prevents RIFT information from
reaching beyond a single L3 next-hop in the topology. TIEs SHOULD be
sent with network control precedence unless an implementation is
prevented from doing so [RFC2474].
TIEs contain sequence numbers, lifetimes, and a type. Each type has
ample identifying number space and information is spread across
multiple TIEs with the same TIEElement type (this is true for all TIE
types).
More information about the TIE structure can be found in the schema
in Appendix B starting with _TIEPacket_ root.
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6.3.2. Southbound and Northbound TIE Representation
A central concept of RIFT is that each node represents itself
differently depending on the direction in which it is advertising
information. More precisely, a spine node represents two different
databases over its adjacencies depending on whether it advertises
TIEs to the north or to the south/east-west. Those differing TIE
databases are called either south- or northbound (South TIEs and
North TIEs) depending on the direction of distribution.
The North TIEs hold all of the node's adjacencies and local prefixes
while the South TIEs hold only all of the node's adjacencies, the
default prefix with necessary disaggregated prefixes and local
prefixes. Section 6.5 explains further details.
All TIE types are mostly symmetrical in both directions. The
(Appendix B.3) defines the TIE types (i.e., the TIETypeType element)
and their directionality (i.e., _direction_ within the _TIEID_
element).
As an example illustrating a databases holding both representations,
the topology in Figure 2 with the optional link between spine 111 and
spine 112 (so that the flooding on an East-West link can be shown) is
shown below. Unnumbered interfaces are implicitly assumed and for
simplicity, the key value elements which may be included in their
South TIEs or North TIEs are not shown. First, in Figure 15 are the
TIEs generated by some nodes.
ToF 21 South TIEs:
Node South TIE:
NodeTIEElement(level=2,
neighbors(
(Spine 111, level 1, cost 1, links(...)),
(Spine 112, level 1, cost 1, links(...)),
(Spine 121, level 1, cost 1, links(...)),
(Spine 122, level 1, cost 1, links(...))
)
)
Prefix South TIE:
PrefixTIEElement(prefixes(0/0, metric 1), (::/0, metric 1))
Spine 111 South TIEs:
Node South TIE:
NodeTIEElement(level=1,
neighbors(
(ToF 21, level 2, cost 1, links(...)),
(ToF 22, level 2, cost 1, links(...)),
(Spine 112, level 1, cost 1, links(...)),
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(Leaf111, level 0, cost 1, links(...)),
(Leaf112, level 0, cost 1, links(...))
)
)
Prefix South TIE:
PrefixTIEElement(prefixes(0/0, metric 1), (::/0, metric 1))
Spine 111 North TIEs:
Node North TIE:
NodeTIEElement(level=1,
neighbors(
(ToF 21, level 2, cost 1, links(...)),
(ToF 22, level 2, cost 1, links(...)),
(Spine 112, level 1, cost 1, links(...)),
(Leaf111, level 0, cost 1, links(...)),
(Leaf112, level 0, cost 1, links(...))
)
)
Prefix North TIE:
PrefixTIEElement(prefixes(Spine 111.loopback)
Spine 121 South TIEs:
Node South TIE:
NodeTIEElement(level=1,
neighbors(
(ToF 21, level 2, cost 1, links(...)),
(ToF 22, level 2, cost 1, links(...)),
(Leaf121, level 0, cost 1, links(...)),
(Leaf122, level 0, cost 1, links(...))
)
)
Prefix South TIE:
PrefixTIEElement(prefixes(0/0, metric 1), (::/0, metric 1))
Spine 121 North TIEs:
Node North TIE:
NodeTIEElement(level=1,
neighbors(
(ToF 21, level 2, cost 1, links(...)),
(ToF 22, level 2, cost 1, links(...)),
(Leaf121, level 0, cost 1, links(...)),
(Leaf122, level 0, cost 1, links(...))
)
)
Prefix North TIE:
PrefixTIEElement(prefixes(Spine 121.loopback)
Leaf112 North TIEs:
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Node North TIE:
NodeTIEElement(level=0,
neighbors(
(Spine 111, level 1, cost 1, links(...)),
(Spine 112, level 1, cost 1, links(...))
)
)
Prefix North TIE:
PrefixTIEElement(prefixes(Leaf112.loopback, Prefix112, Prefix_MH))
Figure 15: Example TIEs Generated in a 2 Level Spine-and-Leaf
Topology
It may not be obvious here as to why the Node South TIEs contain all
the adjacencies of the corresponding node. This will be necessary
for algorithms further elaborated on in Section 6.3.9 and
Section 6.8.7.
For Node TIEs to carry more adjacencies than fit into an MTU-sized
packet, the element _neighbors_ may contain a different set of
neighbors in each TIE. Those disjointed sets of neighbors MUST be
joined during corresponding computation. However, if the following
occurs across multiple Node TIEs
1. _capabilities_ do not match *or*
2. _flags_ values do not match *or*
3. same neighbor repeats in multiple TIEs with different values
The implementation is expected to use the value of any of the valid
TIEs it received as it cannot control the arrival order of those
TIEs.
The _miscabled_links_ element SHOULD be included in every Node TIE,
otherwise the behavior is undefined.
A ToF node MUST include information on all other ToFs it is aware of
through reflection. The _same_plane_tofs_ element is used to carry
this information. To prevent MTU overrun problems, multiple Node
TIEs can carry disjointed sets of ToFs which MUST be joined to form a
single set.
Different TIE types are carried in _TIEElement_. Schema enum
`common.TIETypeType` in _TIEID_ indicates which elements MUST be
present in the _TIEElement_. In case of a mismatch between the
_TIETypeType_ in the _TIEID_ and the present element, the unexpected
elements MUST be ignored. In case of lack of expected element in the
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TIE an error MUST be reported and the TIE MUST be ignored. The
element _positive_disaggregation_prefixes_ and
_positive_external_disaggregation_prefixes_ MUST be advertised
southbound only and ignored in North TIEs. The element
_negative_disaggregation_prefixes_ MUST be propagated according to
Section 6.5.2 southwards towards lower levels to heal pathological
upper-level partitioning, otherwise traffic loss may occur in
multiplane fabrics. It MUST NOT be advertised within a North TIE and
MUST be ignored otherwise.
6.3.3. Flooding
As described before, TIEs themselves are transported over UDP with
the ports indicated in the LIE exchanges and using the destination
address on which the LIE adjacency has been formed.
TIEs are uniquely identified by the _TIEID_ schema element. The
_TIEID_ induces a total order achieved by comparing the elements in
sequence defined in the element and comparing each value as an
unsigned integer of corresponding length. The _TIEHeader_ element
contains a _seq_nr_ element to distinguish newer versions of same
TIE.
The TIEHEader can also carry an _origination_time_ schema element
(for fabrics that utilize precision timing) which contains the
absolute timestamp of when the TIE was generated and an
_origination_lifetime_ to indicate the original lifetime when the TIE
was generated. When carried, they can be used for debugging or
security purposes (e.g. to prevent lifetime modification attacks).
_remaining_lifetime_ counts down to 0 from _origination_lifetime_.
TIEs with lifetimes differing by less than _lifetime_diff2ignore_
MUST be considered EQUAL (if all other fields are equal). This
constant MUST be larger than _purge_lifetime_ to avoid
retransmissions.
This normative ordering methodology is described in Figure 16 and
MUST be used by all implementations.
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for each TIEPacket:
TIEHeader = TIEPacket.TIEHeader
TIEElement = TIEPacket.TIEElement
seq_nr = TIEHeader.seq_nr
TIEID = TIEHeader.TIEID
direction = TIEID.direction
# System ID
originator = TIEID.originator
# TIETypeType
tietype = TIEID.tietype
tie_nr = TIEID.tie_nr
if X.direction > Y.direction:
return X.direction
else if X.direction < Y.direction:
return Y.direction
else if X.originator > Y.originator:
return X.originator
else if X.originator < Y.originator:
return Y.originator
else:
if X.tietype == Y.tietype:
if X.tie_nr == Y.tie_nr:
if X.seq_nr == Y.seq_nr:
X.lifetime_left = X.remaining_lifetime - time since TIE was received
Y.lifetime_left = Y.remaining_lifetime - time since TIE was received
if absolute_value_of(X.lifetime_left - Y.lifetime_left) <= common.lifetime_diff2ignore:
return equal
else:
return TIE with largest lifetime_left
else:
return X.seq_nr compared to Y.seq_nr
else:
return X.tie_nr compared to Y.tie_nr
else:
return X.TIEType compared to Y.TIEType
Figure 16: TIE Ordering
All valid TIE types are defined in _TIETypeType_. This enum
indicates what TIE type the TIE is carrying. In case the value is
not known to the receiver, the TIE MUST be re-flooded with scope
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identical to the scope of a prefix TIE. This allows for future
extensions of the protocol within the same major schema with types
opaque to some nodes with some restrictions defined in Appendix B.
6.3.3.1. Normative Flooding Procedures
On reception of a TIE with an undefined level value in the packet
header the node MUST issue a warning and discard the packet.
This section specifies the precise, normative flooding mechanism and
can be omitted unless the reader is pursuing an implementation of the
protocol or looks for a deep understanding of underlying information
distribution mechanism.
Flooding Procedures are described in terms of the flooding state of
an adjacency and resulting operations on it driven by packet
arrivals. Implementations MUST implement a behavior that is
externally indistinguishable from the FSMs and normative procedures
given here.
RIFT does not specify any kind of flood rate limiting. To help with
adjustment of flooding speeds the encoded packets provide hints to
react accordingly to losses or overruns via
_you_are_sending_too_quickly_ in the _LIEPacket_ and `Packet Number`
in the security envelope described in Section 6.9.3. Flooding of all
corresponding topology exchange elements SHOULD be performed at the
highest feasible rate but the rate of transmission MUST be throttled
by reacting to packet elements and features of the system such as
e.g. queue lengths or congestion indications in the protocol packets.
A node SHOULD NOT send out any topology information elements if the
adjacency is not in a "ThreeWay" state. No further tightening of
this rule is possible. For example, link buffering may cause both
LIEs and TIEs/TIDEs/TIREs to be re-ordered.
A node MUST drop any received TIEs/TIDEs/TIREs unless it is in
_ThreeWay_ state.
TIEs generated by other nodes MUST be re-flooded. TIDEs and TIREs
MUST NOT be re-flooded.
6.3.3.1.1. FloodState Structure per Adjacency
The structure contains conceptually for each adjacency the following
elements. The word "collection" or "queue" indicates a set of
elements that can be iterated over:
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TIES_TX:
Collection containing all the TIEs to transmit on the adjacency.
TIES_ACK:
Collection containing all the TIEs that have to be acknowledged on
the adjacency.
TIES_REQ:
Collection containing all the TIE headers that have to be
requested on the adjacency.
TIES_RTX:
Collection containing all TIEs that need retransmission with the
corresponding time to retransmit.
FILTERED_TIEDB:
A filtered view of TIEDB, which retains for consideration only
those headers permitted by is_tide_entry_filtered and which either
have a lifetime left > 0 or have no content.
Following words are used for well-known elements and procedures
operating on this structure:
TIE:
Describes either a full RIFT TIE or just the _TIEHeader_ or
_TIEID_ equivalent as defined in Appendix B.3. The corresponding
meaning is unambiguously contained in the context of each
algorithm.
is_flood_reduced(TIE):
returns whether a TIE can be flood reduced or not.
is_tide_entry_filtered(TIE):
returns whether a header should be propagated in TIDE according to
flooding scopes.
is_request_filtered(TIE):
returns whether a TIE request should be propagated to neighbor or
not according to flooding scopes.
is_flood_filtered(TIE):
returns whether a TIE requested be flooded to neighbor or not
according to flooding scopes.
try_to_transmit_tie(TIE):
A. if not is_flood_filtered(TIE) then
1. remove TIE from TIES_RTX if present
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2. if TIE with same key is found on TIES_ACK then
a. if TIE is same or newer than TIE do nothing else
b. remove TIE from TIES_ACK and add TIE to TIES_TX
3. else insert TIE into TIES_TX
ack_tie(TIE):
remove TIE from all collections and then insert TIE into TIES_ACK.
tie_been_acked(TIE):
remove TIE from all collections.
remove_from_all_queues(TIE):
same as _tie_been_acked_.
request_tie(TIE):
if not is_request_filtered(TIE) then remove_from_all_queues(TIE)
and add to TIES_REQ.
move_to_rtx_list(TIE):
remove TIE from TIES_TX and then add to TIES_RTX using TIE
retransmission interval.
clear_requests(TIEs):
remove all TIEs from TIES_REQ.
bump_own_tie(TIE):
for self-originated TIE originate an empty or re-generate with
version number higher than the one in TIE.
The collection SHOULD be served with the following priorities if the
system cannot process all the collections in real time:
1. Elements on TIES_ACK should be processed with highest priority
2. TIES_TX
3. TIES_REQ and TIES_RTX should be processed with lowest priority
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6.3.3.1.2. TIDEs
_TIEID_ and _TIEHeader_ space forms a strict total order (modulo
incomparable sequence numbers as explained in Appendix A in the very
unlikely event that can occur if a TIE is "stuck" in a part of a
network while the originator reboots and reissues TIEs many times to
the point its sequence# rolls over and forms incomparable distance to
the "stuck" copy) which implies that a comparison relation is
possible between two elements. With that it is implicitly possible
to compare TIEs, TIEHeaders and TIEIDs to each other whereas the
shortest viable key is always implied.
6.3.3.1.2.1. TIDE Generation
As given by timer constant, periodically generate TIDEs by:
NEXT_TIDE_ID: ID of next TIE to be sent in TIDE.
a. NEXT_TIDE_ID = MIN_TIEID
b. while NEXT_TIDE_ID not equal to MAX_TIEID do
1. HEADERS = Exactly TIRDEs_PER_PKT headers from FILTERED_TIEDB
starting at NEXT_TIDE_ID, unless fewer than TIRDEs_PER_PKT
remain, in which case all remaining headers.
2. if HEADERS is empty then START = MIN_TIEID else START = first
element in HEADERS
3. if HEADERS' size less than TIRDEs_PER_PKT then END =
MAX_TIEID else END = last element in HEADERS
4. send *sorted* HEADERS as TIDE setting START and END as its
range
5. NEXT_TIDE_ID = END
The constant _TIRDEs_PER_PKT_ SHOULD be computed per interface and
used by the implementation to limit the amount of TIE headers per
TIDE so the sent TIDE PDU does not exceed interface MTU.
TIDE PDUs SHOULD be spaced on sending to prevent packet drops.
The algorithm will intentionally enter the loop once and send a
single TIDE even when the database is empty, otherwise no TIDEs would
be sent for in case of empty database and break intended
synchronization.
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6.3.3.1.2.2. TIDE Processing
On reception of TIDEs the following processing is performed:
TXKEYS: Collection of TIE Headers to be sent after processing of
the packet
REQKEYS: Collection of TIEIDs to be requested after processing of
the packet
CLEARKEYS: Collection of TIEIDs to be removed from flood state
queues
LASTPROCESSED: Last processed TIEID in TIDE
DBTIE: TIE in the Link State Database (LSDB) if found
a. LASTPROCESSED = TIDE.start_range
b. for every HEADER in TIDE do
1. DBTIE = find HEADER in current LSDB
2. if HEADER < LASTPROCESSED then report error and reset
adjacency and return
3. put all TIEs in LSDB where (TIE.HEADER > LASTPROCESSED and
TIE.HEADER < HEADER) into TXKEYS
4. LASTPROCESSED = HEADER
5. if DBTIE not found then
I) if originator is this node, then bump_own_tie
II) else put HEADER into REQKEYS
6. if DBTIE.HEADER < HEADER then
I) if originator is this node then bump_own_tie else
i. if this is a North TIE header from a northbound
neighbor then override DBTIE in LSDB with HEADER
ii. else put HEADER into REQKEYS
7. if DBTIE.HEADER > HEADER then put DBTIE.HEADER into TXKEYS
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8. if DBTIE.HEADER = HEADER then
I) if DBTIE has content already then put DBTIE.HEADER into
CLEARKEYS
II) else put HEADER into REQKEYS
c. put all TIEs in LSDB where (TIE.HEADER > LASTPROCESSED and
TIE.HEADER <= TIDE.end_range) into TXKEYS
d. for all TIEs in TXKEYS try_to_transmit_tie(TIE)
e. for all TIEs in REQKEYS request_tie(TIE)
f. for all TIEs in CLEARKEYS remove_from_all_queues(TIE)
6.3.3.1.3. TIREs
6.3.3.1.3.1. TIRE Generation
Elements from both TIES_REQ and TIES_ACK MUST be collected and sent
out as fast as feasible as TIREs. When sending TIREs with elements
from TIES_REQ the _remaining_lifetime_ field in
_TIEHeaderWithLifeTime_ MUST be set to 0 to force reflooding from the
neighbor even if the TIEs seem to be same.
6.3.3.1.3.2. TIRE Processing
On reception of TIREs the following processing is performed:
TXKEYS: Collection of TIE Headers to be send after processing of
the packet
REQKEYS: Collection of TIEIDs to be requested after processing of
the packet
ACKKEYS: Collection of TIEIDs that have been acked
DBTIE: TIE in the LSDB if found
a. for every HEADER in TIRE do
1. DBTIE = find HEADER in current LSDB
2. if DBTIE not found then do nothing
3. if DBTIE.HEADER < HEADER then put HEADER into REQKEYS
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4. if DBTIE.HEADER > HEADER then put DBTIE.HEADER into TXKEYS
5. if DBTIE.HEADER = HEADER then put DBTIE.HEADER into ACKKEYS
b. for all TIEs in TXKEYS try_to_transmit_tie(TIE)
c. for all TIEs in REQKEYS request_tie(TIE)
d. for all TIEs in ACKKEYS tie_been_acked(TIE)
6.3.3.1.4. TIEs Processing on Flood State Adjacency
On reception of TIEs the following processing is performed:
ACKTIE: TIE to acknowledge
TXTIE: TIE to transmit
DBTIE: TIE in the LSDB if found
a. DBTIE = find TIE in current LSDB
b. if DBTIE not found then
1. if originator is this node then bump_own_tie with a short
remaining lifetime
2. else insert TIE into LSDB and ACKTIE = TIE
else
1. if DBTIE.HEADER = TIE.HEADER then
i. if DBTIE has content already then ACKTIE = TIE
ii. else process like the "DBTIE.HEADER < TIE.HEADER" case
2. if DBTIE.HEADER < TIE.HEADER then
i. if originator is this node then bump_own_tie
ii. else insert TIE into LSDB and ACKTIE = TIE
3. if DBTIE.HEADER > TIE.HEADER then
i. if DBTIE has content already then TXTIE = DBTIE
ii. else ACKTIE = DBTIE
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c. if TXTIE is set then try_to_transmit_tie(TXTIE)
d. if ACKTIE is set then ack_tie(TIE)
6.3.3.1.5. Sending TIEs
On a periodic basis all TIEs with lifetime left > 0 MUST be sent out
on the adjacency, removed from TIES_TX list and requeued onto
TIES_RTX list. The specific period is out of scope for this
document.
6.3.3.1.6. TIEs Processing In LSDB
The Link State Database (LSDB) holds the most recent copy of TIEs
received via flooding from according peers. Consecutively, after
version tie-breaking by LSDB, a peer receives from the LSDB the
newest versions of TIEs received by other peers and processes them
(without any filtering) just like receiving TIEs from its remote
peer. Such a publisher model can be implemented in several ways,
either in a single thread of execution or in multiple parallel
threads.
LSDB can be logically considered as the entity aging out TIEs, i.e.
being responsible to discard TIEs that are stored longer than
_remaining_lifetime_ on their reception.
LSDB is also expected to periodically re-originate the node's own
TIEs. Originating at an interval significantly shorter than
_default_lifetime_ is RECOMMENDED to prevent TIE expiration by other
nodes in the network which can lead to instabilities.
6.3.4. TIE Flooding Scopes
In a somewhat analogous fashion to link-local, area and domain
flooding scopes, RIFT defines several complex "flooding scopes"
depending on the direction and type of TIE propagated.
Every North TIE is flooded northbound, providing a node at a given
level with the complete topology of the Clos or Fat Tree network that
is reachable southwards of it, including all specific prefixes. This
means that a packet received from a node at the same or lower level
whose destination is covered by one of those specific prefixes will
be routed directly towards the node advertising that prefix rather
than sending the packet to a node at a higher level.
A node's Node South TIEs, consisting of all node's adjacencies and
prefix South TIEs limited to those related to default IP prefix and
disaggregated prefixes, are flooded southbound in order to inform
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nodes one level down of connectivity of the higher level as well as
reachability to the rest of the fabric. In order to allow an E-W
disconnected node in a given level to receive the South TIEs of other
nodes at its level, every *NODE* South TIE is "reflected" northbound
to the level from which it was received. It should be noted that
East-West links are included in South TIE flooding (except at the ToF
level); those TIEs need to be flooded to satisfy algorithms in
Section 6.4. In that way nodes at same level can learn about each
other using without a lower level except in case of leaf level. The
precise, normative flooding scopes are given in Table 3. Those rules
also govern what SHOULD be included in TIDEs on the adjacency.
Again, East-West flooding scopes are identical to South flooding
scopes except in case of ToF East-West links (rings) which are
basically performing northbound flooding.
Node South TIE "south reflection" enables support of positive
disaggregation on failures as described in in Section 6.5 and
flooding reduction in Section 6.3.9.
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+===========+======================+==============+=================+
| Type / | South | North | East-West |
| Direction | | | |
+===========+======================+==============+=================+
| Node | flood if level of | flood if | flood only if |
| South TIE | originator is | level of | this node is |
| | equal to this | originator | not ToF |
| | node | is higher | |
| | | than this | |
| | | node | |
+-----------+----------------------+--------------+-----------------+
| non-Node | flood self- | flood only | flood only if |
| South TIE | originated only | if neighbor | self-originated |
| | | is | and this node |
| | | originator | is not ToF |
| | | of TIE | |
+-----------+----------------------+--------------+-----------------+
| all North | never flood | flood always | flood only if |
| TIEs | | | this node is |
| | | | ToF |
+-----------+----------------------+--------------+-----------------+
| TIDE | include at least | include at | if this node is |
| | all non-self | least all | ToF then |
| | originated North | Node South | include all |
| | TIE headers and | TIEs and all | North TIEs, |
| | self-originated | South TIEs | otherwise only |
| | South TIE headers | originated | self-originated |
| | and Node South | by peer and | TIEs |
| | TIEs of nodes at | all North | |
| | same level | TIEs | |
+-----------+----------------------+--------------+-----------------+
| TIRE as | request all North | request all | if this node is |
| Request | TIEs and all | South TIEs | ToF then apply |
| | peer's self- | | North scope |
| | originated TIEs | | rules, |
| | and all Node | | otherwise South |
| | South TIEs | | scope rules |
+-----------+----------------------+--------------+-----------------+
| TIRE as | Ack all received | Ack all | Ack all |
| Ack | TIEs | received | received TIEs |
| | | TIEs | |
+-----------+----------------------+--------------+-----------------+
Table 3: Normative Flooding Scopes
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If the TIDE includes additional TIE headers beside the ones
specified, the receiving neighbor must apply the corresponding filter
to the received TIDE strictly and MUST NOT request the extra TIE
headers that were not allowed by the flooding scope rules in its
direction.
To illustrate these rules, consider using the topology in Figure 2,
with the optional link between spine 111 and spine 112, and the
associated TIEs given in Figure 15. The flooding from particular
nodes of the TIEs is given in Table 4.
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+============+==========+===========================================+
| Local | Neighbor | TIEs Flooded from Local to Neighbor Node |
| Node | Node | |
+============+==========+===========================================+
| Leaf111 | Spine | Leaf111 North TIEs, Spine 111 Node South |
| | 112 | TIE |
+------------+----------+-------------------------------------------+
| Leaf111 | Spine | Leaf111 North TIEs, Spine 112 Node South |
| | 111 | TIE |
+------------+----------+-------------------------------------------+
| ... | ... | ... |
+------------+----------+-------------------------------------------+
| Spine | Leaf111 | Spine 111 South TIEs |
| 111 | | |
+------------+----------+-------------------------------------------+
| Spine | Leaf112 | Spine 111 South TIEs |
| 111 | | |
+------------+----------+-------------------------------------------+
| Spine | Spine | Spine 111 South TIEs |
| 111 | 112 | |
+------------+----------+-------------------------------------------+
| Spine | ToF 21 | Spine 111 North TIEs, Leaf111 North TIEs, |
| 111 | | Leaf112 North TIEs, ToF 22 Node South TIE |
+------------+----------+-------------------------------------------+
| Spine | ToF 22 | Spine 111 North TIEs, Leaf111 North TIEs, |
| 111 | | Leaf112 North TIEs, ToF 21 Node South TIE |
+------------+----------+-------------------------------------------+
| ... | ... | ... |
+------------+----------+-------------------------------------------+
| ToF 21 | Spine | ToF 21 South TIEs |
| | 111 | |
+------------+----------+-------------------------------------------+
| ToF 21 | Spine | ToF 21 South TIEs |
| | 112 | |
+------------+----------+-------------------------------------------+
| ToF 21 | Spine | ToF 21 South TIEs |
| | 121 | |
+------------+----------+-------------------------------------------+
| ToF 21 | Spine | ToF 21 South TIEs |
| | 122 | |
+------------+----------+-------------------------------------------+
| ... | ... | ... |
+------------+----------+-------------------------------------------+
Table 4: Flooding some TIEs from example topology
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6.3.5. RAIN: RIFT Adjacency Inrush Notification
The optional RIFT Adjacency Inrush Notification (RAIN) mechanism
helps to prevent adjacencies from being overwhelmed by flooding on
restart or bring-up with many southbound neighbors. A node MAY set
in its LIEs the corresponding _you_are_sending_too_quickly_ flag to
indicate to the neighbor that it SHOULD flood Node TIEs with normal
speed and significantly slow down the flooding of any other TIEs.
The flag SHOULD be set only in the southbound direction. The
receiving node SHOULD accommodate the request to lessen the flooding
load on the affected node if south of the sender and should ignore
the indication if north of the sender.
The distribution of Node TIEs at normal speed even at high load
guarantees correct behavior of algorithms like disaggregation or
default route origination. Furthermore though, the use of this bit
presents an inherent trade-off between processing load and
convergence speed since significantly slowing down flooding of
northbound prefixes from neighbors for an extended time will lead to
traffic losses.
6.3.6. Initial and Periodic Database Synchronization
The initial exchange of RIFT includes periodic TIDE exchanges that
contain description of the link state database and TIREs which
perform the function of requesting unknown TIEs as well as confirming
reception of flooded TIEs. The content of TIDEs and TIREs is
governed by Table 3.
6.3.7. Purging and Roll-Overs
When a node exits the network, if "unpurged", residual stale TIEs may
exist in the network until their lifetimes expire (which in case of
RIFT is by default a rather long period to prevent ongoing re-
origination of TIEs in very large topologies). RIFT does not have a
"purging mechanism" based on sending specialized "purge" packets. In
other routing protocols such a mechanism has proven to be complex and
fragile based on many years of experience. RIFT simply issues a new,
i.e., higher sequence number, empty version of the TIE with a short
lifetime given by the _purge_lifetime_ constant and relies on each
node to age out and delete each TIE copy independently. Abundant
amounts of memory are available today even on low-end platforms and
hence keeping those relatively short-lived extra copies for a while
is acceptable. The information will age out and in the meantime all
computations will deliver correct results if a node leaves the
network due to the new information distributed by its adjacent nodes
breaking bi-directional connectivity checks in different
computations.
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Once a RIFT node issues a TIE with an ID, it SHOULD preserve the ID
as long as feasible (also when the protocol restarts), even if the
TIE looses all content. The re-advertisement of an empty TIE
fulfills the purpose of purging any information advertised in
previous versions. The originator is free to not re-originate the
corresponding empty TIE again or originate an empty TIE with
relatively short lifetime to prevent large number of long-lived empty
stubs polluting the network. Each node MUST timeout and clean up the
corresponding empty TIEs independently.
Upon restart a node MUST be prepared to receive TIEs with its own
System ID and supersede them with equivalent, newly generated, empty
TIEs with a higher sequence number. As above, the lifetime can be
relatively short since it only needs to exceed the necessary
propagation and processing delay by all the nodes that are within the
TIE's flooding scope.
TIE sequence numbers are rolled over using the method described in
Appendix A. First sequence number of any spontaneously originated
TIE (i.e. not originated to override a detected older copy in the
network) MUST be a reasonably unpredictable random number (for
example [RFC4086]) in the interval [0, 2^30-1] which will prevent
otherwise identical TIE headers to remain "stuck" in the network with
content different from TIE originated after reboot. In traditional
link-state protocols this is delegated to a 16-bit checksum on packet
content. RIFT avoids this design due to the CPU burden presented by
computation of such checksums and additional complications tied to
the fact that the checksum must be "patched" into the packet after
the generation of the content, a difficult proposition in binary
hand-crafted formats already and highly incompatible with model-
based, serialized formats. The sequence number space is hence
consciously chosen to be 64-bits wide to make the occurrence of a TIE
with same sequence number but different content as much or even more
unlikely than the checksum method. To emulate the "checksum
behavior" an implementation could choose to compute a 64-bit checksum
or hash function over the TIE content and use that as part of the
first sequence number after reboot.
6.3.8. Southbound Default Route Origination
Under certain conditions nodes issue a default route in their South
Prefix TIEs with costs as computed in Section 6.8.7.1.
A node X that
1. is *not* overloaded *and*
2. has southbound or East-West adjacencies
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SHOULD originate in its south prefix TIE such a default route if and
only if
1. all other nodes at X's' level are overloaded *or*
2. all other nodes at X's' level have NO northbound adjacencies *or*
3. X has computed reachability to a default route during N-SPF.
The term "all other nodes at X's' level" describes obviously just the
nodes at the same level in the PoD with a viable lower level
(otherwise the Node South TIEs cannot be reflected. The nodes in PoD
1 and PoD 2 are "invisible" to each other).
A node originating a southbound default route SHOULD install a
default discard route if it did not compute a default route during
N-SPF. This basically means that the top of the fabric will drop
traffic for unreachable addresses.
6.3.9. Northbound TIE Flooding Reduction
RIFT chooses only a subset of northbound nodes to propagate flooding
and with that both balances it (to prevent 'hot' flooding links)
across the fabric as well as reduces its volume. The solution is
based on several principles:
1. a node MUST flood self-originated North TIEs to all the reachable
nodes at the level above which is called the node's "parents";
2. it is typically not necessary that all parents reflood the North
TIEs to achieve a complete flooding of all the reachable nodes
two levels above which we call the node's "grandparents";
3. to control the volume of its flooding two hops North and yet keep
it robust enough, it is advantageous for a node to select a
subset of its parents as "Flood Repeaters" (FRs), which combined
together deliver two or more copies of its flooding to all of its
parents, i.e. the originating node's grandparents;
4. nodes at the same level do *not* have to agree on a specific
algorithm to select the FRs, but overall load balancing should be
achieved so that different nodes at the same level should tend to
select different parents as FRs;
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5. there are usually many solutions to the problem of finding a set
of FRs for a given node; the problem of finding the minimal set
is (similar to) a NP-Complete problem and a globally optimal set
may not be the minimal one if load-balancing with other nodes is
an important consideration;
6. it is expected that there will often exist sets of equivalent
nodes at a level L, defined as having a common set of parents at
L+1. Applying this observation at both L and L+1, an algorithm
may attempt to split the larger problem in a sum of smaller
separate problems;
7. it is expected that there will be from time to time a broken link
between a parent and a grandparent, and in that case the parent
is probably a poor FR due to its lower reliability. An algorithm
may attempt to eliminate parents with broken northbound
adjacencies first in order to reduce the number of FRs. Albeit
it could be argued that relying on higher fanout FRs will slow
flooding due to higher replication, load reliability of FR's
links is likely a more pressing concern.
In a fully connected Clos Network, this means that a node selects one
arbitrary parent as FR and then a second one for redundancy. The
computation can be relatively simple and completely distributed
without any need for synchronization amongst nodes. In a "PoD"
structure, where the Level L+2 is partitioned into silos of
equivalent grandparents that are only reachable from respective
parents, this means treating each silo as a fully connected Clos
Network and solving the problem within the silo.
In terms of signaling, a node has enough information to select its
set of FRs; this information is derived from the node's parents' Node
South TIEs, which indicate the parent's reachable northbound
adjacencies to its own parents (the node's grandparents). A node may
send a LIE to a northbound neighbor with the optional boolean field
_you_are_flood_repeater_ set to false, to indicate that the
northbound neighbor is not a flood repeater for the node that sent
the LIE. In that case the northbound neighbor SHOULD NOT reflood
northbound TIEs received from the node that sent the LIE. If the
_you_are_flood_repeater_ is absent or if _you_are_flood_repeater_ is
set to true, then the northbound neighbor is a flood repeater for the
node that sent the LIE and MUST reflood northbound TIEs received from
that node. The element _you_are_flood_repeater_ MUST be ignored if
received from a northbound adjacency.
This specification provides a simple default algorithm that SHOULD be
implemented and used by default on every RIFT node.
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* let |NA(Node) be the set of Northbound adjacencies of node Node
and CN(Node) be the cardinality of |NA(Node);
* let |SA(Node) be the set of Southbound adjacencies of node Node
and CS(Node) be the cardinality of |SA(Node);
* let |P(Node) be the set of node Node's parents;
* let |G(Node) be the set of node Node's grandparents. Observe
that |G(Node) = |P(|P(Node));
* let N be the child node at level L computing a set of FR;
* let P be a node at level L+1 and a parent node of N, i.e. bi-
directionally reachable over adjacency ADJ(N, P);
* let G be a grandparent node of N, reachable transitively via a
parent P over adjacencies ADJ(N, P) and ADJ(P, G). Observe that N
does not have enough information to check bidirectional
reachability of ADJ(P, G);
* let R be a redundancy constant integer; a value of 2 or higher for
R is RECOMMENDED;
* let S be a similarity constant integer; a value in range 0 .. 2
for S is RECOMMENDED, the value of 1 SHOULD be used. Two
cardinalities are considered as equivalent if their absolute
difference is less than or equal to S, i.e. |a-b|<=S.
* let RND be a 64-bit random number (for example [RFC4086])
generated by the system once on startup.
The algorithm consists of the following steps:
1. Derive a 64-bits number by XOR'ing 'N's System ID with RND.
2. Derive a 16-bits pseudo-random unsigned integer PR(N) from the
resulting 64-bits number by splitting it in 16-bits-long words
W1, W2, W3, W4 (where W1 are the least significant 16 bits of the
64-bits number, and W4 are the most significant 16 bits) and then
XOR'ing the circularly shifted resulting words together:
A. (W1<<1) xor (W2<<2) xor (W3<<3) xor (W4<<4);
where << is the circular shift operator.
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3. Sort the parents by decreasing number of northbound adjacencies
(using decreasing System ID of the parent as tie-breaker):
sort |P(N) by decreasing CN(P), for all P in |P(N), as ordered
array |A(N)
4. Partition |A(N) in subarrays |A_k(N) of parents with equivalent
cardinality of northbound adjacencies (in other words with
equivalent number of grandparents they can reach):
A. set k=0; // k is the ID of the subarrray
B. set i=0;
C. while i < CN(N) do
i) set j=i;
ii) while i < CN(N) and CN(|A(N)[j]) - CN(|A(N)[i]) <= S
a. place |A(N)[i] in |A_k(N) // abstract action, maybe
noop
b. set i=i+1;
iii) /* At this point j is the index in |A(N) of the first
member of |A_k(N) and (i-j) is C_k(N) defined as the
cardinality of |A_k(N) */
set k=k+1;
/* At this point k is the total number of subarrays, initialized
for the shuffling operation below */
5. shuffle individually each subarrays |A_k(N) of cardinality C_k(N)
within |A(N) using the Durstenfeld variation of Fisher-Yates
algorithm that depends on N's System ID:
A. while k > 0 do
i) for i from C_k(N)-1 to 1 decrementing by 1 do
a. set j to PR(N) modulo i;
b. exchange |A_k[j] and |A_k[i];
ii) set k=k-1;
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6. For each grandparent G, initialize a counter c(G) with the number
of its south-bound adjacencies to elected flood repeaters (which
is initially zero):
A. for each G in |G(N) set c(G) = 0;
7. Finally keep as FRs only parents that are needed to maintain the
number of adjacencies between the FRs and any grandparent G equal
or above the redundancy constant R:
A. for each P in reshuffled |A(N);
i) if there exists an adjacency ADJ(P, G) in |NA(P) such
that c(G) < R then
a. place P in FR set;
b. for all adjacencies ADJ(P, G') in |NA(P) increment
c(G')
B. If any c(G) is still < R, it was not possible to elect a set
of FRs that covers all grandparents with redundancy R
Additional rules for flooding reduction:
1. The algorithm MUST be re-evaluated by a node on every change of
local adjacencies or reception of a parent South TIE with changed
adjacencies. A node MAY apply a hysteresis to prevent excessive
amount of computation during periods of network instability just
like in the case of reachability computation.
2. Upon a change of the flood repeater set, a node SHOULD send out
LIEs that grant flood repeater status to newly promoted nodes
before it sends LIEs that revoke the status to the nodes that
have been newly demoted. This is done to prevent transient
behavior where the full coverage of grandparents is not
guaranteed. Such a condition is sometimes unavoidable in case of
lost LIEs but it will correct itself though at possible transient
reduction in flooding propagation speeds. The election can use
the LIE FSM _FloodLeadersChanged_ event to notify LIE FSMs of
necessity to update the sent LIEs.
3. A node MUST always flood its self-originated TIEs to all its
neighbors.
4. A node receiving a TIE originated by a node for which it is not a
flood repeater SHOULD NOT reflood such TIEs to its neighbors
except for rules in Section 6.3.9, Paragraph 10, Item 6.
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5. The indication of flood reduction capability MUST be carried in
the Node TIEs in the _flood_reduction_ element and MAY be used to
optimize the algorithm to account for nodes that will flood
regardless.
6. A node generates TIDEs as usual but when receiving TIREs or TIDEs
resulting in requests for a TIE of which the newest received copy
came on an adjacency where the node was not flood repeater it
SHOULD ignore such requests on first and only first request.
Normally, the nodes that received the TIEs as flooding repeaters
should satisfy the requesting node and with that no further TIREs
for such TIEs will be generated. Otherwise, the next set of
TIDEs and TIREs MUST lead to flooding independent of the flood
repeater status. This solves a very difficult incast problem on
nodes restarting with a very wide fanout, especially northbound.
To retrieve the full database they often end up processing many
in-rushing copies whereas this approach load-balances the
incoming database between adjacent nodes and flood repeaters and
should guarantee that two copies are sent by different nodes to
ensure against any losses.
6.3.10. Special Considerations
First, due to the distributed, asynchronous nature of ZTP, it can
create temporary convergence anomalies where nodes at higher levels
of the fabric temporarily become lower than where they ultimately
belong. Since flooding can begin before ZTP is "finished" and in
fact must do so given there is no global termination criteria for the
unsychronized ZTP algorithm, information may end up temporarily in
wrong layers. A special clause when changing level takes care of
that.
More difficult is a condition where a node (e.g. a leaf) floods a TIE
north towards its grandparent, then its parent reboots, partitioning
the grandparent from leaf directly and then the leaf itself reboots.
That can leave the grandparent holding the "primary copy" of the
leaf's TIE. Normally this condition is resolved easily by the leaf
re-originating its TIE with a higher sequence number than it notices
in the northbound TIEs, here however, when the parent comes back it
won't be able to obtain leaf's North TIE from the grandparent easily
and with that the leaf may not issue the TIE with a higher sequence
number that can reach the grandparent for a long time. Flooding
procedures are extended to deal with the problem by the means of
special clauses that override the database of a lower level with
headers of newer TIEs received in TIDEs coming from the north. Those
headers are then propagated southbound towards the leaf to cause it
to originate a higher sequence number of the TIE effectively
refreshing it all the way up to ToF.
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6.4. Reachability Computation
A node has three possible sources of relevant information for
reachability computation. A node knows the full topology south of it
from the received North Node TIEs or alternately north of it from the
South Node TIEs. A node has the set of prefixes with their
associated distances and bandwidths from corresponding prefix TIEs.
To compute prefix reachability, a node runs conceptually a northbound
and a southbound SPF. N-SPF and S-SPF notation denotes here the
direction in which the computation front is progressing.
Since neither computation can "loop", it is possible to compute non-
equal-cost or even k-shortest paths [EPPSTEIN] and "saturate" the
fabric to the extent desired. This specification however uses
simple, familiar SPF algorithms and concepts as example due to their
prevalence in today's routing.
For reachability computation purposes, RIFT considers all parallel
links between two nodes to be of the same cost advertised in the
_cost_ element of _NodeNeighborsTIEElement_. In case the neighbor has
multiple parallel links at different cost, the largest distance
(highest numerical value) MUST be advertised. Given the range of
thrift encodings, _infinite_distance_ is defined as the largest non-
negative _MetricType_. Any link with metric larger than that (i.e.
negative MetricType) MUST be ignored in computations. Any link with
metric set to _invalid_distance_ MUST also be ignored in computation.
In case of a negatively distributed prefix the metric attribute MUST
be set to _infinite_distance_ by the originator and it MUST be
ignored by all nodes during computation except for the purpose of
determining transitive propagation and building the corresponding
routing table.
A prefix can carry the _directly_attached_ attribute to indicate that
the prefix is directly attached, i.e., should be routed to even if
the node is in overload. In case of a negatively distributed prefix
this attribute MUST not be included by the originator and it MUST be
ignored by all nodes during SPF computation. If a prefix is locally
originated the attribute _from_link_ can indicate the interface to
which the address belongs to. In case of a negatively distributed
prefix this attribute MUST NOT be included by the originator and it
MUST be ignored by all nodes during computation. A prefix can also
carry the _loopback_ attribute to indicate the said property.
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Prefixes are carried in different types of TIEs indicating their
type. For same prefix being included in different TIE types tie-
breaking is performed according to Section 6.8.1. If the same prefix
is included multiple times in multiple TIEs of the same type
originating at the same node the resulting behavior is unspecified.
6.4.1. Northbound Reachability SPF
N-SPF MUST use exclusively northbound and East-West adjacencies in
the computing node's node North TIEs (since if the node is a leaf it
may not have generated a Node South TIE) when starting SPF. Observe
that N-SPF is really just a one hop variety since Node South TIEs are
not re-flooded southbound beyond a single level (or East-West) and
with that the computation cannot progress beyond adjacent nodes.
Once progressing, the computation uses the next higher level's Node
South TIEs to find corresponding adjacencies to verify backlink
connectivity. Two unidirectional links MUST be associated together
to confirm bidirectional connectivity, a process often known as
`backlink check`. As part of the check, both Node TIEs MUST contain
the correct System IDs *and* expected levels.
The default route found when crossing an E-W link SHOULD be used if
and only if
1. the node itself does *not* have any northbound adjacencies *and*
2. the adjacent node has one or more northbound adjacencies
This rule forms a "one-hop default route split-horizon" and prevents
looping over default routes while allowing for "one-hop protection"
of nodes that lost all northbound adjacencies except at the ToF where
the links are used exclusively to flood topology information in
multi-plane designs.
Other south prefixes found when crossing E-W link MAY be used if and
only if
1. no north neighbors are advertising same or a supersuming non-
default prefix *and*
2. the node does not originate a non-default supersuming prefix
itself.
I.e., the E-W link can be used as a gateway of last resort for a
specific prefix only. Using south prefixes across E-W link can be
beneficial e.g., on automatic disaggregation in pathological fabric
partitioning scenarios.
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A detailed example can be found in Section 7.4.
6.4.2. Southbound Reachability SPF
S-SPF MUST use the southbound adjacencies in the Node South TIEs
exclusively, i.e. progresses towards nodes at lower levels. Observe
that E-W adjacencies are NEVER used in this computation. This
enforces the requirement that a packet traversing in a southbound
direction must never change its direction.
S-SPF MUST use northbound adjacencies in node North TIEs to verify
backlink connectivity by checking for presence of the link beside
correct System ID and level.
6.4.3. East-West Forwarding Within a non-ToF Level
Using south prefixes over horizontal links MAY occur if the N-SPF
includes East-West adjacencies in computation. It can protect
against pathological fabric partitioning cases that leave only paths
to destinations that would necessitate multiple changes of forwarding
direction between north and south.
6.4.4. East-West Links Within ToF Level
E-W ToF links behave in terms of flooding scopes defined in
Section 6.3.4 like northbound links and MUST be used exclusively for
control plane information flooding. Even though a ToF node could be
tempted to use those links during southbound SPF and carry traffic
over them this MUST NOT be attempted since it may, in anycast cases,
lead to routing loops. An implementation MAY try to resolve the
looping problem by following on the ring strictly tie-broken
shortest-paths only but the details are outside this specification.
And even then, the problem of proper capacity provisioning of such
links when they become traffic-bearing in case of failures is vexing
and when used for forwarding purposes, they defeat statistical non-
blocking guarantees that Clos is providing normally.
6.5. Automatic Disaggregation on Link & Node Failures
6.5.1. Positive, Non-transitive Disaggregation
Under normal circumstances, a node's South TIEs contain just the
adjacencies and a default route. However, if a node detects that its
default IP prefix covers one or more prefixes that are reachable
through it but not through one or more other nodes at the same level,
then it MUST explicitly advertise those prefixes in a South TIE.
Otherwise, some percentage of the northbound traffic for those
prefixes would be sent to nodes without corresponding reachability,
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causing it to be dropped. Even when traffic is not being dropped,
the resulting forwarding could 'backhaul' packets through the higher
level spines, clearly an undesirable condition affecting the blocking
probabilities of the fabric.
This specification refers to the process of advertising additional
prefixes southbound as 'positive disaggregation'. Such
disaggregation is non-transitive, i.e., its' effects are always
constrained to a single level of the fabric. Naturally, multiple
node or link failures can lead to several independent instances of
positive disaggregation necessary to prevent looping or bow-tying the
fabric.
A node determines the set of prefixes needing disaggregation using
the following steps:
1. A DAG computation in the southern direction is performed first.
The North TIEs are used to find all of prefixes it can reach and
the set of next-hops in the lower level for each of them. Such a
computation can be easily performed on a Fat Tree by setting all
link costs in the southern direction to 1 and all northern
directions to infinity. We term set of those prefixes |R, and
for each prefix, r, in |R, its set of next-hops is defined to
be |H(r).
2. The node uses reflected South TIEs to find all nodes at the same
level in the same PoD and the set of southbound adjacencies for
each. The set of nodes at the same level is termed |N and for
each node, n, in |N, its set of southbound adjacencies is defined
to be |A(n).
3. For a given r, if the intersection of |H(r) and |A(n), for any n,
is empty then that prefix r must be explicitly advertised by the
node in a South TIE.
4. Identical set of disaggregated prefixes is flooded on each of the
node's southbound adjacencies. In accordance with the normal
flooding rules for a South TIE, a node at the lower level that
receives this South TIE SHOULD NOT propagate it south-bound or
reflect the disaggregated prefixes back over its adjacencies to
nodes at the level from which it was received.
To summarize the above in simplest terms: if a node detects that its
default route encompasses prefixes for which one of the other nodes
in its level has no possible next-hops in the level below, it has to
disaggregate it to prevent traffic loss or suboptimal routing through
such nodes. Hence a node X needs to determine if it can reach a
different set of south neighbors than other nodes at the same level,
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which are connected to it via at least one common south neighbor. If
it can, then prefix disaggregation may be required. If it can't,
then no prefix disaggregation is needed. An example of
disaggregation is provided in Section 7.3.
Finally, a possible algorithm is described here:
1. Create partial_neighbors = (empty), a set of neighbors with
partial connectivity to the node X's level from X's perspective.
Each entry in the set is a south neighbor of X and a list of
nodes of X.level that can't reach that neighbor.
2. A node X determines its set of southbound neighbors
X.south_neighbors.
3. For each South TIE originated from a node Y that X has which is
at X.level, if Y.south_neighbors is not the same as
X.south_neighbors but the nodes share at least one southern
neighbor, for each neighbor N in X.south_neighbors but not in
Y.south_neighbors, add (N, (Y)) to partial_neighbors if N isn't
there or add Y to the list for N.
4. If partial_neighbors is empty, then node X does not disaggregate
any prefixes. If node X is advertising disaggregated prefixes in
its South TIE, X SHOULD remove them and re-advertise its South
TIEs.
A node X computes reachability to all nodes below it based upon the
received North TIEs first. This results in a set of routes, each
categorized by (prefix, path_distance, next-hop set). Alternately,
for clarity in the following procedure, these can be organized by
next-hop set as ((next-hops), {(prefix, path_distance)}). If
partial_neighbors isn't empty, then the procedure in Figure 17
describes how to identify prefixes to disaggregate.
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disaggregated_prefixes = { empty }
nodes_same_level = { empty }
for each South TIE
if (South TIE.level == X.level and
X shares at least one S-neighbor with X)
add South TIE.originator to nodes_same_level
end if
end for
for each next-hop-set NHS
isolated_nodes = nodes_same_level
for each NH in NHS
if NH in partial_neighbors
isolated_nodes =
intersection(isolated_nodes,
partial_neighbors[NH].nodes)
end if
end for
if isolated_nodes is not empty
for each prefix using NHS
add (prefix, distance) to disaggregated_prefixes
end for
end if
end for
copy disaggregated_prefixes to X's South TIE
if X's South TIE is different
schedule South TIE for flooding
end if
Figure 17: Computation of Disaggregated Prefixes
Each disaggregated prefix is sent with the corresponding
path_distance. This allows a node to send the same South TIE to each
south neighbor. The south neighbor which is connected to that prefix
will thus have a shorter path.
Finally, to summarize the less obvious points partially omitted in
the algorithms to keep them more tractable:
1. all neighbor relationships MUST perform backlink checks.
2. overload flag as introduced in Section 6.8.2 and carried in the
_overload_ schema element have to be respected during the
computation. Nodes advertising themselves as overloaded MUST NOT
be transited in reachability computation but MUST be used as
terminal nodes with prefixes they advertise being reachable.
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3. all the lower-level nodes are flooded the same disaggregated
prefixes since RIFT does not build a South TIE per node which
would complicate things unnecessarily. The lower-level node that
can compute a southbound route to the prefix will prefer it to
the disaggregated route anyway based on route preference rules.
4. positively disaggregated prefixes do *not* have to propagate to
lower levels. With that the disturbance in terms of new flooding
is contained to a single level experiencing failures.
5. disaggregated Prefix South TIEs are not "reflected" by the lower
level. Nodes within same level do *not* need to be aware which
node computed the need for disaggregation.
6. The fabric is still supporting maximum load balancing properties
while not trying to send traffic northbound unless necessary.
In case positive disaggregation is triggered and due to the very
stable but un-synchronized nature of the algorithm the nodes may
issue the necessary disaggregated prefixes at different points in
time. This can lead for a short time to an "incast" behavior where
the first advertising router based on the nature of longest prefix
match will attract all the traffic. Different implementation
strategies can be used to lessen that effect, but those are outside
the scope of this specification.
It is worth observing that, in a single plane ToF, this
disaggregation prevents traffic loss up to (K_LEAF * P) link failures
in terms of Section 5.2 or, in other terms, it takes at minimum that
many link failures to partition the ToF into multiple planes.
6.5.2. Negative, Transitive Disaggregation for Fallen Leaves
As explained in Section 5.3 failures in multi-plane ToF or more than
(K_LEAF * P) links failing in single plane design can generate fallen
leaves. Such scenario cannot be addressed by positive disaggregation
only and needs a further mechanism.
6.5.2.1. Cabling of Multiple ToF Planes
Returning in this section to designs with multiple planes as shown
originally in Figure 3, Figure 18 highlights how the ToF is cabled in
case of two planes by the means of dual-rings to distribute all the
North TIEs within both planes.
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____________________________________________________________________________
| [Plane A] . [Plane B] . [Plane C] . [Plane D] |
|..........................................................................|
| +-------------------------------------------------------------+ |
| | +---+ . +---+ . +---+ . +---+ | |
| +-+ n +-------------+ n +-------------+ n +-------------+ n +-+ |
| +--++ . +-+++ . +-+++ . +--++ |
| || . || . || . || |
| +---------||---------------||----------------||---------------+ || |
| | +---+ || . +---+ || . +---+ || . +---+ | || |
| +-+ 1 +---||--------+ 1 +--||---------+ 1 +--||---------+ 1 +-+ || |
| +--++ || . +-+++ || . +-+++ || . +-+++ || |
| || || . || || . || || . || || |
| || || . || || . || || . || || |
Figure 18: Topologically Connected Planes
Section 5.3 already describes how failures in multi-plane fabrics can
lead to traffic loss that normal positive disaggregation cannot fix.
The mechanism of negative, transitive disaggregation incorporated in
RIFT provides the corresponding solution and next section explains
the involved mechanisms in more detail.
6.5.2.2. Transitive Advertisement of Negative Disaggregates
A ToF node discovering that it cannot reach a fallen leaf SHOULD
disaggregate all the prefixes of that leaf. It uses for that purpose
negative prefix South TIEs that are, as usual, flooded southwards
with the scope defined in Section 6.3.4.
Transitively, a node explicitly loses connectivity to a prefix when
none of its children advertises it and when the prefix is negatively
disaggregated by all of its parents. When that happens, the node
originates the negative prefix further down south. Since the
mechanism applies recursively south the negative prefix may propagate
transitively all the way down to the leaf. This is necessary since
leaves connected to multiple planes by means of disjointed paths may
have to choose the correct plane at the very bottom of the fabric to
make sure that they don't send traffic towards another leaf using a
plane where it is "fallen" which would make traffic loss unavoidable.
When connectivity is restored, a node that disaggregated a prefix
withdraws the negative disaggregation by the usual mechanism of re-
advertising TIEs omitting the negative prefix.
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6.5.2.3. Computation of Negative Disaggregates
Negative prefixes can in fact be advertised due to two different
triggers. This will be described consecutively.
The first origination reason is a computation that uses all the node
North TIEs to build the set of all reachable nodes by reachability
computation over the complete graph and including horizontal ToF
links. The computation uses the node itself as root. This is
compared with the result of the normal southbound SPF as described in
Section 6.4.2. The difference are the fallen leaves and all their
attached prefixes are advertised as negative prefixes southbound if
the node does not consider the prefix to be reachable within the
southbound SPF.
The second origination reason hinges on the understanding how the
negative prefixes are used within the computation as described in
Figure 19. When attaching the negative prefixes at a certain point
in time the negative prefix may find itself with all the viable nodes
from the shorter match nexthop being pruned. In other words, all its
northbound neighbors provided a negative prefix advertisement. This
is the trigger to advertise this negative prefix transitively south
and is normally caused by the node being in a plane where the prefix
belongs to a fabric leaf that has "fallen" in this plane. Obviously,
when one of the northbound switches withdraws its negative
advertisement, the node has to withdraw its transitively provided
negative prefix as well.
6.6. Attaching Prefixes
After an SPF is run, it is necessary to attach the resulting
reachability information in form of prefixes. For S-SPF, prefixes
from a North TIE are attached to the originating node with that
node's next-hop set and a distance equal to the prefix's cost plus
the node's minimized path distance. The RIFT route database, a set
of (prefix, prefix-type, attributes, path_distance, next-hop set),
accumulates these results.
N-SPF prefixes from each South TIE need to also be added to the RIFT
route database. The N-SPF is really just a stub so the computing
node needs simply to determine, for each prefix in an South TIE that
originated from adjacent node, what next-hops to use to reach that
node. Since there may be parallel links, the next-hops to use can be
a set; presence of the computing node in the associated Node South
TIE is sufficient to verify that at least one link has bidirectional
connectivity. The set of minimum cost next-hops from the computing
node X to the originating adjacent node is determined.
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Each prefix has its cost adjusted before being added into the RIFT
route database. The cost of the prefix is set to the cost received
plus the cost of the minimum distance next-hop to that neighbor while
considering its attributes such as mobility per Section 6.8.4. Then
each prefix can be added into the RIFT route database with the next-
hop set; ties are broken based upon type first and then distance and
further on _PrefixAttributes_. Only the best combination is used for
forwarding. RIFT route preferences are normalized by the enum
_RouteType_ in Thrift [thrift] model given in Appendix B.
An example implementation for node X follows:
for each South TIE
if South TIE.level > X.level
next_hop_set = set of minimum cost links to the
South TIE.originator
next_hop_cost = minimum cost link to
South TIE.originator
end if
for each prefix P in the South TIE
P.cost = P.cost + next_hop_cost
if P not in route_database:
add (P, P.cost, P.type,
P.attributes, next_hop_set) to route_database
end if
if (P in route_database):
if route_database[P].cost > P.cost or
route_database[P].type > P.type:
update route_database[P] with (P, P.type, P.cost,
P.attributes,
next_hop_set)
else if route_database[P].cost == P.cost and
route_database[P].type == P.type:
update route_database[P] with (P, P.type,
P.cost, P.attributes,
merge(next_hop_set, route_database[P].next_hop_set))
else
// Not preferred route so ignore
end if
end if
end for
end for
Figure 19: Adding Routes from South TIE Positive and Negative
Prefixes
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After the positive prefixes are attached and tie-broken, negative
prefixes are attached and used in case of northbound computation,
ideally from the shortest length to the longest. The nexthop
adjacencies for a negative prefix are inherited from the longest
positive prefix that aggregates it, and subsequently adjacencies to
nodes that advertised negative for this prefix are removed.
The rule of inheritance MUST be maintained when the nexthop list for
a prefix is modified, as the modification may affect the entries for
matching negative prefixes of immediate longer prefix length. For
instance, if a nexthop is added, then by inheritance it must be added
to all the negative routes of immediate longer prefixes length unless
it is pruned due to a negative advertisement for the same next hop.
Similarly, if a nexthop is deleted for a given prefix, then it is
deleted for all the immediately aggregated negative routes. This
will recurse in the case of nested negative prefix aggregations.
The rule of inheritance MUST also be maintained when a new prefix of
intermediate length is inserted, or when the immediately aggregating
prefix is deleted from the routing table, making an even shorter
aggregating prefix the one from which the negative routes now inherit
their adjacencies. As the aggregating prefix changes, all the
negative routes MUST be recomputed, and then again the process may
recurse in case of nested negative prefix aggregations.
Although these operations can be computationally expensive, the
overall load on devices in the network is low because these
computations are not run very often, as positive route advertisements
are always preferred over negative ones. This prevents recursion in
most cases because positive reachability information never inherits
next hops.
To make the negative disaggregation less abstract and provide an
example ToP node T1 with 4 ToF parents S1..S4 as represented in
Figure 20 are considered further:
+----+ +----+ +----+ +----+ N
| S1 | | S2 | | S3 | | S4 | ^
+----+ +----+ +----+ +----+ W< + >E
| | | | v
|+--------+ | | S
||+-----------------+ |
|||+----------------+---------+
||||
+----+
| T1 |
+----+
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Figure 20: A ToP Node with 4 Parents
If all ToF nodes can reach all the prefixes in the network; with
RIFT, they will normally advertise a default route south. An
abstract Routing Information Base (RIB), more commonly known as a
routing table, stores all types of maintained routes including the
negative ones and "tie-breaks" for the best one, whereas an abstract
Forwarding table (FIB) retains only the ultimately computed
"positive" routing instructions. In T1, those tables would look as
illustrated in Figure 21:
+---------+
| Default |
+---------+
|
| +--------+
+---> | Via S1 |
| +--------+
|
| +--------+
+---> | Via S2 |
| +--------+
|
| +--------+
+---> | Via S3 |
| +--------+
|
| +--------+
+---> | Via S4 |
+--------+
Figure 21: Abstract RIB
In case T1 receives a negative advertisement for prefix 2001:db8::/32
from S1 a negative route is stored in the RIB (indicated by a ~
sign), while the more specific routes to the complementing ToF nodes
are installed in FIB. RIB and FIB in T1 now look as illustrated in
Figure 22 and Figure 23, respectively:
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+---------+ +-----------------+
| Default | <-------------- | ~2001:db8::/32 |
+---------+ +-----------------+
| |
| +--------+ | +--------+
+---> | Via S1 | +---> | Via S1 |
| +--------+ +--------+
|
| +--------+
+---> | Via S2 |
| +--------+
|
| +--------+
+---> | Via S3 |
| +--------+
|
| +--------+
+---> | Via S4 |
+--------+
Figure 22: Abstract RIB after Negative 2001:db8::/32 from S1
The negative 2001:db8::/32 prefix entry inherits from ::/0, so the
positive more specific routes are the complements to S1 in the set of
next-hops for the default route. That entry is composed of S2, S3,
and S4, or, in other words, it uses all entries in the default route
with a "hole punched" for S1 into them. These are the next hops that
are still available to reach 2001:db8::/32, now that S1 advertised
that it will not forward 2001:db8::/32 anymore. Ultimately, those
resulting next-hops are installed in FIB for the more specific route
to 2001:db8::/32 as illustrated below:
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+---------+ +---------------+
| Default | | 2001:db8::/32 |
+---------+ +---------------+
| |
| +--------+ |
+---> | Via S1 | |
| +--------+ |
| |
| +--------+ | +--------+
+---> | Via S2 | +---> | Via S2 |
| +--------+ | +--------+
| |
| +--------+ | +--------+
+---> | Via S3 | +---> | Via S3 |
| +--------+ | +--------+
| |
| +--------+ | +--------+
+---> | Via S4 | +---> | Via S4 |
+--------+ +--------+
Figure 23: Abstract FIB after Negative 2001:db8::/32 from S1
To illustrate matters further consider T1 receiving a negative
advertisement for prefix 2001:db8:1::/48 from S2, which is stored in
RIB again. After the update, the RIB in T1 is illustrated in
Figure 24:
+---------+ +----------------+ +------------------+
| Default | <----- | ~2001:db8::/32 | <------ | ~2001:db8:1::/48 |
+---------+ +----------------+ +------------------+
| | |
| +--------+ | +--------+ |
+---> | Via S1 | +---> | Via S1 | |
| +--------+ +--------+ |
| |
| +--------+ | +--------+
+---> | Via S2 | +---> | Via S2 |
| +--------+ +--------+
|
| +--------+
+---> | Via S3 |
| +--------+
|
| +--------+
+---> | Via S4 |
+--------+
Figure 24: Abstract RIB after Negative 2001:db8:1::/48 from S2
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Negative 2001:db8:1::/48 inherits from 2001:db8::/32 now, so the
positive more specific routes are the complements to S2 in the set of
next hops for 2001:db8::/32, which are S3 and S4, or, in other words,
all entries of the parent with the negative holes "punched in" again.
After the update, the FIB in T1 shows as illustrated in Figure 25:
+---------+ +---------------+ +-----------------+
| Default | | 2001:db8::/32 | | 2001:db8:1::/48 |
+---------+ +---------------+ +-----------------+
| | |
| +--------+ | |
+---> | Via S1 | | |
| +--------+ | |
| | |
| +--------+ | +--------+ |
+---> | Via S2 | +---> | Via S2 | |
| +--------+ | +--------+ |
| | |
| +--------+ | +--------+ | +--------+
+---> | Via S3 | +---> | Via S3 | +---> | Via S3 |
| +--------+ | +--------+ | +--------+
| | |
| +--------+ | +--------+ | +--------+
+---> | Via S4 | +---> | Via S4 | +---> | Via S4 |
+--------+ +--------+ +--------+
Figure 25: Abstract FIB after Negative 2001:db8:1::/48 from S2
Further, assume that S3 stops advertising its service as default
gateway. The entry is removed from RIB as usual. In order to update
the FIB, it is necessary to eliminate the FIB entry for the default
route, as well as all the FIB entries that were created for negative
routes pointing to the RIB entry being removed (::/0). This is done
recursively for 2001:db8::/32 and then for, 2001:db8:1::/48. The
related FIB entries via S3 are removed, as illustrated in Figure 26.
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+---------+ +---------------+ +-----------------+
| Default | | 2001:db8::/32 | | 2001:db8:1::/48 |
+---------+ +---------------+ +-----------------+
| | |
| +--------+ | |
+---> | Via S1 | | |
| +--------+ | |
| | |
| +--------+ | +--------+ |
+---> | Via S2 | +---> | Via S2 | |
| +--------+ | +--------+ |
| | |
| | |
| | |
| | |
| | |
| +--------+ | +--------+ | +--------+
+---> | Via S4 | +---> | Via S4 | +---> | Via S4 |
+--------+ +--------+ +--------+
Figure 26: Abstract FIB after Loss of S3
Say that at that time, S4 would also disaggregate prefix
2001:db8:1::/48. This would mean that the FIB entry for
2001:db8:1::/48 becomes a discard route, and that would be the signal
for T1 to disaggregate prefix 2001:db8:1::/48 negatively in a
transitive fashion with its own children.
Finally, the case occurs where S3 becomes available again as a
default gateway, and a negative advertisement is received from S4
about prefix 2001:db8:2::/48 as opposed to 2001:db8:1::/48. Again, a
negative route is stored in the RIB, and the more specific route to
the complementing ToF nodes are installed in FIB. Since
2001:db8:2::/48 inherits from 2001:db8::/32, the positive FIB routes
are chosen by removing S4 from S2, S3, S4. The abstract FIB in T1
now shows as illustrated in Figure 27:
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+-----------------+
| 2001:db8:2::/48 |
+-----------------+
|
+---------+ +---------------+ +-----------------+
| Default | | 2001:db8::/32 | | 2001:db8:1::/48 |
+---------+ +---------------+ +-----------------+
| | | |
| +--------+ | | | +--------+
+---> | Via S1 | | | +---> | Via S2 |
| +--------+ | | | +--------+
| | | |
| +--------+ | +--------+ | | +--------+
+---> | Via S2 | +---> | Via S2 | | +---> | Via S3 |
| +--------+ | +--------+ | +--------+
| | |
| +--------+ | +--------+ | +--------+
+---> | Via S3 | +---> | Via S3 | +---> | Via S3 |
| +--------+ | +--------+ | +--------+
| | |
| +--------+ | +--------+ | +--------+
+---> | Via S4 | +---> | Via S4 | +---> | Via S4 |
+--------+ +--------+ +--------+
Figure 27: Abstract FIB after Negative 2001:db8:2::/48 from S4
6.7. Optional Zero Touch Provisioning (ZTP)
Each RIFT node can operate in zero touch provisioning (ZTP) mode,
i.e. it has no configuration (unless it is a ToF or it is explicitly
configured to operate in the overall topology as leaf and/or support
leaf-2-leaf procedures) and it will fully configure itself after
being attached to the topology. Configured nodes and nodes operating
in ZTP can be mixed and will form a valid topology if achievable.
The derivation of the level of each node happens based on offers
received from its neighbors whereas each node (with possibly
exceptions of configured leaves) tries to attach at the highest
possible point in the fabric. This guarantees that even if the
diffusion front of offers reaches a node from "below" faster than
from "above", it will greedily abandon already negotiated level
derived from nodes topologically below it and properly peer with
nodes above.
The fabric is very consciously numbered from the top down to allow
for PoDs of different heights and minimize the number of
provisionings necessary, in this case just a TOP_OF_FABRIC flag on
every node at the top of the fabric.
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This section describes the necessary concepts and procedures for ZTP
operation.
6.7.1. Terminology
The interdependencies between the different flags and the configured
level can be somewhat vexing at first and it may take multiple reads
of the glossary to comprehend them.
Automatic Level Derivation:
Procedures which allow nodes without level configured to derive it
automatically. Only applied if CONFIGURED_LEVEL is undefined.
UNDEFINED_LEVEL:
A "null" value that indicates that the level has not been
determined and has not been configured. Schemas normally indicate
that by a missing optional value without an available defined
default.
LEAF_ONLY:
An optional configuration flag that can be configured on a node to
make sure it never leaves the "bottom of the hierarchy".
TOP_OF_FABRIC flag and CONFIGURED_LEVEL cannot be defined at the
same time as this flag. It implies CONFIGURED_LEVEL value of
_leaf_level_. It is indicated in the _leaf_only_ schema element.
TOP_OF_FABRIC:
A configuration flag that MUST be provided on all ToF nodes.
LEAF_FLAG and CONFIGURED_LEVEL cannot be defined at the same time
as this flag. It implies a CONFIGURED_LEVEL value. In fact, it
is basically a shortcut for configuring same level at all ToF
nodes which is unavoidable since an initial 'seed' is needed for
other ZTP nodes to derive their level in the topology. The flag
plays an important role in fabrics with multiple planes to enable
successful negative disaggregation (Section 6.5.2). It is carried
in the _top_of_fabric_ schema element. A standards conform RIFT
implementation implies a CONFIGURED_LEVEL value of
_top_of_fabric_level_ in case of TOP_OF_FABRIC. This value is
kept reasonably low to allow for fast ZTP re-convergence on
failures.
CONFIGURED_LEVEL:
A level value provided manually. When this is defined (i.e. it is
not an UNDEFINED_LEVEL) the node is not participating in ZTP in
the sense of deriving its own level based on other nodes'
information. TOP_OF_FABRIC flag is ignored when this value is
defined. LEAF_ONLY can be set only if this value is undefined or
set to _leaf_level_.
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DERIVED_LEVEL:
Level value computed via automatic level derivation when
CONFIGURED_LEVEL is equal to UNDEFINED_LEVEL.
LEAF_2_LEAF:
An optional flag that can be configured on a node to make sure it
supports procedures defined in Section 6.8.9. It is a capability
that implies LEAF_ONLY and the corresponding restrictions.
TOP_OF_FABRIC flag is ignored when set at the same time as this
flag. It is carried in the _leaf_only_and_leaf_2_leaf_procedures_
schema flag.
LEVEL_VALUE:
With ZTP, the original definition of "level" in Section 3.1 is
both extended and relaxed. First, level is defined now as
LEVEL_VALUE and is the first defined value of CONFIGURED_LEVEL
followed by DERIVED_LEVEL. Second, it is possible for nodes to be
more than one level apart to form adjacencies if any of the nodes
is at least LEAF_ONLY.
Valid Offered Level (VOL):
A neighbor's level received in a valid LIE (i.e. passing all
checks for adjacency formation while disregarding all clauses
involving level values) persisting for the duration of the
holdtime interval on the LIE. Observe that offers from nodes
offering level value of _leaf_level_ do not constitute VOLs (since
no valid DERIVED_LEVEL can be obtained from those and consequently
_not_a_ztp_offer_ flag MUST be ignored). Offers from LIEs with
_not_a_ztp_offer_ being true are not VOLs either. If a node
maintains parallel adjacencies to the neighbor, VOL on each
adjacency is considered as equivalent, i.e. the newest VOL from
any such adjacency updates the VOL received from the same node.
Highest Available Level (HAL):
Highest defined level value received from all VOLs received.
Highest Available Level Systems (HALS):
Set of nodes offering HAL VOLs.
Highest Adjacency ThreeWay (HAT):
Highest neighbor level of all the formed _ThreeWay_ adjacencies
for the node.
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6.7.2. Automatic System ID Selection
RIFT nodes require a 64-bit System ID which SHOULD be derived as
EUI-64 MA-L derive according to [EUI64]. The organizationally
governed portion of this ID (24 bits) can be used to generate
multiple IDs if required to indicate more than one RIFT instance.
As matter of operational concern, the router MUST ensure that such
identifier is not changing very frequently (or at least not without
sending all its TIEs with fairly short lifetimes, i.e. purging them)
since otherwise the network may be left with large amounts of stale
TIEs in other nodes (though this is not necessarily a serious problem
if the procedures described in Section 9 are implemented).
6.7.3. Generic Fabric Example
ZTP forces considerations of an incorrectly or unusually cabled
fabric and how such a topology can be forced into a "lattice"
structure which a fabric represents (with further restrictions). A
necessary and sufficient physical cabling is shown in Figure 28. The
assumption here is that all nodes are in the same PoD.
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+---+
| A | s = TOP_OF_FABRIC
| s | l = LEAF_ONLY
++-++ l2l = LEAF_2_LEAF
| |
+--+ +--+
| |
+--++ ++--+
| E | | F |
| +-+ | +-----------+
++--+ | ++-++ |
| | | | |
| +-------+ | |
| | | | |
| | +----+ | |
| | | | |
++-++ ++-++ |
| I +-----+ J | |
| | | +-+ |
++-++ +--++ | |
| | | | |
+---------+ | +------+ |
| | | | |
+-----------------+ | |
| | | | |
++-++ ++-++ |
| X +-----+ Y +-+
|l2l| | l |
+---+ +---+
Figure 28: Generic ZTP Cabling Considerations
First, RIFT must anchor the "top" of the cabling and that's what the
TOP_OF_FABRIC flag at node A is for. Then things look smooth until
the protocol has to decide whether node Y is at the same level as I,
J (and as consequence, X is south of it) or at the same level as X.
This is unresolvable here until we "nail down the bottom" of the
topology. To achieve that the protocol chooses to use in this
example the leaf flags in X and Y. In case where Y would not have a
leaf flag it will try to elect highest level offered and end up being
in same level as I and J.
6.7.4. Level Determination Procedure
A node starting up with UNDEFINED_VALUE (i.e. without a
CONFIGURED_LEVEL or any leaf or TOP_OF_FABRIC flag) MUST follow those
additional procedures:
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1. It advertises its LEVEL_VALUE on all LIEs (observe that this can
be UNDEFINED_LEVEL which in terms of the schema is simply an
omitted optional value).
2. It computes HAL as numerically highest available level in all
VOLs.
3. It chooses then MAX(HAL-1,0) as its DERIVED_LEVEL. The node then
starts to advertise this derived level.
4. A node that lost all adjacencies with HAL value MUST hold down
computation of new DERIVED_LEVEL for at least one second unless
it has no VOLs from southbound adjacencies. After the holddown
timer expired, it MUST discard all received offers, recompute
DERIVED_LEVEL and announce it to all neighbors.
5. A node MUST reset any adjacency that has changed the level it is
offering and is in _ThreeWay_ state.
6. A node that changed its defined level value MUST readvertise its
own TIEs (since the new _PacketHeader_ will contain a different
level than before). The sequence number of each TIE MUST be
increased.
7. After a level has been derived the node MUST set the
_not_a_ztp_offer_ on LIEs towards all systems offering a VOL for
HAL.
8. A node that changed its level SHOULD flush from its link state
database TIEs of all other nodes, otherwise stale information may
persist on "direction reversal", i.e., nodes that seemed south
are now north or east-west. This will not prevent the correct
operation of the protocol but could be slightly confusing
operationally.
A node starting with LEVEL_VALUE being 0 (i.e., it assumes a leaf
function by being configured with the appropriate flags or has a
CONFIGURED_LEVEL of 0) MUST follow those additional procedures:
1. It computes HAT per procedures above but does *not* use it to
compute DERIVED_LEVEL. HAT is used to limit adjacency formation
per Section 6.2.
It MAY also follow modified procedures:
1. It may pick a different strategy to choose VOL, e.g. use the VOL
value with highest number of VOLs. Such strategies are only
possible since the node always remains "at the bottom of the
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fabric" while another layer could "invert" the fabric by picking
its preferred VOL in a different fashion than always trying to
achieve the highest viable level.
6.7.5. ZTP FSM
This section specifies the precise, normative ZTP FSM and can be
omitted unless the reader is pursuing an implementation of the
protocol. For additional clarity a graphical representation of the
ZTP FSM is depicted in Figure 29. It may also be helpful to refer to
the normative schema in Appendix B.
Initial state is ComputeBestOffer.
Enter
|
v
+------------------+
| ComputeBestOffer |
| |<----+
| | | BetterHAL
| | | BetterHAT
| | | ChangeLocalConfiguredLevel
| | | ChangeLocalHierarchyIndications
| | | LostHAT
| | | NeighborOffer
| | | ShortTic
| |-----+
| |
| |<---------------------
| |---------------------> (UpdatingClients)
| | ComputationDone
+------------------+
^ |
| | LostHAL
| V
(HoldingDown)
(ComputeBestOffer)
| ^
| | ChangeLocalConfiguredLevel
| | ChangeLocalHierarchyIndications
| | HoldDownExpired
V |
+------------------+
| HoldingDown |
| |<----+
| | | BetterHAL
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| | | BetterHAT
| | | ComputationDone
| | | LostHAL
| | | LostHat
| | | NeighborOffer
| | | ShortTic
| |-----+
+------------------+
^
|
(UpdatingClients)
(ComputeBestOffer)
| ^
| | BetterHAL
| | BetterHAT
| | LostHAT
| | ChangeLocalHierarchyIndications
| | ChangeLocalConfiguredLevel
V |
+------------------+
| UpdatingClients |
| |<----+
| | |
| | | NeighborOffer
| | | ShortTic
| |-----+
+------------------+
|
| LostHAL
V
(HoldingDown)
Figure 29: ZTP FSM
The following words are used for well-known procedures:
* PUSH Event: queues an event to be executed by the FSM upon exit of
this action
* COMPARE_OFFERS: checks whether based on current offers and held
last results, the events BetterHAL/LostHAL/BetterHAT/LostHAT are
necessary and returns them
* UPDATE_OFFER: store current offer with adjacency holdtime as
lifetime and COMPARE_OFFERS, then PUSH corresponding events
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* LEVEL_COMPUTE: compute best offered or configured level and HAL/
HAT, if anything changed PUSH ComputationDone
* REMOVE_OFFER: remove the corresponding offer and COMPARE_OFFERS,
PUSH corresponding events
* PURGE_OFFERS: REMOVE_OFFER for all held offers, COMPARE OFFERS,
PUSH corresponding events
* PROCESS_OFFER:
1. if no level offered then REMOVE_OFFER
2. else
1. if offered level > leaf then UPDATE_OFFER
2. else REMOVE_OFFER
States:
* ComputeBestOffer: processes received offers to derive ZTP
variables
* HoldingDown: holding down while receiving updates
* UpdatingClients: updates other FSMs on the same node with
computation results
Events:
* ChangeLocalHierarchyIndications: node locally configured with new
leaf flags.
* ChangeLocalConfiguredLevel: node locally configured with a defined
level
* NeighborOffer: a new neighbor offer with optional level and
neighbor state.
* BetterHAL: better HAL computed internally.
* BetterHAT: better HAT computed internally.
* LostHAL: lost last HAL in computation.
* LostHAT: lost HAT in computation.
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* ComputationDone: computation performed.
* HoldDownExpired: holddown timer expired.
* ShortTic: one second timer tick. This event is provided to the
FSM once a second by an implementation-specific mechanism that is
outside the scope of this specification. This event is quietly
ignored if the relevant transition does not exist.
Actions:
* on ChangeLocalConfiguredLevel in HoldingDown finishes in
ComputeBestOffer: store configured level
* on BetterHAT in HoldingDown finishes in HoldingDown: no action
* on ShortTic in HoldingDown finishes in HoldingDown: remove expired
offers and if holddown timer expired PUSH_EVENT HoldDownExpired
* on NeighborOffer in HoldingDown finishes in HoldingDown:
PROCESS_OFFER
* on ComputationDone in HoldingDown finishes in HoldingDown: no
action
* on BetterHAL in HoldingDown finishes in HoldingDown: no action
* on LostHAT in HoldingDown finishes in HoldingDown: no action
* on LostHAL in HoldingDown finishes in HoldingDown: no action
* on HoldDownExpired in HoldingDown finishes in ComputeBestOffer:
PURGE_OFFERS
* on ChangeLocalHierarchyIndications in HoldingDown finishes in
ComputeBestOffer: store leaf flags
* on LostHAT in ComputeBestOffer finishes in ComputeBestOffer:
LEVEL_COMPUTE
* on NeighborOffer in ComputeBestOffer finishes in ComputeBestOffer:
PROCESS_OFFER
* on BetterHAT in ComputeBestOffer finishes in ComputeBestOffer:
LEVEL_COMPUTE
* on ChangeLocalHierarchyIndications in ComputeBestOffer finishes in
ComputeBestOffer: store leaf flags and LEVEL_COMPUTE
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* on LostHAL in ComputeBestOffer finishes in HoldingDown: if any
southbound adjacencies present then update holddown timer to
normal duration else fire holddown timer immediately
* on ShortTic in ComputeBestOffer finishes in ComputeBestOffer:
remove expired offers
* on ComputationDone in ComputeBestOffer finishes in
UpdatingClients: no action
* on ChangeLocalConfiguredLevel in ComputeBestOffer finishes in
ComputeBestOffer: store configured level and LEVEL_COMPUTE
* on BetterHAL in ComputeBestOffer finishes in ComputeBestOffer:
LEVEL_COMPUTE
* on ShortTic in UpdatingClients finishes in UpdatingClients: remove
expired offers
* on LostHAL in UpdatingClients finishes in HoldingDown: if any
southbound adjacencies are present then update holddown timer to
normal duration else fire holddown timer immediately
* on BetterHAT in UpdatingClients finishes in ComputeBestOffer: no
action
* on BetterHAL in UpdatingClients finishes in ComputeBestOffer: no
action
* on ChangeLocalConfiguredLevel in UpdatingClients finishes in
ComputeBestOffer: store configured level
* on ChangeLocalHierarchyIndications in UpdatingClients finishes in
ComputeBestOffer: store leaf flags
* on NeighborOffer in UpdatingClients finishes in UpdatingClients:
PROCESS_OFFER
* on LostHAT in UpdatingClients finishes in ComputeBestOffer: no
action
* on Entry into ComputeBestOffer: LEVEL_COMPUTE
* on Entry into UpdatingClients: update all LIE FSMs with
computation results
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6.7.6. Resulting Topologies
The procedures defined in Section 6.7.4 will lead to the RIFT
topology and levels depicted in Figure 30.
+---+
| As|
| 24|
++-++
| |
+--+ +--+
| |
+--++ ++--+
| E | | F |
| 23+-+ | 23+-----------+
++--+ | ++-++ |
| | | | |
| +-------+ | |
| | | | |
| | +----+ | |
| | | | |
++-++ ++-++ |
| I +-----+ J | |
| 22| | 22| |
++--+ +--++ |
| | |
+---------+ | |
| | |
++-++ +---+ |
| X | | Y +-+
| 0 | | 0 |
+---+ +---+
Figure 30: Generic ZTP Topology Autoconfigured
In case where the LEAF_ONLY restriction on Y is removed the outcome
would be very different however and result in Figure 31. This
demonstrates basically that auto configuration makes miscabling
detection hard and with that can lead to undesirable effects in cases
where leaves are not "nailed" by the appropriately configured flags
and arbitrarily cabled.
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+---+
| As|
| 24|
++-++
| |
+--+ +--+
| |
+--++ ++--+
| E | | F |
| 23+-+ | 23+-------+
++--+ | ++-++ |
| | | | |
| +-------+ | |
| | | | |
| | +----+ | |
| | | | |
++-++ ++-++ +-+-+
| I +-----+ J +-----+ Y |
| 22| | 22| | 22|
++-++ +--++ ++-++
| | | | |
| +-----------------+ |
| | |
+---------+ | |
| | |
++-++ |
| X +--------+
| 0 |
+---+
Figure 31: Generic ZTP Topology Autoconfigured
6.8. Further Mechanisms
6.8.1. Route Preferences
Since RIFT distinguishes between different route types such as e.g.
external routes from other protocols and additionally advertises
special types of routes on disaggregation, the protocol MUST tie-
break internally different types on a clear preference scale to
prevent traffic loss or loops. The preferences are given in the
schema type _RouteType_.
Table Table 5 contains the route type as derived from the TIE type
carrying it. Entries are sorted from the most preferred route type
to the least preferred route type.
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+==================================+======================+
| TIE Type | Resulting Route Type |
+==================================+======================+
| None | Discard |
+----------------------------------+----------------------+
| Local Interface | LocalPrefix |
+----------------------------------+----------------------+
| S-PGP | South PGP |
+----------------------------------+----------------------+
| N-PGP | North PGP |
+----------------------------------+----------------------+
| North Prefix | NorthPrefix |
+----------------------------------+----------------------+
| North External Prefix | NorthExternalPrefix |
+----------------------------------+----------------------+
| South Prefix and South Positive | SouthPrefix |
| Disaggregation | |
+----------------------------------+----------------------+
| South External Prefix and South | SouthExternalPrefix |
| Positive External Disaggregation | |
+----------------------------------+----------------------+
| South Negative Prefix | NegativeSouthPrefix |
+----------------------------------+----------------------+
Table 5: TIEs and Contained Route Types
6.8.2. Overload Bit
Overload attribute is specified in the packet encoding schema
(Appendix B) in the _overload_ flag.
The overload flag MUST be respected by all necessary SPF
computations. A node with the overload flag set SHOULD advertise all
locally hosted prefixes both northbound and southbound, all other
southbound prefixes SHOULD NOT be advertised.
Leaf nodes SHOULD set the overload attribute on all originated Node
TIEs. If spine nodes were to forward traffic not intended for the
local node, the leaf node would not be able to prevent routing/
forwarding loops as it does not have the necessary topology
information to do so.
6.8.3. Optimized Route Computation on Leaves
Leaf nodes only have visibility to directly connected nodes and
therefore are not required to run "full" SPF computations. Instead,
prefixes from neighboring nodes can be gathered to run a "partial"
SPF computation in order to build the routing table.
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Leaf nodes SHOULD only hold their own N-TIEs, and in cases of L2L
implementations, the N-TIEs of their East/West neighbors. Leaf nodes
MUST hold all S-TIEs from their neighbors.
Normally, a full network graph is created based on local N-TIEs and
remote S-TIEs that it receives from neighbors, at which time,
necessary SPF computations are performed. Instead, leaf nodes can
simply compute the minimum cost and next-hop set of each leaf
neighbor by examining its local adjacencies. Associated N-TIEs are
used to determine bi-directionality and derive the next-hop set.
Cost is then derived from the minimum cost of the local adjacency to
the neighbor and the prefix cost.
Leaf nodes would then attach necessary prefixes as described in
Section 6.6.
6.8.4. Mobility
The RIFT control plane MUST maintain the real time status of every
prefix, to which port it is attached, and to which leaf node that
port belongs. This is still true in cases of IP mobility where the
point of attachment may change several times a second.
There are two classic approaches to explicitly maintain this
information, "timestamp" and "sequence counter" as follows:
timestamp:
With this method, the infrastructure SHOULD record the precise
time at which the movement is observed. One key advantage of this
technique is that it has no dependency on the mobile device. One
drawback is that the infrastructure MUST be precisely synchronized
in order to be able to compare timestamps as the points of
attachment change. This could be accomplished by utilizing
Precision Time Protocol (PTP) IEEE Std. 1588 [IEEEstd1588] or
802.1AS [IEEEstd8021AS] which is designed for bridged LANs. Both
the precision of the synchronization protocol and the resolution
of the timestamp must beat the shortest possible roaming time on
the fabric. Another drawback is that the presence of a mobile
device may only be observed asynchronously, such as when it starts
using an IP protocol like ARP [RFC0826], IPv6 Neighbor Discovery
[RFC4861], IPv6 Stateless Address Configuration [RFC4862], DHCP
[RFC2131], or DHCPv6 [RFC8415].
sequence counter:
With this method, a mobile device notifies its point of attachment
on arrival with a sequence counter that is incremented upon each
movement. On the positive side, this method does not have a
dependency on a precise sense of time, since the sequence of
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movements is kept in order by the mobile device. The disadvantage
of this approach is the need for support for protocols that may be
used by the mobile device to register its presence to the leaf
node with the capability to provide a sequence counter. Well-
known issues with sequence counters such as wrapping and
comparison rules MUST be addressed properly. Sequence numbers
MUST be compared by a single homogenous source to make operation
feasible. Sequence number comparison from multiple heterogeneous
sources would be extremely difficult to implement.
RIFT supports a hybrid approach by using an optional
'PrefixSequenceType' attribute (that is also called a
_monotonic_clock_ in the schema) that consists of a timestamp and
optional sequence number field. In case of a negatively distributed
prefix this attribute MUST NOT be included by the originator and it
MUST be ignored by all nodes during computation. When this attribute
is present (observe that per data schema the attribute itself is
optional but in case it is included the 'timestamp' field is
required):
* The leaf node MAY advertise a timestamp of the latest sighting of
a prefix, e.g., by snooping IP protocols or the node using the
time at which it advertised the prefix. RIFT transports the
timestamp within the desired prefix North TIEs as [IEEEstd1588]
timestamp.
* RIFT MAY interoperate with "Registration Extensions for 6LoWPAN
Neighbor Discovery" [RFC8505], which provides a method for
registering a prefix with a sequence number called a Transaction
ID (TID). In such cases, RIFT SHOULD transport the derived TID
without modification.
* RIFT also defines an abstract negative clock (ASNC) (also called
an 'undefined' clock). The ASNC MUST be considered older than any
other defined clock. By default, when a node receives a prefix
North TIE that does not contain a 'PrefixSequenceType' attribute,
it MUST interpret the absence as the ASNC.
* Any prefix present on the fabric in multiple nodes that have the
*same* clock is considered as anycast.
* RIFT specification assumes that all nodes are being synchronized
within at least 200 milliseconds or less. This is achievable
through the use of NTP [RFC5905]. An implementation MAY provide a
way to reconfigure a domain to a different value, and provides for
this purpose a variable called MAXIMUM_CLOCK_DELTA.
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6.8.4.1. Clock Comparison
All monotonic clock values MUST be compared to each other using the
following rules:
1. The ASNC is older than any other value except ASNC *and*
2. Clocks with timestamp differing by more than MAXIMUM_CLOCK_DELTA
are comparable by using the timestamps only *and*
3. Clocks with timestamps differing by less than MAXIMUM_CLOCK_DELTA
are comparable by using their TIDs only *and*
4. An undefined TID is always older than any other TID *and*
5. TIDs are compared using rules of [RFC8505].
6.8.4.2. Interaction between Time Stamps and Sequence Counters
For attachment changes that occur less frequently (e.g., once per
second), the timestamp that the RIFT infrastructure captures should
be enough to determine the most current discovery. If the point of
attachment changes faster than the maximum drift of the time stamping
mechanism (i.e., MAXIMUM_CLOCK_DELTA), then a sequence number SHOULD
be used to enable necessary precision to determine currency.
The sequence counter in [RFC8505] is encoded as one octet and wraps
around using Appendix A.
Within the resolution of MAXIMUM_CLOCK_DELTA, sequence counter values
captured during 2 sequential iterations of the same timestamp SHOULD
be comparable. This means that with default values, a node may move
up to 127 times in a 200 millisecond period and the clocks will
remain comparable. This allows the RIFT infrastructure to explicitly
assert the most up-to-date advertisement.
6.8.4.3. Anycast vs. Unicast
A unicast prefix can be attached to at most one leaf, whereas an
anycast prefix may be reachable via more than one leaf.
If a monotonic clock attribute is provided on the prefix, then the
prefix with the *newest* clock value is strictly preferred. An
anycast prefix does not carry a clock or all clock attributes MUST be
the same under the rules of Section 6.8.4.1.
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It is important that in mobility events the leaf is re-flooding as
quickly as possible to communicate the absence of the prefix that
moved.
Without support for [RFC8505] movements on the fabric within
intervals smaller than 100msec will be interpreted as anycast.
6.8.4.4. Overlays and Signaling
RIFT is agnostic to any overlay technologies and their associated
control and transports that run on top of it (e.g. VXLAN). It is
expected that leaf nodes and possibly ToF nodes can perform necessary
data plane encapsulation.
In the context of mobility, overlays provide another possible
solution to avoid injecting mobile prefixes into the fabric as well
as improving scalability of the deployment. It makes sense to
consider overlays for mobility solutions in IP fabrics. As an
example, a mobility protocol such as LISP [RFC9300] [RFC9301] may
inform the ingress leaf of the location of the egress leaf in real
time.
Another possibility is to consider that mobility as an underlay
service and support it in RIFT to an extent. The load on the fabric
increases with the amount of mobility obviously since a move forces
flooding and computation on all nodes in the scope of the move so
tunneling from leaf to the ToF may be desired to speed up convergence
times.
6.8.5. Key/Value (KV) Store
6.8.5.1. Southbound
RIFT supports the southbound distribution of key-value pairs that can
be used to distribute information to facilitate higher levels of
functionality (e.g. distribution of configuration information). KV
South TIEs may arrive from multiple nodes and therefore MUST execute
the following tie-breaking rules for each key:
1. Only KV TIEs received from nodes to which a bi-directional
adjacency exists MUST be considered.
2. For each valid KV South TIEs that contains the same key, the
value within the South TIE with the highest level will be
preferred. If the levels are identical, the highest originating
System ID will be preferred. In the case of overlapping keys in
the winning South TIE, the behavior is undefined.
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Consider that if a node goes down, nodes south of it will lose
associated adjacencies causing them to disregard corresponding KVs.
New KV South TIEs are advertised to prevent stale information being
used by nodes that are further south. KV advertisements southbound
are not a result of independent computation by every node over the
same set of South TIEs, but a diffused computation.
6.8.5.2. Northbound
Certain use cases necessitate distribution of essential KV
information that is generated by the leaves in the northbound
direction. Such information is flooded in KV North TIEs. Since the
originator of the KV North TIEs is preserved during flooding, the
corresponding mechanism will define, if necessary, tie-breaking rules
depending on the semantics of the information.
Only KV TIEs from nodes that are reachable via multiplane
reachability computation mentioned in Section 6.5.2.3 SHOULD be
considered.
6.8.6. Interactions with BFD
RIFT MAY incorporate BFD [RFC5881] to react quickly to link failures.
In such case, the following procedures are introduced:
After RIFT _ThreeWay_ hello adjacency convergence a BFD session
MAY be formed automatically between the RIFT endpoints without
further configuration using the exchanged discriminators that are
equal to the _local_id_ in the _LIEPacket_. The capability of the
remote side to support BFD is carried in the LIEs in
_LinkCapabilities_.
In case an established BFD session goes Down after it was Up, RIFT
adjacency SHOULD be re-initialized and subsequently started from
Init after it receives a consecutive BFD Up.
In case of parallel links between nodes each link MAY run its own
independent BFD session or they MAY share a session. The specific
manner in which this is implemented is outside the scope of this
document.
If link identifiers or BFD capabilities change, both the LIE and
any BFD sessions SHOULD be brought down and back up again. In
case only the advertised capabilities change, the node MAY choose
to persist the BFD session.
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Multiple RIFT instances MAY choose to share a single BFD session,
in such cases the behavior for which discriminators are used is
undefined. However, RIFT MAY advertise the same link ID for the
same interface in multiple instances to "share" discriminators.
The BFD TTL follows [RFC5082].
6.8.7. Fabric Bandwidth Balancing
A well understood problem in fabrics is that, in case of link
failures, it would be ideal to rebalance how much traffic is sent to
switches in the next level based on available ingress and egress
bandwidth.
RIFT supports a light-weight mechanism that can deal with the problem
based on the fact that RIFT is loop-free.
6.8.7.1. Northbound Direction
Every RIFT node SHOULD compute the amount of northbound bandwidth
available through neighbors at a higher level and modify the distance
received on default route from these neighbors. The bandwidth is
advertised in _NodeNeighborsTIEElement_ element which represents the
sum of the bandwidths of all the parallel links to a neighbor.
Default routes with differing distances SHOULD be used to support
weighted ECMP forwarding. Such a distance is called Bandwidth
Adjusted Distance (BAD). This is best illustrated by a simple
example.
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100 x 100 100 MBits
| x | |
+-+---+-+ +-+---+-+
| | | |
|Spin111| |Spin112|
+-+---+++ ++----+++
|x || || ||
|| |+---------------+ ||
|| +---------------+| ||
|| || || ||
|| || || ||
-----All Links 10 MBit-------
|| || || ||
|| || || ||
|| +------------+| || ||
|| |+------------+ || ||
|x || || ||
+-+---+++ +--++-+++
| | | |
|Leaf111| |Leaf112|
+-------+ +-------+
Figure 32: Balancing Bandwidth
Figure 32 depicts an example topology where links between leaf and
spine nodes are 10 MBit/s and links from spine nodes northbound are
100 MBit/s. It includes parallel link failure between Leaf 111 and
Spine 111 and as a result, Leaf 111 wants to forward more traffic
toward Spine 112. Additionally, it includes as well an uplink
failure on Spine 111.
The local modification of the received default route distance from
upper level is achieved by running a relatively simple algorithm
where the bandwidth is weighted exponentially, while the distance on
the default route represents a multiplier for the bandwidth weight
for easy operational adjustments.
On a node, L, use Node TIEs to compute from each non-overloaded
northbound neighbor N to compute 3 values:
L_N_u: sum of the bandwidth available from L to N (to account for
parallel links)
N_u: sum of the uplink bandwidth available on N
T_N_u: L_N_u * OVERSUBSCRIPTION_CONSTANT + N_u
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For all T_N_u determine the corresponding M_N_u as
log_2(next_power_2(T_N_u)) and determine MAX_M_N_u as maximum value
of all such M_N_u values.
For each advertised default route from a node N modify the advertised
distance D to BAD = D * (1 + MAX_M_N_u - M_N_u) and use BAD instead
of distance D to weight balance default forwarding towards N.
For the example above, a simple table of values will help in
understanding of the concept. The implicit assumption here is that
all default route distances are advertised with D=1 and that
OVERSUBSCRIPTION_CONSTANT = 1.
+=========+===========+=======+=======+=====+
| Node | N | T_N_u | M_N_u | BAD |
+=========+===========+=======+=======+=====+
| Leaf111 | Spine 111 | 110 | 7 | 2 |
+---------+-----------+-------+-------+-----+
| Leaf111 | Spine 112 | 220 | 8 | 1 |
+---------+-----------+-------+-------+-----+
| Leaf112 | Spine 111 | 120 | 7 | 2 |
+---------+-----------+-------+-------+-----+
| Leaf112 | Spine 112 | 220 | 8 | 1 |
+---------+-----------+-------+-------+-----+
Table 6: BAD Computation
If a calculation produces a result exceeding the range of the type,
e.g. bandwidth, the result is set to the highest possible value for
that type.
BAD SHOULD only be computed for default routes. A node MAY compute
and use BAD for any disaggregated prefixes or other RIFT routes. A
node MAY use a different algorithm to weight northbound traffic based
on bandwidth. If a different algorithm is used, its successful
behavior MUST NOT depend on uniformity of algorithm or
synchronization of BAD computations across the fabric. E.g. it is
conceivable that leaves could use real time link loads gathered by
analytics to change the amount of traffic assigned to each default
route next hop.
A change in available bandwidth will only affect, at most, two levels
down in the fabric, i.e., the blast radius of bandwidth adjustments
is constrained no matter the fabric's height.
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6.8.7.2. Southbound Direction
Due to its loop free nature, during South SPF, a node MAY account for
maximum available bandwidth on nodes in lower levels and modify the
amount of traffic offered to the next level's southbound nodes. It
is worth considering that such computations may be more effective if
standardized, but do not have to be. As long as a packet continues
to flow southbound, it will take some viable, loop-free path to reach
its destination.
6.8.8. Label Binding
A node MAY advertise in its LIEs, a locally significant, downstream
assigned, interface specific label. One use of such a label is a
hop-by-hop encapsulation allowing forwarding planes to be easily
distinguished among multiple RIFT instances.
6.8.9. Leaf to Leaf Procedures
RIFT implementations SHOULD support special East-West adjacencies
between leaf nodes. Leaf nodes supporting these procedures MUST:
advertise the LEAF_2_LEAF flag in its node capabilities *and*
set the overload flag on all leaf's Node TIEs *and*
flood only a node's own north and south TIEs over E-W leaf
adjacencies *and*
always use E-W leaf adjacency in all SPF computations *and*
install a discard route for any advertised aggregate routes in a
leaf's TIE *and*
never form southbound adjacencies.
This will allow the E-W leaf nodes to exchange traffic strictly for
the prefixes advertised in each other's north prefix TIEs since the
southbound computation will find the reverse direction in the other
node's TIE and install its north prefixes.
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6.8.10. Address Family and Multi Topology Considerations
Multi-Topology (MT)[RFC5120] and Multi-Instance (MI)[RFC8202]
concepts are used today in link-state routing protocols to support
several domains on the same physical topology. RIFT supports this
capability by carrying transport ports in the LIE protocol exchanges.
Multiplexing of LIEs can be achieved by either choosing varying
multicast addresses or ports on the same address.
BFD interactions in Section 6.8.6 are implementation dependent when
multiple RIFT instances run on the same link.
6.8.11. One-Hop Healing of Levels with East-West Links
Based on the rules defined in Section 6.4, Section 6.3.8 and given
the presence of E-W links, RIFT can provide a one-hop protection for
nodes that have lost all their northbound links. This can also be
applied to multi-plane designs where complex link set failures occur
at the ToF when links are exclusively used for flooding topology
information. Section 7.4 outlines this behavior.
6.9. Security
6.9.1. Security Model
An inherent property of any security and ZTP architecture is the
resulting trade-off in regard to integrity verification of the
information distributed through the fabric vs. provisioning and auto-
configuration requirements. At a minimum the security of an
established adjacency should be ensured. The stricter the security
model the more provisioning must take over the role of ZTP.
RIFT supports the following security models to allow for flexible
control by the operator.
* The most security conscious operators may choose to have control
over which ports interconnect between a given pair of nodes, such
a model is called the "Port-Association Model" (PAM). This is
achievable by configuring each pair of directly connected ports
with a designated shared key or public/private key pair.
* In physically secure data center locations, operators may choose
to control connectivity between entire nodes, called here the
"Node-Association Model" (NAM). A benefit of this model is that
it allows for simplified port sparing.
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* In the most relaxed environments, an operator may only choose to
control which nodes join a particular fabric. This is denoted as
the "Fabric-Association Model" (FAM). This is achievable by using
a single shared secret across the entire fabric. Such flexibility
makes sense when servers are considered as leaf devices, as those
are replaced more often than network nodes. In addition, this
model allows for simplified node sparing.
* These models may be mixed throughout the fabric depending upon
security requirements at various levels of the fabric and
willingness to accept increased provisioning complexity.
In order to support the cases mentioned above, RIFT implementations
supports, through operator control, mechanisms that allow for:
a. specification of the appropriate level in the fabric,
b. discovery and reporting of missing connections,
c. discovery and reporting of unexpected connections while
preventing them from forming insecure adjacencies.
Operators may only choose to configure the level of each node, but
not explicitly configure which connections are allowed. In this
case, RIFT will only allow adjacencies to establish between nodes
that are in adjacent levels. Operators with the lowest security
requirements may not use any configuration to specify which
connections are allowed. Nodes in such fabrics could rely fully on
ZTP and only established adjacencies between nodes in adjacent
levels. Figure 33 illustrates inherent tradeoffs between the
different security models.
Some level of link quality verification may be required prior to an
adjacency being used for forwarding. For example, an implementation
may require that a BFD session comes up before advertising the
adjacency.
For the cases outlined above, RIFT has two approaches to enforce that
a local port is connected to the correct port on the correct remote
node. One approach is to piggy-back on RIFT's authentication
mechanism. Assuming the provisioning model (e.g. YANG) is flexible
enough, operators can choose to provision a unique authentication key
for the following conceptual models:
a. each pair of ports in "port-association model" or
b. each pair of switches in "node-association model" or
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c. the entire fabric in "fabric-association model".
The other approach is to rely on the System ID, port-id and level
fields in the LIE message to validate an adjacency against the
expected cabling topology, and optionally introduce some new rules in
the FSM to allow the adjacency to come up if the expectations are
met.
^ /\ |
/|\ / \ |
| / \ |
| / PAM \ |
Increasing / \ Increasing
Integrity +----------+ Flexibility
& / NAM \ &
Increasing +--------------+ Less
Provisioning / FAM \ Configuration
| / \ |
| +--------------------+ \|/
| / Zero Configuration \ v
+------------------------+
Figure 33: Security Model
6.9.2. Security Mechanisms
RIFT Security goals are to ensure:
1. authentication
2. message integrity
3. the prevention of replay attacks
4. low processing overhead
5. efficient messaging
Message confidentiality is a non-goal.
The model in the previous section allows a range of security key
types that are analogous to the various security association models.
PAM and NAM allow security associations at the port or node level
using symmetric or asymmetric keys that are pre-installed. FAM
argues for security associations to be applied only at a group level
or to be refined once the topology has been established. RIFT does
not specify how security keys are installed or updated, though it
does specify how the key can be used to achieve security goals.
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The protocol has provisions for "weak" nonces to prevent replay
attacks and includes authentication mechanisms comparable to
[RFC5709] and [RFC7987].
6.9.3. Security Envelope
A serialized schema _ProtocolPacket_ MUST be carried in a secure
envelope illustrated in Figure 34. The _ProtocolPacket_ MUST be
serialized using the default Thrift's Binary Protocol. Any value in
the packet following a security fingerprint MUST be used by a
receiver only after the appropriate fingerprint has been validated
against the data covered by it and the advertised key. This means
that for all packets, in case the node is configured to validate the
outer fingerprint, an invalid fingerprint will lead to packet
rejection. Further, in case of reception of a TIE, and the receiver
being configured to validate the originator by checking the TIE
Origin Security Envelope Header fingerprint, an invalid inner
fingerprint will lead to the rejection of the packet.
Local configuration MAY allow for the envelope's integrity checks to
be skipped.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
UDP Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | RIFT destination port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UDP Length | UDP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Outer Security Envelope Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RIFT MAGIC | Packet Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | RIFT Major | Outer Key ID | Fingerprint |
| | Version | | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Security Fingerprint covers all following content ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Weak Nonce Local | Weak Nonce Remote |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remaining TIE Lifetime (all 1s in case of LIE) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TIE Origin Security Envelope Header:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TIE Origin Key ID | Fingerprint |
| | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Security Fingerprint covers all following content ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Serialized RIFT Model Object
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Serialized RIFT Model Object ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 34: Security Envelope
RIFT MAGIC:
16 bits. Constant value of 0xA1F7 that allows easy classification
of RIFT packets independent of the UDP port used.
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Packet Number:
16 bits. An optional, per adjacency, per packet type number set
using the sequence number arithmetic defined in Appendix A. If
the arithmetic in Appendix A is not used the node MUST set the
value to _undefined_packet_number_. This number can be used to
detect losses and misordering in flooding for either operational
purposes or in implementation to adjust flooding behavior to
current link or buffer quality. This number MUST NOT be used to
discard or validate the correctness of packets. Packet numbers
are incremented on each interface and within that for each type of
packet independently. This allows parallelizing packet generation
and processing for different types within an implementation if so
desired.
RIFT Major Version:
8 bits. It allows checking whether protocol versions are
compatible, i.e., if the serialized object can be decoded at all.
An implementation MUST drop packets with unexpected values and MAY
report a problem. The specification of how an implementation
negotiates the schema's major version is outside the scope of this
document.
Outer Key ID:
8 bits to allow key rollovers. This implies key type and
algorithm. Value _invalid_key_value_key_ means that no valid
fingerprint was computed. This Key ID scope is local to the nodes
on both ends of the adjacency.
TIE Origin Key ID:
24 bits. This implies key type and used algorithm. Value
_invalid_key_value_key_ means that no valid fingerprint was
computed. This Key ID scope is global to the RIFT instance since
it may imply the originator of the TIE so the contained object
does not have to be de-serialized to obtain the originator.
Length of Fingerprint:
8 bits. Length in 32-bit multiples of the following fingerprint
(not including lifetime or weak nonces). It allows the structure
to be navigated when an unknown key type is present. To clarify,
a common corner case when this value is set to 0 is when it
signifies an empty (0 bytes long) security fingerprint.
Security Fingerprint:
32 bits * Length of Fingerprint. This is a signature that is
computed over all data following after it. If the significant
bits of fingerprint are fewer than the 32 bits padded length then
the significant bits MUST be left aligned and remaining bits on
the right padded with 0s. When using PKI (Public Key
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Infrastructure) the Security fingerprint originating node uses its
private key to create the signature. The original packet can then
be verified provided the public key is shared and current.
Methodology to negotiate, distribute, or roll over keys are
outside the scope of this document.
Remaining TIE Lifetime:
32 bits. In case of anything but TIEs this field MUST be set to
all ones and Origin Security Envelope Header MUST NOT be present
in the packet. For TIEs this field represents the remaining
lifetime of the TIE and Origin Security Envelope Header MUST be
present in the packet.
Weak Nonce Local:
16 bits. Local Weak Nonce of the adjacency as advertised in LIEs.
Weak Nonce Remote:
16 bits. Remote Weak Nonce of the adjacency as received in LIEs.
TIE Origin Security Envelope Header:
It MUST be present if and only if the Remaining TIE Lifetime field
is *not* all ones. It carries through the originators Key ID and
corresponding fingerprint of the object to protect TIE from
modification during flooding. This ensures origin validation and
integrity (but does not provide validation of a chain of trust).
Observe that due to the schema migration rules per Appendix B the
contained model can be always decoded if the major version matches
and the envelope integrity has been validated. Consequently,
description of the TIE is available to flood it properly including
unknown TIE types.
6.9.4. Weak Nonces
The protocol uses two 16-bit nonces to salt generated signatures.
The term "nonce" is used a bit loosely since RIFT nonces are not
being changed in every packet as often common in cryptography. For
efficiency purposes they are changed at a high enough frequency to
dwarf practical replay attack attempts. And hence, such nonces are
called from this point on "weak" nonces.
Any implementation including RIFT security MUST generate and wrap
around local nonces properly. When a nonce increment leads to
_undefined_nonce_ value, the value MUST be incremented again
immediately. All implementations MUST reflect the neighbor's nonces.
An implementation SHOULD increment a chosen nonce on every LIE FSM
transition that ends up in a different state from the previous one
and MUST increment its nonce at least every
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_nonce_regeneration_interval_ (such considerations allow for
efficient implementations without opening a significant security
risk). When flooding TIEs, the implementation MUST use recent (i.e.
within allowed difference) nonces reflected in the LIE exchange. The
schema specifies in _maximum_valid_nonce_delta_ the maximum allowable
nonce value difference on a packet compared to reflected nonces in
the LIEs. Any packet received with nonces deviating more than the
allowed delta MUST be discarded without further computation of
signatures to prevent computation load attacks. The delta is either
a negative or positive difference that a mirrored nonce can deviate
from local value to be considered valid. If nonces are not changed
on every packet but at the maximum interval on both sides this opens
statistically a _maximum_valid_nonce_delta_/2 window for identical
LIEs, TIE and TI(x)E replays. The interval cannot be too small since
LIE FSM may change states fairly quickly during ZTP without sending
LIEs and additionally, UDP can both loose as well as misorder
packets.
In cases where a secure implementation does not receive signatures or
receives undefined nonces from a neighbor (indicating that it does
not support or verify signatures), it is a matter of local policy as
to how those packets are treated. A secure implementation MAY refuse
forming an adjacency with an implementation that is not advertising
signatures or valid nonces, or it MAY continue signing local packets
while accepting a neighbor's packets without further security
validation.
As a necessary exception, an implementation MUST advertise the remote
nonce value as _undefined_nonce_ when the FSM is not in _TwoWay_ or
_ThreeWay_ state and accept an _undefined_nonce_ for its local nonce
value on packets in any other state than _ThreeWay_.
As an optional optimization, an implementation MAY send one LIE with
previously negotiated neighbor's nonce to try to speed up a
neighbor's transition from _ThreeWay_ to _OneWay_ and MUST revert to
sending _undefined_nonce_ after that.
6.9.5. Lifetime
Reflooding same TIE version quickly with small variations in its
lifetime may lead to an excessive number of security fingerprint
computations. To avoid this, the application generating the
fingerprints for flooded TIEs MAY round the value down to the next
_rounddown_lifetime_interval_ on the packet header to reuse previous
computation results. TIEs flooded with such rounded lifetimes only
will limit the amount of computations necessary during transitions
that lead to advertisement of same TIEs with same information within
a short period of time.
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6.9.6. Security Association Changes
There in no mechanism to convert a security envelope for the same Key
ID from one algorithm to another once the envelope is operational.
The recommended procedure to change to a new algorithm is to take the
adjacency down, make the necessary changes, and bring the adjacency
back up. Obviously, an implementation MAY choose to stop verifying
security envelope for the duration of algorithm change to keep the
adjacency up but since this introduces a security vulnerability
window, such roll-over SHOULD NOT be recommended.
7. Examples
7.1. Normal Operation
^ N +--------+ +--------+
Level 2 | |ToF 21| |ToF 22|
E <-*-> W ++-+--+-++ ++-+--+-++
| | | | | | | | |
S v P111/2 |P121/2 | | | |
^ ^ ^ ^ | | | |
| | | | | | | |
+--------------+ | +-----------+ | | | +---------------+
| | | | | | | |
South +-----------------------------+ | | ^
| | | | | | | All
0/0 0/0 0/0 +-----------------------------+ TIEs
v v v | | | | |
| | +-+ +<-0/0----------+ | |
| | | | | | | |
+-+----++ +-+----++ ++----+-+ ++-----++
Level 1 | | | | | | | |
|Spin111| |Spin112| |Spin121| |Spin122|
+-+---+-+ ++----+-+ +-+---+-+ ++---+--+
| | | South | | | |
| +---0/0--->-----+ 0/0 | +----------------+ |
0/0 | | | | | | |
| +---<-0/0-----+ | v | +--------------+ | |
v | | | | | | |
+-+---+-+ +--+--+-+ +-+---+-+ +---+-+-+
Level 0 | | | | | | | |
|Leaf111| |Leaf112| |Leaf121| |Leaf122|
+-+-----+ +-+---+-+ +--+--+-+ +-+-----+
+ + \ / + +
Prefix111 Prefix112 \ / Prefix121 Prefix122
multi-homed
Prefix
+---------- PoD 1 ---------+ +---------- PoD 2 ---------+
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Figure 35: Normal Case Topology
This section describes RIFT deployment in the example topology given
in Figure 35 without any node or link failures. The scenario
disregards flooding reduction for simplicity's sake and compresses
the node names in some cases to fit them into the picture better.
First, the following bi-directional adjacencies will be established:
1. ToF 21 (PoD 0) to Spine 111, Spine 112, Spine 121, and Spine 122
2. ToF 22 (PoD 0) to Spine 111, Spine 112, Spine 121, and Spine 122
3. Spine 111 to Leaf 111, Leaf 112
4. Spine 112 to Leaf 111, Leaf 112
5. Spine 121 to Leaf 121, Leaf 122
6. Spine 122 to Leaf 121, Leaf 122
Leaf 111 and Leaf 112 originate N-TIEs for Prefix 111 and Prefix 112
(respectively) to both Spine 111 and Spine 112 (Leaf 112 also
originates an N-TIE for the multi-homed prefix). Spine 111 and Spine
112 will then originate their own N-TIEs, as well as flood the N-TIEs
received from Leaf 111 and Leaf 112 to both ToF 21 and ToF 22.
Similarly, Leaf 121 and Leaf 122 originate North TIEs for Prefix 121
and Prefix 122 (respectively) to Spine 121 and Spine 122 (Leaf 121
also originates a North TIE for the multi-homed prefix). Spine 121
and Spine 122 will then originate their own North TIEs, as well as
flood the North TIEs received from Leaf 121 and Leaf 122 to both ToF
21 and ToF 22.
Spines hold only North TIEs of level 0 for their PoD, while leaves
only hold their own North TIEs while, at this point, both ToF 21 and
ToF 22 (as well as any northbound connected controllers) would have
the complete network topology.
ToF 21 and ToF 22 would then originate and flood South TIEs
containing any established adjacencies and a default IP route to all
spines. Spine 111, Spine 112, Spine 121, and Spine 122 will reflect
all Node South TIEs received from ToF 21 to ToF 22, and all Node
South TIEs from ToF 22 to ToF 21. South TIEs will not be re-
propagated southbound.
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South TIEs containing a default IP route are then originated by both
Spine 111 and Spine 112 toward Leaf 111 and Leaf 112. Similarly,
South TIEs containing a default IP route are originated by Spine 121
and Spine 122 toward Leaf 121 and Leaf 122.
At this point IP connectivity across maximum number of viable paths
has been established for all leaves, with routing information
constrained to only the minimum amount that allows for normal
operation and redundancy.
7.2. Leaf Link Failure
| | | |
+-+---+-+ +-+---+-+
| | | |
|Spin111| |Spin112|
+-+---+-+ ++----+-+
| | | |
| +---------------+ X
| | | X Failure
| +-------------+ | X
| | | |
+-+---+-+ +--+--+-+
| | | |
|Leaf111| |Leaf112|
+-------+ +-------+
+ +
Prefix111 Prefix112
Figure 36: Single Leaf Link Failure
In the event of a link failure between Spine 112 and Leaf 112, both
nodes will originate new Node TIEs that contain their connected
adjacencies, except for the one that just failed. Leaf 112 will send
a Node North TIE to Spine 111. Spine 112 will send a Node North TIE
to ToF 21 and ToF 22 as well as a new Node South TIE to Leaf 111 that
will be reflected to Spine 111. Necessary SPF recomputation will
occur, resulting in Spine 112 no longer being in the forwarding path
for Prefix 112.
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Spine 111 will also disaggregate Prefix 112 by sending new Prefix
South TIE to Leaf 111 and Leaf 112. Though disaggregation is covered
in more detail in the following section, it is worth mentioning in
this example as it further illustrates RIFT's mechanism to mitigate
traffic loss. Consider that Leaf 111 has yet to receive the more
specific (disaggregated) route from Spine 111. In such a scenario,
traffic from Leaf 111 toward Prefix 112 may still use Spine 112's
default route, causing it to traverse ToF 21 and ToF 22 back down via
Spine 111. While this behavior is suboptimal, it is transient in
nature and preferred to dropping traffic.
7.3. Partitioned Fabric
+--------+ +--------+
Level 2 |ToF 21| |ToF 22|
++-+--+-++ ++-+--+-++
| | | | | | | |
| | | | | | | 0/0
| | | | | | | |
| | | | | | | |
+--------------+ | +--- XXXXXX + | | | +---------------+
| | | | | | | |
| +-----------------------------+ | | |
0/0 | | | | | | |
| 0/0 0/0 +- XXXXXXXXXXXXXXXXXXXXXXXXX -+ |
| 1.1/16 | | | | | |
| | +-+ +-0/0-----------+ | |
| | | 1.1./16 | | | |
+-+----++ +-+-----+ ++-----0/0 ++----0/0
Level 1 | | | | | 1.1/16 | 1.1/16
|Spin111| |Spin112| |Spin121| |Spin122|
+-+---+-+ ++----+-+ +-+---+-+ ++---+--+
| | | | | | | |
| +---------------+ | | +----------------+ |
| | | | | | | |
| +-------------+ | | | +--------------+ | |
| | | | | | | |
+-+---+-+ +--+--+-+ +-+---+-+ +---+-+-+
Level 3 | | | | | | | |
|Leaf111| |Leaf112| |Leaf121| |Leaf122|
+-+-----+ ++------+ +-----+-+ +-+-----+
+ + + +
Prefix111 Prefix112 Prefix121 Prefix122
1.1/16
Figure 37: Fabric Partition
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Figure 37 shows one of more catastrophic scenarios where ToF 21 is
completely severed from access to Prefix 121 due to a double link
failure. If only default routes existed, this would result in 50% of
traffic from Leaf 111 and Leaf 112 toward Prefix 121 being dropped.
The mechanism to resolve this scenario hinges on ToF 21's South TIEs
being reflected from Spine 111 and Spine 112 to ToF 22. Once ToF 22
is informed that Prefix 121 cannot be reached from ToF 21, it will
begin to disaggregate Prefix 121 by advertising a more specific route
(1.1/16) along with the default IP prefix route to all spines (ToF 21
still only sends a default route). The result is Spine 111 and
Spine112 using the more specific route to Prefix 121 via ToF 22. All
other prefixes continue to use the default IP prefix route toward
both ToF 21 and ToF 22.
The more specific route for Prefix 121 being advertised by ToF 22
does not need to be propagated further south to the leaves, as they
do not benefit from this information. Spine 111 and Spine 112 are
only required to reflect the new South Node TIEs received from ToF 22
to ToF 21. In short, only the relevant nodes received the relevant
updates, thereby restricting the failure to only the partitioned
level rather than burdening the whole fabric with the flooding and
recomputation of the new topology information.
To finish this example, the following table shows sets computed by
ToF 22 using notation introduced in Section 6.5:
|R = Prefix 111, Prefix 112, Prefix 121, Prefix 122
|H (for r=Prefix 111) = Spine 111, Spine 112
|H (for r=Prefix 112) = Spine 111, Spine 112
|H (for r=Prefix 121) = Spine 121, Spine 122
|H (for r=Prefix 122) = Spine 121, Spine 122
|A (for ToF 21) = Spine 111, Spine 112
With that and |H (for r=Prefix 121) and |H (for r=Prefix 122) being
disjoint from |A (for ToF 21), ToF 22 will originate a South TIE with
Prefix 121 and Prefix 122, which will be flooded to all spines.
7.4. Northbound Partitioned Router and Optional East-West Links
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+ + +
X N1 | N2 | N3
X | |
+--+----+ +--+----+ +--+-----+
| |0/0> <0/0| |0/0> <0/0| |
| A01 +----------+ A02 +----------+ A03 | Level 1
++-+-+--+ ++--+--++ +---+-+-++
| | | | | | | | |
| | +----------------------------------+ | | |
| | | | | | | | |
| +-------------+ | | | +--------------+ |
| | | | | | | | |
| +----------------+ | +-----------------+ |
| | | | | | | | |
| | +------------------------------------+ | |
| | | | | | | | |
++-+-+--+ | +---+---+ | +-+---+-++
| | +-+ +-+ | |
| L01 | | L02 | | L03 | Level 0
+-------+ +-------+ +--------+
Figure 38: North Partitioned Router
Figure 38 shows a part of a fabric where level 1 is horizontally
connected and A01 lost its only northbound adjacency. Based on N-SPF
rules in Section 6.4.1 A01 will compute northbound reachability by
using the link A01 to A02. A02 however, will *not* use this link
during N-SPF. The result is A01 utilizing the horizontal link for
default route advertisement and unidirectional routing.
Furthermore, if A02 also loses its only northbound adjacency (N2),
the situation evolves. A01 will no longer have northbound
reachability while it receives A03's northbound adjacencies in South
Node TIEs reflected by nodes south of it. As a result, A01 will no
longer advertise its default route in accordance with Section 6.3.8.
8. Further Details on Implementation
8.1. Considerations for Leaf-Only Implementation
RIFT can and is intended to be stretched to the lowest level in the
IP fabric to integrate ToRs or even servers. Since those entities
would run as leaves only, it is worth to observe that a leaf only
version is significantly simpler to implement and requires much less
resources:
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1. Leaf nodes only need to maintain a multipath default route under
normal circumstances. However, in cases of catastrophic
partitioning, leaf nodes SHOULD be capable of accommodating all
the leaf routes in their own PoD to prevent traffic loss.
2. Leaf nodes hold only their own North TIEs and the South TIEs of
Level 1 nodes they are connected to.
3. Leaf nodes do not have to support any type of disaggregation
computation or propagation.
4. Leaf nodes are not required to support the overload flag.
5. Leaf nodes do not need to originate S-TIEs unless optional leaf-
2-leaf features are desired.
8.2. Considerations for Spine Implementation
Nodes that do not act as ToF are not required to discover fallen
leaves by comparing reachable destinations with peers and therefore
do not need to run the computation of disaggregated routes based on
that discovery. On the other hand, non-ToF nodes need to respect
disaggregated routes advertised from the north. In the case of
negative disaggregation, spines nodes need to generate southbound
disaggregated routes when all parents are lost for a fallen leaf.
9. Security Considerations
9.1. General
One can consider attack vectors where a router may reboot many times
while changing its System ID and pollute the network with many stale
TIEs or TIEs that are sent with very long lifetimes and not cleaned
up when the routes vanish. Those attack vectors are not unique to
RIFT. Given large memory footprints available today those attacks
should be relatively benign. Otherwise, a node SHOULD implement a
strategy of discarding contents of all TIEs that were not present in
the SPF tree over a certain, configurable period of time. Since the
protocol is self-stabilizing and will advertise the presence of such
TIEs to its neighbors, they can be re-requested again if a
computation finds that it has an adjacency formed towards the System
ID of the discarded TIEs.
9.2. Time to Live and Hop Limit Values
RIFT explicitly requires the use of a TTL/HL value of 1 *or* 255 when
sending/receiving LIEs and TIEs so that implementors have a choice
between the two.
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Using a TTL/HL value of 255 does come with security concerns, but
those risks are addressed in [RFC5082]. However, this approach may
still have difficulties with some forwarding implementations (e.g.
incorrectly processing TTL/HL, loops within forwarding plane itself,
etc.).
It is for this reason that RIFT also allows implementations to use a
TTL/HL of 1. Attacks that exploit this by spoofing it from several
hops away are indeed possible, but are exceptionally difficult to
engineer. Replay attacks are another potential attack vector, but as
described in the subsequent security sections, RIFT is well protected
against such attacks.
9.3. Malformed Packets
The protocol protects packets extensively through optional signatures
and nonces so if the possibility of maliciously injected malformed or
replayed packets exist in a deployment, this conclusively protects
against such attacks.
Even with the security envelope, since RIFT relies on Thrift encoders
and decoders generated automatically from IDL it is conceivable that
errors in such encoders/decoders could be discovered and lead to
delivery of corrupted packets or reception of packets that cannot be
decoded. Misformatted packets lead normally to decoder returning an
error condition to the caller and with that the packet is basically
unparsable with no other choice but to discard it. Should the
unlikely scenario occur of the decoder being forced to abort the
protocol this is neither better nor worse than today's behavior of
other protocols.
9.4. ZTP
Section 6.7 presents many attack vectors in untrusted environments,
starting with nodes that oscillate their level offers to the
possibility of nodes offering a _ThreeWay_ adjacency with the highest
possible level value and a very long holdtime trying to put itself
"on top of the lattice" thereby allowing it to gain access to the
whole southbound topology. Session authentication mechanisms are
necessary in environments where this is possible and RIFT provides
the security envelope to ensure this if so desired.
9.5. Lifetime
RIFT removes lifetime modification and replay attack vectors by
protecting the lifetime behind a signature computed over it and
additional nonce combination which results in the inability of an
attacker to artificially shorten the _remaining_lifetime_.
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9.6. Packet Number
An optional defined value number that is carried in the security
envelope without any encryption protection and is hence vulnerable to
replay and modification attacks. Contrary to nonces, this number
must change on every packet and would present a very high
cryptographic load if signed. The attack vector packet number
present is relatively benign. Changing the packet number by a man-
in-the-middle attack will only affect operational validation tools
and possibly some performance optimizations on flooding. It is
expected that an implementation detecting too many "fake losses" or
"misorderings" due to the attack on the packet number would simply
suppress its further processing.
9.7. Outer Fingerprint Attacks
A node can try to inject LIE packets observing a conversation on the
wire by using the outer Key ID albeit it cannot generate valid hashes
in case it changes the integrity of the message so the only possible
attack is DoS due to excessive LIE validation.
A node can try to replay previous LIEs with changed state that it
recorded but the attack is hard to replicate since the nonce
combination must match the ongoing exchange and is then limited to a
single flap only since both nodes will advance their nonces in case
the adjacency state changed. Even in the most unlikely case the
attack length is limited due to both sides periodically increasing
their nonces.
Generally, since weak nonces are not changed on every packet for
performance reasons a conceivable attack vector by a man-in-the-
middle is to flood a receiving node with maximum bandwidth of
recently observed packets, both LIEs as well as TIEs. In a scenario
where such attacks are likely _maximum_valid_nonce_delta_ can be
implemented as configurable, small value and
_nonce_regeneration_interval_ configured to very small value as well.
This will likely present a significant computational load on large
fabrics under normal operation.
9.8. TIE Origin Fingerprint DoS Attacks
A compromised node can attempt to generate "fake TIEs" using other
nodes' TIE origin key identifiers. Albeit the ultimate validation of
the origin fingerprint will fail in such scenarios and not progress
further than immediately peering nodes, the resulting denial of
service attack seems unavoidable since the TIE origin Key ID is only
protected by the, here assumed to be compromised, node.
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9.9. Host Implementations
It can be reasonably expected that with the proliferation of RotH
servers, rather than dedicated networking devices, will represent a
significant amount of RIFT devices. Given their normally far wider
software envelope and access granted to them, such servers are also
far more likely to be compromised and present an attack vector on the
protocol. Hijacking of prefixes to attract traffic is a trust
problem and cannot be easily addressed within the protocol if the
trust model is breached, i.e. the server presents valid credentials
to form an adjacency and issue TIEs. In an even more devious way,
the servers can present DoS (or even DDoS) vectors of issuing too
many LIE packets, flooding large amounts of North TIEs, and
attempting similar resource overrun attacks. A prudent
implementation forming adjacencies to leaves should implement
thresholds mechanisms and raise warnings when, e.g., a leaf is
advertising an excess number of TIEs or prefixes. Additionally, such
implementation could refuse any topology information except the
node's own TIEs and authenticated, reflected South Node TIEs at own
level.
To isolate possible attack vectors on the leaf to the largest
possible extent a dedicated leaf-only implementation could run
without any configuration by hard-coding a well-known adjacency key
(which can be always rolled-over by the means of, e.g., well-known
key-value distributed from top of the fabric), leaf level value and
always setting overload flag. All other values can be derived by
automatic means as described above.
9.9.1. IPv4 Broadcast and IPv6 All Routers Multicast Implementations
Section 6.2 describes an optional implementation that supports LIE
exchange over IPv4 broadcast addresses and/or the IPv6 all routers
multicast address. It is important to consider that if an
implementation supports this, the attack surface widens as LIEs may
be propagated to devices outside of the intended RIFT topology. This
may leave RIFT nodes susceptible to the various attack vectors
already described in this section.
10. IANA Considerations
This specification requests multicast address assignments and
standard port numbers. Additionally registries for the schema are
requested and suggested values provided that reflect the numbers
allocated in the given schema.
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10.1. Requested Multicast and Port Numbers
This document requests allocation in the 'IPv4 Multicast Address
Space' registry the suggested value of 224.0.0.121 as
'ALL_V4_RIFT_ROUTERS' and in the 'IPv6 Multicast Address Space'
registry the suggested value of FF02::A1F7 as 'ALL_V6_RIFT_ROUTERS'.
This document requests allocation in the 'Service Name and Transport
Protocol Port Number Registry' the allocation of a suggested value of
914 on UDP for 'RIFT_LIES_PORT' and suggested value of 915 for
'RIFT_TIES_PORT'.
10.2. Requested Registries with Assigned Values
This section requests registries that help govern the schema via
usual IANA registry procedures. A top-level group named 'RIFT'
should hold the corresponding registries requested in the following
sections with their pre-defined values. Registry values are stored
with their minimum and maximum version in which they are available.
All values not provided are to be considered _Unassigned_. The range
of every registry is a 16-bit integer. Allocation of new values is
always performed via `Expert Review` action.
10.2.1. Expert Review Guidance
Experts reviewing requests for new values in the RIFT registry are
responsible for the following:
1. Determining the existence of a specification that clearly defines
the purpose supporting the request and MUST contain all required
fields for given registry.
The document MUST also be permanent and publicly available.
2. Ensuring that any requests are made available to the RIFT working
group for review should the work originate from outside of the
RIFT Working Group.
3. Ensuring that any work produce outside of the IETF does not
conflict with any work that is already published or actively
pursuing being published.
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10.2.2. Registry RIFT/Versions
This registry stores all RIFT protocol schema major and minor
versions including the reference to the document introducing the
version. This means as well that if multiple documents extend rift
schema they have to serialize using this registry to increase the
minor or major versions sequentially.
+================+===================================+
| Schema Version | Reference |
+================+===================================+
| 8.0 | https://datatracker.ietf.org/doc/ |
| | draft-ietf-rift-rift/ Appendix B |
+----------------+-----------------------------------+
Table 7
10.2.3. Registry RIFT/common/AddressFamilyType
Address family type.
+=========================+========================+
| Schema Range | Registration Procedure |
+=========================+========================+
| Major or Minor Change | Standards Action |
| per Rules in Appendix B | |
+-------------------------+------------------------+
| All Other Assignments | Specification Required |
+-------------------------+------------------------+
Table 8
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+=======================+=======+=========+=========+=============+
| Name | Value | Min. | Max. | Description |
| | | Schema | Schema | |
| | | Version | Version | |
+=======================+=======+=========+=========+=============+
| Illegal | 0 | 8.0 | | |
+-----------------------+-------+---------+---------+-------------+
| AddressFamilyMinValue | 1 | 8.0 | | |
+-----------------------+-------+---------+---------+-------------+
| IPv4 | 2 | 8.0 | | |
+-----------------------+-------+---------+---------+-------------+
| IPv6 | 3 | 8.0 | | |
+-----------------------+-------+---------+---------+-------------+
| AddressFamilyMaxValue | 4 | 8.0 | | |
+-----------------------+-------+---------+---------+-------------+
Table 9
10.2.4. Registry RIFT/common/HierarchyIndications
Flags indicating node configuration in case of ZTP.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 10
+====================================+=====+=======+=======+===========+
|Name |Value| Min.| Max.|Description|
| | | Schema| Schema| |
| | |Version|Version| |
+====================================+=====+=======+=======+===========+
|leaf_only | 0| 8.0| | |
+------------------------------------+-----+-------+-------+-----------+
|leaf_only_and_leaf_2_leaf_procedures| 1| 8.0| | |
+------------------------------------+-----+-------+-------+-----------+
|top_of_fabric | 2| 8.0| | |
+------------------------------------+-----+-------+-------+-----------+
Table 11
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10.2.5. Registry RIFT/common/IEEE802_1ASTimeStampType
Timestamp per IEEE 802.1AS, all values MUST be interpreted in
implementation as unsigned.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 12
+=========+=======+=====================+=============+=============+
| Name | Value | Min. Schema | Max. Schema | Description |
| | | Version | Version | |
+=========+=======+=====================+=============+=============+
| AS_sec | 1 | 8.0 | | |
+---------+-------+---------------------+-------------+-------------+
| AS_nsec | 2 | 8.0 | | |
+---------+-------+---------------------+-------------+-------------+
Table 13
10.2.6. Registry RIFT/common/IPAddressType
IP address type.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 14
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+=============+=======+=============+=============+=============+
| Name | Value | Min. Schema | Max. Schema | Description |
| | | Version | Version | |
+=============+=======+=============+=============+=============+
| ipv4address | 1 | 8.0 | | Content is |
| | | | | IPv4 |
+-------------+-------+-------------+-------------+-------------+
| ipv6address | 2 | 8.0 | | Content is |
| | | | | IPv6 |
+-------------+-------+-------------+-------------+-------------+
Table 15
10.2.7. Registry RIFT/common/IPPrefixType
Prefix advertisement.
@note: for interface addresses the protocol can propagate the address
part beyond the subnet mask and on reachability computation that has
to be normalized. The non-significant bits can be used for
operational purposes.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 16
+============+=======+=============+=============+=============+
| Name | Value | Min. Schema | Max. Schema | Description |
| | | Version | Version | |
+============+=======+=============+=============+=============+
| ipv4prefix | 1 | 8.0 | | |
+------------+-------+-------------+-------------+-------------+
| ipv6prefix | 2 | 8.0 | | |
+------------+-------+-------------+-------------+-------------+
Table 17
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10.2.8. Registry RIFT/common/IPv4PrefixType
IPv4 prefix type.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 18
+===========+=======+=============+=============+=============+
| Name | Value | Min. Schema | Max. Schema | Description |
| | | Version | Version | |
+===========+=======+=============+=============+=============+
| address | 1 | 8.0 | | |
+-----------+-------+-------------+-------------+-------------+
| prefixlen | 2 | 8.0 | | |
+-----------+-------+-------------+-------------+-------------+
Table 19
10.2.9. Registry RIFT/common/IPv6PrefixType
IPv6 prefix type.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 20
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+===========+=======+=============+=============+=============+
| Name | Value | Min. Schema | Max. Schema | Description |
| | | Version | Version | |
+===========+=======+=============+=============+=============+
| address | 1 | 8.0 | | |
+-----------+-------+-------------+-------------+-------------+
| prefixlen | 2 | 8.0 | | |
+-----------+-------+-------------+-------------+-------------+
Table 21
10.2.10. Registry RIFT/common/KVTypes
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 22
+==============+=======+=============+=============+=============+
| Name | Value | Min. Schema | Max. Schema | Description |
| | | Version | Version | |
+==============+=======+=============+=============+=============+
| Experimental | 1 | 8.0 | | |
+--------------+-------+-------------+-------------+-------------+
| WellKnown | 2 | 8.0 | | |
+--------------+-------+-------------+-------------+-------------+
| OUI | 3 | 8.0 | | |
+--------------+-------+-------------+-------------+-------------+
Table 23
10.2.11. Registry RIFT/common/PrefixSequenceType
Sequence of a prefix in case of move.
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+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 24
+===============+=======+=============+=========+==================+
| Name | Value | Min. Schema | Max. | Description |
| | | Version | Schema | |
| | | | Version | |
+===============+=======+=============+=========+==================+
| timestamp | 1 | 8.0 | | |
+---------------+-------+-------------+---------+------------------+
| transactionid | 2 | 8.0 | | Transaction ID |
| | | | | set by client in |
| | | | | e.g. in 6LoWPAN. |
+---------------+-------+-------------+---------+------------------+
Table 25
10.2.12. Registry RIFT/common/RouteType
RIFT route types. @note: The only purpose of those values is to
introduce an ordering whereas an implementation can choose internally
any other values as long the ordering is preserved
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 26
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+=====================+=======+=============+=========+=============+
| Name | Value | Min. | Max. | Description |
| | | Schema | Schema | |
| | | Version | Version | |
+=====================+=======+=============+=========+=============+
| Illegal | 0 | 8.0 | | |
+---------------------+-------+-------------+---------+-------------+
| RouteTypeMinValue | 1 | 8.0 | | |
+---------------------+-------+-------------+---------+-------------+
| Discard | 2 | 8.0 | | |
+---------------------+-------+-------------+---------+-------------+
| LocalPrefix | 3 | 8.0 | | |
+---------------------+-------+-------------+---------+-------------+
| SouthPGPPrefix | 4 | 8.0 | | |
+---------------------+-------+-------------+---------+-------------+
| NorthPGPPrefix | 5 | 8.0 | | |
+---------------------+-------+-------------+---------+-------------+
| NorthPrefix | 6 | 8.0 | | |
+---------------------+-------+-------------+---------+-------------+
| NorthExternalPrefix | 7 | 8.0 | | |
+---------------------+-------+-------------+---------+-------------+
| SouthPrefix | 8 | 8.0 | | |
+---------------------+-------+-------------+---------+-------------+
| SouthExternalPrefix | 9 | 8.0 | | |
+---------------------+-------+-------------+---------+-------------+
| NegativeSouthPrefix | 10 | 8.0 | | |
+---------------------+-------+-------------+---------+-------------+
| RouteTypeMaxValue | 11 | 8.0 | | |
+---------------------+-------+-------------+---------+-------------+
Table 27
10.2.13. Registry RIFT/common/TIETypeType
Type of TIE.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 28
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+===========================================+=====+=======+=======+===========+
|Name |Value| Min.| Max.|Description|
| | | Schema| Schema| |
| | |Version|Version| |
+===========================================+=====+=======+=======+===========+
|Illegal | 0| 8.0| | |
+-------------------------------------------+-----+-------+-------+-----------+
|TIETypeMinValue | 1| 8.0| | |
+-------------------------------------------+-----+-------+-------+-----------+
|NodeTIEType | 2| 8.0| | |
+-------------------------------------------+-----+-------+-------+-----------+
|PrefixTIEType | 3| 8.0| | |
+-------------------------------------------+-----+-------+-------+-----------+
|PositiveDisaggregationPrefixTIEType | 4| 8.0| | |
+-------------------------------------------+-----+-------+-------+-----------+
|NegativeDisaggregationPrefixTIEType | 5| 8.0| | |
+-------------------------------------------+-----+-------+-------+-----------+
|PGPrefixTIEType | 6| 8.0| | |
+-------------------------------------------+-----+-------+-------+-----------+
|KeyValueTIEType | 7| 8.0| | |
+-------------------------------------------+-----+-------+-------+-----------+
|ExternalPrefixTIEType | 8| 8.0| | |
+-------------------------------------------+-----+-------+-------+-----------+
|PositiveExternalDisaggregationPrefixTIEType| 9| 8.0| | |
+-------------------------------------------+-----+-------+-------+-----------+
|TIETypeMaxValue | 10| 8.0| | |
+-------------------------------------------+-----+-------+-------+-----------+
Table 29
10.2.14. Registry RIFT/common/TieDirectionType
Direction of TIEs.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 30
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+===================+=======+=============+=========+=============+
| Name | Value | Min. Schema | Max. | Description |
| | | Version | Schema | |
| | | | Version | |
+===================+=======+=============+=========+=============+
| Illegal | 0 | 8.0 | | |
+-------------------+-------+-------------+---------+-------------+
| South | 1 | 8.0 | | |
+-------------------+-------+-------------+---------+-------------+
| North | 2 | 8.0 | | |
+-------------------+-------+-------------+---------+-------------+
| DirectionMaxValue | 3 | 8.0 | | |
+-------------------+-------+-------------+---------+-------------+
Table 31
10.2.15. Registry RIFT/encoding/Community
Prefix community.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 32
+========+=======+=====================+=============+=============+
| Name | Value | Min. Schema Version | Max. Schema | Description |
| | | | Version | |
+========+=======+=====================+=============+=============+
| top | 1 | 8.0 | | Higher |
| | | | | order bits |
+--------+-------+---------------------+-------------+-------------+
| bottom | 2 | 8.0 | | Lower order |
| | | | | bits |
+--------+-------+---------------------+-------------+-------------+
Table 33
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10.2.16. Registry RIFT/encoding/KeyValueTIEElement
Generic key value pairs.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 34
+===========+=======+=============+=============+=============+
| Name | Value | Min. Schema | Max. Schema | Description |
| | | Version | Version | |
+===========+=======+=============+=============+=============+
| keyvalues | 1 | 8.0 | | |
+-----------+-------+-------------+-------------+-------------+
Table 35
10.2.17. Registry RIFT/encoding/KeyValueTIEElementContent
Defines the targeted nodes and the value carried.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 36
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+=========+=======+=====================+=============+=============+
| Name | Value | Min. Schema | Max. Schema | Description |
| | | Version | Version | |
+=========+=======+=====================+=============+=============+
| targets | 1 | 8.0 | | |
+---------+-------+---------------------+-------------+-------------+
| value | 2 | 8.0 | | |
+---------+-------+---------------------+-------------+-------------+
Table 37
10.2.18. Registry RIFT/encoding/LIEPacket
RIFT LIE Packet.
@note: this node's level is already included on the packet header
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 38
+=============================+=====+=======+=======+===============+
| Name |Value| Min.| Max.| Description |
| | | Schema| Schema| |
| | |Version|Version| |
+=============================+=====+=======+=======+===============+
| name | 1| 8.0| | Node or |
| | | | | adjacency |
| | | | | name. |
+-----------------------------+-----+-------+-------+---------------+
| local_id | 2| 8.0| | Local link |
| | | | | ID. |
+-----------------------------+-----+-------+-------+---------------+
| flood_port | 3| 8.0| | UDP port to |
| | | | | which we can |
| | | | | receive |
| | | | | flooded TIEs. |
+-----------------------------+-----+-------+-------+---------------+
| link_mtu_size | 4| 8.0| | Layer 3 MTU, |
| | | | | used to |
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| | | | | discover |
| | | | | mismatch. |
+-----------------------------+-----+-------+-------+---------------+
| link_bandwidth | 5| 8.0| | Local link |
| | | | | bandwidth on |
| | | | | the |
| | | | | interface. |
+-----------------------------+-----+-------+-------+---------------+
| neighbor | 6| 8.0| | Reflects the |
| | | | | neighbor once |
| | | | | received to |
| | | | | provide 3-way |
| | | | | connectivity. |
+-----------------------------+-----+-------+-------+---------------+
| pod | 7| 8.0| | Node's PoD. |
+-----------------------------+-----+-------+-------+---------------+
| node_capabilities | 10| 8.0| | Node |
| | | | | capabilities |
| | | | | supported. |
+-----------------------------+-----+-------+-------+---------------+
| link_capabilities | 11| 8.0| | Capabilities |
| | | | | of this link. |
+-----------------------------+-----+-------+-------+---------------+
| holdtime | 12| 8.0| | Required |
| | | | | holdtime of |
| | | | | the |
| | | | | adjacency, |
| | | | | i.e. for how |
| | | | | long a period |
| | | | | should |
| | | | | adjacency be |
| | | | | kept up |
| | | | | without valid |
| | | | | LIE |
| | | | | reception. |
+-----------------------------+-----+-------+-------+---------------+
| label | 13| 8.0| | Optional, |
| | | | | unsolicited, |
| | | | | downstream |
| | | | | assigned |
| | | | | locally |
| | | | | significant |
| | | | | label value |
| | | | | for the |
| | | | | adjacency. |
+-----------------------------+-----+-------+-------+---------------+
| not_a_ztp_offer | 21| 8.0| | Indicates |
| | | | | that the |
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| | | | | level on the |
| | | | | LIE must not |
| | | | | be used to |
| | | | | derive a ZTP |
| | | | | level by the |
| | | | | receiving |
| | | | | node. |
+-----------------------------+-----+-------+-------+---------------+
| you_are_flood_repeater | 22| 8.0| | Indicates to |
| | | | | northbound |
| | | | | neighbor that |
| | | | | it should be |
| | | | | reflooding |
| | | | | TIEs received |
| | | | | from this |
| | | | | node to |
| | | | | achieve flood |
| | | | | reduction and |
| | | | | balancing for |
| | | | | northbound |
| | | | | flooding. |
+-----------------------------+-----+-------+-------+---------------+
| you_are_sending_too_quickly | 23| 8.0| | Indicates to |
| | | | | neighbor to |
| | | | | flood node |
| | | | | TIEs only and |
| | | | | slow down all |
| | | | | other TIEs. |
| | | | | Ignored when |
| | | | | received from |
| | | | | southbound |
| | | | | neighbor. |
+-----------------------------+-----+-------+-------+---------------+
| instance_name | 24| 8.0| | Instance name |
| | | | | in case |
| | | | | multiple RIFT |
| | | | | instances |
| | | | | running on |
| | | | | same |
| | | | | interface. |
+-----------------------------+-----+-------+-------+---------------+
| fabric_id | 35| 8.0| | It provides |
| | | | | the optional |
| | | | | ID of the |
| | | | | Fabric |
| | | | | configured. |
| | | | | This MUST |
| | | | | match the |
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| | | | | information |
| | | | | advertised on |
| | | | | the node |
| | | | | element. |
+-----------------------------+-----+-------+-------+---------------+
Table 39
10.2.19. Registry RIFT/encoding/LinkCapabilities
Link capabilities.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 40
+=========================+=====+=========+=========+==============+
| Name |Value| Min. | Max. | Description |
| | | Schema | Schema | |
| | | Version | Version | |
+=========================+=====+=========+=========+==============+
| bfd | 1| 8.0 | | Indicates |
| | | | | that the |
| | | | | link is |
| | | | | supporting |
| | | | | BFD. |
+-------------------------+-----+---------+---------+--------------+
| ipv4_forwarding_capable | 2| 8.0 | | Indicates |
| | | | | whether the |
| | | | | interface |
| | | | | will support |
| | | | | IPv4 |
| | | | | forwarding. |
+-------------------------+-----+---------+---------+--------------+
Table 41
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10.2.20. Registry RIFT/encoding/LinkIDPair
LinkID pair describes one of parallel links between two nodes.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 42
+============================+=====+=======+=========+==============+
| Name |Value| Min.| Max. | Description |
| | | Schema| Schema | |
| | |Version| Version | |
+============================+=====+=======+=========+==============+
| local_id | 1| 8.0| | Node-wide |
| | | | | unique |
| | | | | value for |
| | | | | the local |
| | | | | link. |
+----------------------------+-----+-------+---------+--------------+
| remote_id | 2| 8.0| | Received |
| | | | | remote link |
| | | | | ID for this |
| | | | | link. |
+----------------------------+-----+-------+---------+--------------+
| platform_interface_index | 10| 8.0| | Describes |
| | | | | the local |
| | | | | interface |
| | | | | index of |
| | | | | the link. |
+----------------------------+-----+-------+---------+--------------+
| platform_interface_name | 11| 8.0| | Describes |
| | | | | the local |
| | | | | interface |
| | | | | name. |
+----------------------------+-----+-------+---------+--------------+
| trusted_outer_security_key | 12| 8.0| | Indicates |
| | | | | whether the |
| | | | | link is |
| | | | | secured, |
| | | | | i.e. |
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| | | | | protected |
| | | | | by outer |
| | | | | key, |
| | | | | absence of |
| | | | | this |
| | | | | element |
| | | | | means no |
| | | | | indication, |
| | | | | undefined |
| | | | | outer key |
| | | | | means not |
| | | | | secured. |
+----------------------------+-----+-------+---------+--------------+
| bfd_up | 13| 8.0| | Indicates |
| | | | | whether the |
| | | | | link is |
| | | | | protected |
| | | | | by |
| | | | | established |
| | | | | BFD |
| | | | | session. |
+----------------------------+-----+-------+---------+--------------+
| address_families | 14| 8.0| | Optional |
| | | | | indication |
| | | | | which |
| | | | | address |
| | | | | families |
| | | | | are up on |
| | | | | the |
| | | | | interface |
+----------------------------+-----+-------+---------+--------------+
Table 43
10.2.21. Registry RIFT/encoding/Neighbor
Neighbor structure.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 44
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+============+=======+=============+=============+=================+
| Name | Value | Min. Schema | Max. Schema | Description |
| | | Version | Version | |
+============+=======+=============+=============+=================+
| originator | 1 | 8.0 | | System ID of |
| | | | | the originator. |
+------------+-------+-------------+-------------+-----------------+
| remote_id | 2 | 8.0 | | ID of remote |
| | | | | side of the |
| | | | | link. |
+------------+-------+-------------+-------------+-----------------+
Table 45
10.2.22. Registry RIFT/encoding/NodeCapabilities
Capabilities the node supports.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 46
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+========================+=====+=========+=========+================+
| Name |Value| Min. | Max. | Description |
| | | Schema | Schema | |
| | | Version | Version | |
+========================+=====+=========+=========+================+
| protocol_minor_version | 1| 8.0 | | Must |
| | | | | advertise |
| | | | | supported |
| | | | | minor version |
| | | | | dialect that |
| | | | | way. |
+------------------------+-----+---------+---------+----------------+
| flood_reduction | 2| 8.0 | | indicates |
| | | | | that node |
| | | | | supports |
| | | | | flood |
| | | | | reduction. |
+------------------------+-----+---------+---------+----------------+
| hierarchy_indications | 3| 8.0 | | indicates |
| | | | | place in |
| | | | | hierarchy, |
| | | | | i.e. top-of- |
| | | | | fabric or |
| | | | | leaf only (in |
| | | | | ZTP) or |
| | | | | support for |
| | | | | leaf-2-leaf |
| | | | | procedures. |
+------------------------+-----+---------+---------+----------------+
Table 47
10.2.23. Registry RIFT/encoding/NodeFlags
Indication flags of the node.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 48
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+==========+=======+=========+=========+===========================+
| Name | Value | Min. | Max. | Description |
| | | Schema | Schema | |
| | | Version | Version | |
+==========+=======+=========+=========+===========================+
| overload | 1 | 8.0 | | Indicates that node is in |
| | | | | overload, do not transit |
| | | | | traffic through it. |
+----------+-------+---------+---------+---------------------------+
Table 49
10.2.24. Registry RIFT/encoding/NodeNeighborsTIEElement
neighbor of a node
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 50
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+===========+=======+=========+=========+==========================+
| Name | Value | Min. | Max. | Description |
| | | Schema | Schema | |
| | | Version | Version | |
+===========+=======+=========+=========+==========================+
| level | 1 | 8.0 | | level of neighbor |
+-----------+-------+---------+---------+--------------------------+
| cost | 3 | 8.0 | | Cost to neighbor. |
| | | | | Ignore anything larger |
| | | | | than _infinite_distance_ |
| | | | | and _invalid_distance_ |
+-----------+-------+---------+---------+--------------------------+
| link_ids | 4 | 8.0 | | can carry description of |
| | | | | multiple parallel links |
| | | | | in a TIE |
+-----------+-------+---------+---------+--------------------------+
| bandwidth | 5 | 8.0 | | total bandwith to |
| | | | | neighbor as sum of all |
| | | | | parallel links |
+-----------+-------+---------+---------+--------------------------+
Table 51
10.2.25. Registry RIFT/encoding/NodeTIEElement
Description of a node.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 52
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+=================+=======+=========+=========+====================+
| Name | Value | Min. | Max. | Description |
| | | Schema | Schema | |
| | | Version | Version | |
+=================+=======+=========+=========+====================+
| level | 1 | 8.0 | | Level of the node. |
+-----------------+-------+---------+---------+--------------------+
| neighbors | 2 | 8.0 | | Node's neighbors. |
| | | | | Multiple node TIEs |
| | | | | can carry disjoint |
| | | | | sets of neighbors. |
+-----------------+-------+---------+---------+--------------------+
| capabilities | 3 | 8.0 | | Capabilities of |
| | | | | the node. |
+-----------------+-------+---------+---------+--------------------+
| flags | 4 | 8.0 | | Flags of the node. |
+-----------------+-------+---------+---------+--------------------+
| name | 5 | 8.0 | | Optional node name |
| | | | | for easier |
| | | | | operations. |
+-----------------+-------+---------+---------+--------------------+
| pod | 6 | 8.0 | | PoD to which the |
| | | | | node belongs. |
+-----------------+-------+---------+---------+--------------------+
| startup_time | 7 | 8.0 | | optional startup |
| | | | | time of the node |
+-----------------+-------+---------+---------+--------------------+
| miscabled_links | 10 | 8.0 | | If any local links |
| | | | | are miscabled, |
| | | | | this indication is |
| | | | | flooded. |
+-----------------+-------+---------+---------+--------------------+
| same_plane_tofs | 12 | 8.0 | | ToFs in the same |
| | | | | plane. Only |
| | | | | carried by ToF. |
| | | | | Multiple Node TIEs |
| | | | | can carry disjoint |
| | | | | sets of ToFs which |
| | | | | MUST be joined to |
| | | | | form a single set. |
+-----------------+-------+---------+---------+--------------------+
| fabric_id | 20 | 8.0 | | It provides the |
| | | | | optional ID of the |
| | | | | Fabric configured |
+-----------------+-------+---------+---------+--------------------+
Table 53
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10.2.26. Registry RIFT/encoding/PacketContent
Content of a RIFT packet.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 54
+======+=======+=====================+=============+=============+
| Name | Value | Min. Schema Version | Max. Schema | Description |
| | | | Version | |
+======+=======+=====================+=============+=============+
| lie | 1 | 8.0 | | |
+------+-------+---------------------+-------------+-------------+
| tide | 2 | 8.0 | | |
+------+-------+---------------------+-------------+-------------+
| tire | 3 | 8.0 | | |
+------+-------+---------------------+-------------+-------------+
| tie | 4 | 8.0 | | |
+------+-------+---------------------+-------------+-------------+
Table 55
10.2.27. Registry RIFT/encoding/PacketHeader
Common RIFT packet header.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 56
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+===============+=======+=========+=========+===================+
| Name | Value | Min. | Max. | Description |
| | | Schema | Schema | |
| | | Version | Version | |
+===============+=======+=========+=========+===================+
| major_version | 1 | 8.0 | | Major version of |
| | | | | protocol. |
+---------------+-------+---------+---------+-------------------+
| minor_version | 2 | 8.0 | | Minor version of |
| | | | | protocol. |
+---------------+-------+---------+---------+-------------------+
| sender | 3 | 8.0 | | Node sending the |
| | | | | packet, in case |
| | | | | of LIE/TIRE/TIDE |
| | | | | also the |
| | | | | originator of it. |
+---------------+-------+---------+---------+-------------------+
| level | 4 | 8.0 | | Level of the node |
| | | | | sending the |
| | | | | packet, required |
| | | | | on everything |
| | | | | except LIEs. |
| | | | | Lack of presence |
| | | | | on LIEs indicates |
| | | | | UNDEFINED_LEVEL |
| | | | | and is used in |
| | | | | ZTP procedures. |
+---------------+-------+---------+---------+-------------------+
Table 57
10.2.28. Registry RIFT/encoding/PrefixAttributes
Attributes of a prefix.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 58
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+===================+=======+=========+=========+===================+
| Name | Value | Min. | Max. | Description |
| | | Schema | Schema | |
| | | Version | Version | |
+===================+=======+=========+=========+===================+
| metric | 2 | 8.0 | | Distance of the |
| | | | | prefix. |
+-------------------+-------+---------+---------+-------------------+
| tags | 3 | 8.0 | | Generic |
| | | | | unordered set of |
| | | | | route tags, can |
| | | | | be redistributed |
| | | | | to other |
| | | | | protocols or use |
| | | | | within the |
| | | | | context of real |
| | | | | time analytics. |
+-------------------+-------+---------+---------+-------------------+
| monotonic_clock | 4 | 8.0 | | Monotonic clock |
| | | | | for mobile |
| | | | | addresses. |
+-------------------+-------+---------+---------+-------------------+
| loopback | 6 | 8.0 | | Indicates if the |
| | | | | prefix is a node |
| | | | | loopback. |
+-------------------+-------+---------+---------+-------------------+
| directly_attached | 7 | 8.0 | | Indicates that |
| | | | | the prefix is |
| | | | | directly |
| | | | | attached. |
+-------------------+-------+---------+---------+-------------------+
| from_link | 10 | 8.0 | | link to which |
| | | | | the address |
| | | | | belongs to. |
+-------------------+-------+---------+---------+-------------------+
| label | 12 | 8.0 | | Optional, per |
| | | | | prefix |
| | | | | significant |
| | | | | label. |
+-------------------+-------+---------+---------+-------------------+
Table 59
10.2.29. Registry RIFT/encoding/PrefixTIEElement
TIE carrying prefixes
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+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 60
+==========+=======+=============+=============+================+
| Name | Value | Min. Schema | Max. Schema | Description |
| | | Version | Version | |
+==========+=======+=============+=============+================+
| prefixes | 1 | 8.0 | | Prefixes with |
| | | | | the associated |
| | | | | attributes. |
+----------+-------+-------------+-------------+----------------+
Table 61
10.2.30. Registry RIFT/encoding/ProtocolPacket
RIFT packet structure.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 62
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+=========+=======+=====================+=============+=============+
| Name | Value | Min. Schema | Max. Schema | Description |
| | | Version | Version | |
+=========+=======+=====================+=============+=============+
| header | 1 | 8.0 | | |
+---------+-------+---------------------+-------------+-------------+
| content | 2 | 8.0 | | |
+---------+-------+---------------------+-------------+-------------+
Table 63
10.2.31. Registry RIFT/encoding/TIDEPacket
TIDE with *sorted* TIE headers.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 64
+=============+=======+=============+=============+===============+
| Name | Value | Min. Schema | Max. Schema | Description |
| | | Version | Version | |
+=============+=======+=============+=============+===============+
| start_range | 1 | 8.0 | | First TIE |
| | | | | header in the |
| | | | | tide packet. |
+-------------+-------+-------------+-------------+---------------+
| end_range | 2 | 8.0 | | Last TIE |
| | | | | header in the |
| | | | | tide packet. |
+-------------+-------+-------------+-------------+---------------+
| headers | 3 | 8.0 | | _Sorted_ list |
| | | | | of headers. |
+-------------+-------+-------------+-------------+---------------+
Table 65
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10.2.32. Registry RIFT/encoding/TIEElement
Single element in a TIE.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 66
+=========================================+=====+=======+=======+=================================+
|Name |Value| Min.| Max.|Description |
| | | Schema| Schema| |
| | |Version|Version| |
+=========================================+=====+=======+=======+=================================+
|node | 1| 8.0| | Used in case of enum|
| | | | | common.TIETypeType.NodeTIEType.|
+-----------------------------------------+-----+-------+-------+---------------------------------+
|prefixes | 2| 8.0| | Used in case of enum|
| | | | |common.TIETypeType.PrefixTIEType.|
+-----------------------------------------+-----+-------+-------+---------------------------------+
|positive_disaggregation_prefixes | 3| 8.0| | Positive prefixes (always|
| | | | | southbound).|
+-----------------------------------------+-----+-------+-------+---------------------------------+
|negative_disaggregation_prefixes | 5| 8.0| | Transitive, negative prefixes|
| | | | | (always southbound)|
+-----------------------------------------+-----+-------+-------+---------------------------------+
|external_prefixes | 6| 8.0| | Externally reimported prefixes.|
+-----------------------------------------+-----+-------+-------+---------------------------------+
|positive_external_disaggregation_prefixes| 7| 8.0| | Positive external disaggregated|
| | | | | prefixes (always southbound).|
+-----------------------------------------+-----+-------+-------+---------------------------------+
|keyvalues | 9| 8.0| | Key-Value store elements.|
+-----------------------------------------+-----+-------+-------+---------------------------------+
Table 67
10.2.33. Registry RIFT/encoding/TIEHeader
Header of a TIE.
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+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 68
+======================+=======+=========+=========+================+
| Name | Value | Min. | Max. | Description |
| | | Schema | Schema | |
| | | Version | Version | |
+======================+=======+=========+=========+================+
| tieid | 2 | 8.0 | | ID of the |
| | | | | tie. |
+----------------------+-------+---------+---------+----------------+
| seq_nr | 3 | 8.0 | | Sequence |
| | | | | number of |
| | | | | the tie. |
+----------------------+-------+---------+---------+----------------+
| origination_time | 10 | 8.0 | | Absolute |
| | | | | timestamp |
| | | | | when the |
| | | | | TIE was |
| | | | | generated. |
+----------------------+-------+---------+---------+----------------+
| origination_lifetime | 12 | 8.0 | | Original |
| | | | | lifetime |
| | | | | when the |
| | | | | TIE was |
| | | | | generated. |
+----------------------+-------+---------+---------+----------------+
Table 69
10.2.34. Registry RIFT/encoding/TIEHeaderWithLifeTime
Header of a TIE as described in TIRE/TIDE.
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+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 70
+====================+=======+=============+=========+=============+
| Name | Value | Min. Schema | Max. | Description |
| | | Version | Schema | |
| | | | Version | |
+====================+=======+=============+=========+=============+
| header | 1 | 8.0 | | |
+--------------------+-------+-------------+---------+-------------+
| remaining_lifetime | 2 | 8.0 | | Remaining |
| | | | | lifetime. |
+--------------------+-------+-------------+---------+-------------+
Table 71
10.2.35. Registry RIFT/encoding/TIEID
Unique ID of a TIE.
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 72
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+============+=======+=============+=============+=============+
| Name | Value | Min. Schema | Max. Schema | Description |
| | | Version | Version | |
+============+=======+=============+=============+=============+
| direction | 1 | 8.0 | | direction |
| | | | | of TIE |
+------------+-------+-------------+-------------+-------------+
| originator | 2 | 8.0 | | indicates |
| | | | | originator |
| | | | | of the TIE |
+------------+-------+-------------+-------------+-------------+
| tietype | 3 | 8.0 | | type of the |
| | | | | tie |
+------------+-------+-------------+-------------+-------------+
| tie_nr | 4 | 8.0 | | number of |
| | | | | the tie |
+------------+-------+-------------+-------------+-------------+
Table 73
10.2.36. Registry RIFT/encoding/TIEPacket
TIE packet
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 74
+=========+=======+=====================+=============+=============+
| Name | Value | Min. Schema | Max. Schema | Description |
| | | Version | Version | |
+=========+=======+=====================+=============+=============+
| header | 1 | 8.0 | | |
+---------+-------+---------------------+-------------+-------------+
| element | 2 | 8.0 | | |
+---------+-------+---------------------+-------------+-------------+
Table 75
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10.2.37. Registry RIFT/encoding/TIREPacket
TIRE packet
+=============================+========================+
| Schema Range | Registration Procedure |
+=============================+========================+
| Major or Minor Change per | Standards Action |
| Rules in section Appendix B | |
+-----------------------------+------------------------+
| All Other Assignments | Specification Required |
+-----------------------------+------------------------+
Table 76
+=========+=======+=====================+=============+=============+
| Name | Value | Min. Schema | Max. Schema | Description |
| | | Version | Version | |
+=========+=======+=====================+=============+=============+
| headers | 1 | 8.0 | | |
+---------+-------+---------------------+-------------+-------------+
Table 77
11. Acknowledgments
A new routing protocol in its complexity is not a product of a parent
but of a village as the author list shows already. However, many
more people provided input, fine-combed the specification based on
their experience in design, implementation or application of
protocols in IP fabrics. This section will make an inadequate
attempt in recording their contribution.
Many thanks to Naiming Shen for some of the early discussions around
the topic of using IGPs for routing in topologies related to Clos.
Russ White to be especially acknowledged for the key conversation on
epistemology that allowed to tie current asynchronous distributed
systems theory results to a modern protocol design presented in this
scope. Adrian Farrel, Joel Halpern, Jeffrey Zhang, Krzysztof
Szarkowicz, Nagendra Kumar, Melchior Aelmans, Kaushal Tank, Will
Jones, Moin Ahmed, Sandy Zhang, Donald Eastlake provided thoughtful
comments that improved the readability of the document and found good
amount of corners where the light failed to shine. Kris Price was
first to mention single router, single arm default considerations.
Jeff Tantsura helped out with some initial thoughts on BFD
interactions while Jeff Haas corrected several misconceptions about
BFD's finer points and helped to improve the security section around
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leaf considerations. Artur Makutunowicz pointed out many possible
improvements and acted as sounding board in regard to modern protocol
implementation techniques RIFT is exploring. Barak Gafni formalized
first time clearly the problem of partitioned spine and fallen leaves
on a (clean) napkin in Singapore that led to the very important part
of the specification centered around multiple ToF planes and negative
disaggregation. Igor Gashinsky and others shared many thoughts on
problems encountered in design and operation of large-scale data
center fabrics. Xu Benchong found a delicate error in the flooding
procedures and a schema datatype size mismatch.
Last but not least, Alvaro Retana, John Scudder and Andrew Alston.
As ADs they carefully reviewed and asked several necessary procedural
and technical questions, which not only improved the content but also
laid out the track towards publication.
12. Contributors
This work is a product of a list of individuals which are all to be
considered major contributors independent of the fact whether their
name made it to the limited boilerplate author's list or not.
+======================+===+==================+===+================+
+======================+===+==================+===+================+
| Tony Przygienda, Ed. | | | Alankar Sharma | | | Pascal Thubert |
+----------------------+---+------------------+---+----------------+
| Juniper | | | Individual | | | Cisco |
+----------------------+---+------------------+---+----------------+
| Bruno Rijsman | | | Jordan Head, Ed. | | | Dmitry |
| | | | | Afanasiev |
+----------------------+---+------------------+---+----------------+
| Individual | | | Juniper | | | Yandex |
+----------------------+---+------------------+---+----------------+
| Don Fedyk | | | Alia Atlas | | | John Drake |
+----------------------+---+------------------+---+----------------+
| Individual | | | Individual | | | Individual |
+----------------------+---+------------------+---+----------------+
| Ilya Vershkov | | | | | | | | |
+----------------------+---+------------------+---+----------------+
| Mellanox | | | | | | | | |
+----------------------+---+------------------+---+----------------+
Table 78: RIFT Authors
13. References
13.1. Normative References
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[EUI64] IEEE, "Guidelines for Use of Extended Unique Identifier
(EUI), Organizationally Unique Identifier (OUI), and
Company ID (CID)", IEEE EUI,
<http://standards.ieee.org/develop/regauth/tut/eui.pdf>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23,
RFC 2365, DOI 10.17487/RFC2365, July 1998,
<https://www.rfc-editor.org/info/rfc2365>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
<https://www.rfc-editor.org/info/rfc5082>.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008,
<https://www.rfc-editor.org/info/rfc5120>.
[RFC5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
Authentication", RFC 5709, DOI 10.17487/RFC5709, October
2009, <https://www.rfc-editor.org/info/rfc5709>.
[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
DOI 10.17487/RFC5881, June 2010,
<https://www.rfc-editor.org/info/rfc5881>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
[RFC7987] Ginsberg, L., Wells, P., Decraene, B., Przygienda, T., and
H. Gredler, "IS-IS Minimum Remaining Lifetime", RFC 7987,
DOI 10.17487/RFC7987, October 2016,
<https://www.rfc-editor.org/info/rfc7987>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8202] Ginsberg, L., Previdi, S., and W. Henderickx, "IS-IS
Multi-Instance", RFC 8202, DOI 10.17487/RFC8202, June
2017, <https://www.rfc-editor.org/info/rfc8202>.
[RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C.
Perkins, "Registration Extensions for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Neighbor
Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018,
<https://www.rfc-editor.org/info/rfc8505>.
[RFC9300] Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
Cabellos, Ed., "The Locator/ID Separation Protocol
(LISP)", RFC 9300, DOI 10.17487/RFC9300, October 2022,
<https://www.rfc-editor.org/info/rfc9300>.
[RFC9301] Farinacci, D., Maino, F., Fuller, V., and A. Cabellos,
Ed., "Locator/ID Separation Protocol (LISP) Control
Plane", RFC 9301, DOI 10.17487/RFC9301, October 2022,
<https://www.rfc-editor.org/info/rfc9301>.
[thrift] Apache Software Foundation, "Thrift Language
Implementation and Documentation",
<https://github.com/apache/thrift/tree/0.15.0/doc>.
13.2. Informative References
[APPLICABILITY]
Wei, Y., Zhang, Z., Afanasiev, D., Thubert, P., and T.
Przygienda, "RIFT Applicability", Work in Progress,
Internet-Draft, draft-ietf-rift-applicability-12, 25
December 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-rift-applicability-12>.
[CLOS] Yuan, X., "On Nonblocking Folded-Clos Networks in Computer
Communication Environments", IEEE International Parallel &
Distributed Processing Symposium, 2011.
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[DayOne] Aelmans, M., Vandezande, O., Rijsman, B., Head, J., Graf,
C., Alberro, L., Mali, H., and O. Steudler, "Day One:
Routing in Fat Trees (RIFT)", Juniper DayOne .
[DIJKSTRA] Dijkstra, E. W., "A Note on Two Problems in Connexion with
Graphs", Journal Numer. Math. , 1959.
[DYNAMO] De Candia et al., G., "Dynamo: amazon's highly available
key-value store", ACM SIGOPS symposium on Operating
systems principles (SOSP '07), 2007.
[EPPSTEIN] Eppstein, D., "Finding the k-Shortest Paths", 1997.
[FATTREE] Leiserson, C. E., "Fat-Trees: Universal Networks for
Hardware-Efficient Supercomputing", 1985.
[IEEEstd1588]
IEEE, "IEEE Standard for a Precision Clock Synchronization
Protocol for Networked Measurement and Control Systems",
IEEE Standard 1588,
<https://ieeexplore.ieee.org/document/4579760/>.
[IEEEstd8021AS]
IEEE, "IEEE Standard for Local and Metropolitan Area
Networks - Timing and Synchronization for Time-Sensitive
Applications in Bridged Local Area Networks",
IEEE Standard 802.1AS,
<https://ieeexplore.ieee.org/document/5741898/>.
[RFC0826] Plummer, D., "An Ethernet Address Resolution Protocol: Or
Converting Network Protocol Addresses to 48.bit Ethernet
Address for Transmission on Ethernet Hardware", STD 37,
RFC 826, DOI 10.17487/RFC0826, November 1982,
<https://www.rfc-editor.org/info/rfc826>.
[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
DOI 10.17487/RFC1982, August 1996,
<https://www.rfc-editor.org/info/rfc1982>.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<https://www.rfc-editor.org/info/rfc2131>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
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[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005,
<https://www.rfc-editor.org/info/rfc4086>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
[VAHDAT08] Al-Fares, M., Loukissas, A., and A. Vahdat, "A Scalable,
Commodity Data Center Network Architecture", SIGCOMM ,
2008.
[VFR] Giotsas, V. and S. Zhou, "Valley-free violation in
Internet routing - Analysis based on BGP Community data",
2012 IEEE International Conference on Communications
(ICC) , 2012.
Appendix A. Sequence Number Binary Arithmetic
Assuming straight two complement's subtractions on the bit-width of
the sequence numbers, the corresponding >: and =: relations are
defined as:
U_1, U_2 are 12-bits aligned unsigned version number
D_f is ( U_1 - U_2 ) interpreted as two complement signed 12-bits
D_b is ( U_2 - U_1 ) interpreted as two complement signed 12-bits
U_1 >: U_2 IIF D_f > 0 *and* D_b < 0
U_1 =: U_2 IIF D_f = 0
The >: relationship is anti-symmetric but not transitive. Observe
that this leaves >: of the numbers having maximum two complement
distance, e.g. ( 0 and 0x800 ) undefined in the 12-bits case since
D_f and D_b are both -0x7ff.
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A simple example of the relationship in case of 3-bit arithmetic
follows as table indicating D_f/D_b values and then the relationship
of U_1 to U_2:
U2 / U1 0 1 2 3 4 5 6 7
0 +/+ +/- +/- +/- -/- -/+ -/+ -/+
1 -/+ +/+ +/- +/- +/- -/- -/+ -/+
2 -/+ -/+ +/+ +/- +/- +/- -/- -/+
3 -/+ -/+ -/+ +/+ +/- +/- +/- -/-
4 -/- -/+ -/+ -/+ +/+ +/- +/- +/-
5 +/- -/- -/+ -/+ -/+ +/+ +/- +/-
6 +/- +/- -/- -/+ -/+ -/+ +/+ +/-
7 +/- +/- +/- -/- -/+ -/+ -/+ +/+
U2 / U1 0 1 2 3 4 5 6 7
0 = > > > ? < < <
1 < = > > > ? < <
2 < < = > > > ? <
3 < < < = > > > ?
4 ? < < < = > > >
5 > ? < < < = > >
6 > > ? < < < = >
7 > > > ? < < < =
Appendix B. Information Elements Schema
This section introduces the schema for information elements. The IDL
is Thrift [thrift].
On schema changes that
1. change field numbers *or*
2. add new *required* fields *or*
3. remove any fields *or*
4. change lists into sets, unions into structures *or*
5. change multiplicity of fields *or*
6. changes type or name of any field *or*
7. change data types of the type of any field *or*
8. adds, changes or removes a default value of any *existing* field
*or*
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9. removes or changes any defined constant or constant value *or*
10. changes any enumeration type except extending
`common.TIETypeType` (use of enumeration types is generally
discouraged) *or*
11. adds new TIE type to _TIETypeType_ with flooding scope different
from prefix TIE flooding scope
major version of the schema MUST increase. All other changes MUST
increase minor version within the same major.
Introducing an optional field does not cause a major version increase
even if the fields inside the structure are optional with defaults.
All signed integer as forced by Thrift [thrift] support must be cast
for internal purposes to equivalent unsigned values without
discarding the signedness bit. An implementation SHOULD try to avoid
using the signedness bit when generating values.
The schema is normative.
B.1. Backwards-Compatible Extension of Schema
The set of rules in Appendix B guarantees that every decoder can
process serialized content generated by a higher minor version of the
schema and with that the protocol can progress without a 'flag-day'.
Contrary to that, content serialized using a major version X is *not*
expected to be decodable by any implementation using decoder for a
model with a major version lower than X. Schema negotiation and
translation within RIFT is outside the scope of this document.
Additionally, based on the propagated minor version in encoded
content and added optional node capabilities new TIE types or even
de-facto mandatory fields can be introduced without progressing the
major version albeit only nodes supporting such new extensions would
decode them. Given the model is encoded at the source and never re-
encoded flooding through nodes not understanding any new extensions
will preserve the corresponding fields. However, it is important to
understand that a higher minor version of a schema does *not*
guarantee that capabilities introduced in lower minors of the same
major are supported. The _node_capabilities_ field is used to
indicate which capabilities are supported.
Specifically, the schema SHOULD add elements to _NodeCapabilities_
field future capabilities to indicate whether it will support
interpretation of schema extensions on the same major revision if
they are present. Such fields MUST be optional and have an implicit
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or explicit false default value. If a future capability changes
route selection or generates conditions that cause packet loss if
some nodes are not supporting it then a major version increment will
be however unavoidable. _NodeCapabilities_ shown in LIE MUST match
the capabilities shown in the Node TIEs, otherwise the behavior is
unspecified. A node detecting the mismatch SHOULD generate a
notification.
Alternately or additionally, new optional fields can be introduced
into e.g. _NodeTIEElement_ if a special field is chosen to indicate
via its presence that an optional feature is enabled (since
capability to support a feature does not necessarily mean that the
feature is actually configured and operational).
To support new TIE types without increasing the major version
enumeration _TIEElement_ can be extended with new optional elements
for new `common.TIETypeType` values as long the scope of the new TIE
matches the prefix TIE scope. In case it is necessary to understand
whether all nodes can parse the new TIE type a node capability MUST
be added in _NodeCapabilities_ to prevent a non-homogenous network.
B.2. common.thrift
/**
Thrift file with common definitions for RIFT
*/
namespace py common
/** @note MUST be interpreted in implementation as unsigned 64 bits.
*/
typedef i64 SystemIDType
typedef i32 IPv4Address
typedef i32 MTUSizeType
/** @note MUST be interpreted in implementation as unsigned
rolling over number */
typedef i64 SeqNrType
/** @note MUST be interpreted in implementation as unsigned */
typedef i32 LifeTimeInSecType
/** @note MUST be interpreted in implementation as unsigned */
typedef i8 LevelType
typedef i16 PacketNumberType
/** @note MUST be interpreted in implementation as unsigned */
typedef i32 PodType
/** @note MUST be interpreted in implementation as unsigned.
/** this has to be long enough to accomodate prefix */
typedef binary IPv6Address
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/** @note MUST be interpreted in implementation as unsigned */
typedef i16 UDPPortType
/** @note MUST be interpreted in implementation as unsigned */
typedef i32 TIENrType
/** @note MUST be interpreted in implementation as unsigned
This is carried in the
security envelope and must hence fit into 8 bits. */
typedef i8 VersionType
/** @note MUST be interpreted in implementation as unsigned */
typedef i16 MinorVersionType
/** @note MUST be interpreted in implementation as unsigned */
typedef i32 MetricType
/** @note MUST be interpreted in implementation as unsigned
and unstructured */
typedef i64 RouteTagType
/** @note MUST be interpreted in implementation as unstructured
label value */
typedef i32 LabelType
/** @note MUST be interpreted in implementation as unsigned */
typedef i32 BandwithInMegaBitsType
/** @note Key Value Key ID type */
typedef i32 KeyIDType
/** node local, unique identification for a link (interface/tunnel
* etc. Basically anything RIFT runs on). This is kept
* at 32 bits so it aligns with BFD [RFC5880] discriminator size.
*/
typedef i32 LinkIDType
/** @note MUST be interpreted in implementation as unsigned,
especially since we have the /128 IPv6 case. */
typedef i8 PrefixLenType
/** timestamp in seconds since the epoch */
typedef i64 TimestampInSecsType
/** security nonce.
@note MUST be interpreted in implementation as rolling
over unsigned value */
typedef i16 NonceType
/** LIE FSM holdtime type */
typedef i16 TimeIntervalInSecType
/** Transaction ID type for prefix mobility as specified by RFC6550,
value MUST be interpreted in implementation as unsigned */
typedef i8 PrefixTransactionIDType
/** Timestamp per IEEE 802.1AS, all values MUST be interpreted in
implementation as unsigned. */
struct IEEE802_1ASTimeStampType {
1: required i64 AS_sec;
2: optional i32 AS_nsec;
}
/** generic counter type */
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typedef i64 CounterType
/** Platform Interface Index type, i.e. index of interface on hardware,
can be used e.g. with RFC5837 */
typedef i32 PlatformInterfaceIndex
/** Flags indicating node configuration in case of ZTP.
*/
enum HierarchyIndications {
/** forces level to `leaf_level` and enables according procedures */
leaf_only = 0,
/** forces level to `leaf_level` and enables according procedures */
leaf_only_and_leaf_2_leaf_procedures = 1,
/** forces level to `top_of_fabric` and enables according
procedures */
top_of_fabric = 2,
}
const PacketNumberType undefined_packet_number = 0
/** used when node is configured as top of fabric in ZTP.*/
const LevelType top_of_fabric_level = 24
/** default bandwidth on a link */
const BandwithInMegaBitsType default_bandwidth = 100
/** fixed leaf level when ZTP is not used */
const LevelType leaf_level = 0
const LevelType default_level = leaf_level
const PodType default_pod = 0
const LinkIDType undefined_linkid = 0
/** invalid key for key value */
const KeyIDType invalid_key_value_key = 0
/** default distance used */
const MetricType default_distance = 1
/** any distance larger than this will be considered infinity */
const MetricType infinite_distance = 0x7FFFFFFF
/** represents invalid distance */
const MetricType invalid_distance = 0
const bool overload_default = false
const bool flood_reduction_default = true
/** default LIE FSM LIE TX internval time */
const TimeIntervalInSecType default_lie_tx_interval = 1
/** default LIE FSM holddown time */
const TimeIntervalInSecType default_lie_holdtime = 3
/** multipler for default_lie_holdtime to hold down multiple neighbors */
const i8 multiple_neighbors_lie_holdtime_multipler = 4
/** default ZTP FSM holddown time */
const TimeIntervalInSecType default_ztp_holdtime = 1
/** by default LIE levels are ZTP offers */
const bool default_not_a_ztp_offer = false
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/** by default everyone is repeating flooding */
const bool default_you_are_flood_repeater = true
/** 0 is illegal for SystemID */
const SystemIDType IllegalSystemID = 0
/** empty set of nodes */
const set<SystemIDType> empty_set_of_nodeids = {}
/** default lifetime of TIE is one week */
const LifeTimeInSecType default_lifetime = 604800
/** default lifetime when TIEs are purged is 5 minutes */
const LifeTimeInSecType purge_lifetime = 300
/** optional round down interval when TIEs are sent with security hashes
to prevent excessive computation. **/
const LifeTimeInSecType rounddown_lifetime_interval = 60
/** any `TieHeader` that has a smaller lifetime difference
than this constant is equal (if other fields equal). */
const LifeTimeInSecType lifetime_diff2ignore = 400
/** default UDP port to run LIEs on */
const UDPPortType default_lie_udp_port = 914
/** default UDP port to receive TIEs on, that can be peer specific */
const UDPPortType default_tie_udp_flood_port = 915
/** default MTU link size to use */
const MTUSizeType default_mtu_size = 1400
/** default link being BFD capable */
const bool bfd_default = true
/** type used to target nodes with key value */
typedef i64 KeyValueTargetType
/** default target for key value are all nodes. */
const KeyValueTargetType keyvaluetarget_default = 0
/** value for _all leaves_ addressing. Represented by all bits set. */
const KeyValueTargetType keyvaluetarget_all_south_leaves = -1
/** undefined nonce, equivalent to missing nonce */
const NonceType undefined_nonce = 0;
/** outer security Key ID, MUST be interpreted as in implementation
as unsigned */
typedef i8 OuterSecurityKeyID
/** security Key ID, MUST be interpreted as in implementation
as unsigned */
typedef i32 TIESecurityKeyID
/** undefined key */
const TIESecurityKeyID undefined_securitykey_id = 0;
/** Maximum delta (negative or positive) that a mirrored nonce can
deviate from local value to be considered valid. */
const i16 maximum_valid_nonce_delta = 5;
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const TimeIntervalInSecType nonce_regeneration_interval = 300;
/** Direction of TIEs. */
enum TieDirectionType {
Illegal = 0,
South = 1,
North = 2,
DirectionMaxValue = 3,
}
/** Address family type. */
enum AddressFamilyType {
Illegal = 0,
AddressFamilyMinValue = 1,
IPv4 = 2,
IPv6 = 3,
AddressFamilyMaxValue = 4,
}
/** IPv4 prefix type. */
struct IPv4PrefixType {
1: required IPv4Address address;
2: required PrefixLenType prefixlen;
}
/** IPv6 prefix type. */
struct IPv6PrefixType {
1: required IPv6Address address;
2: required PrefixLenType prefixlen;
}
/** IP address type. */
union IPAddressType {
/** Content is IPv4 */
1: optional IPv4Address ipv4address;
/** Content is IPv6 */
2: optional IPv6Address ipv6address;
}
/** Prefix advertisement.
@note: for interface
addresses the protocol can propagate the address part beyond
the subnet mask and on reachability computation that has to
be normalized. The non-significant bits can be used
for operational purposes.
*/
union IPPrefixType {
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1: optional IPv4PrefixType ipv4prefix;
2: optional IPv6PrefixType ipv6prefix;
}
/** Sequence of a prefix in case of move.
*/
struct PrefixSequenceType {
1: required IEEE802_1ASTimeStampType timestamp;
/** Transaction ID set by client in e.g. in 6LoWPAN. */
2: optional PrefixTransactionIDType transactionid;
}
/** Type of TIE.
*/
enum TIETypeType {
Illegal = 0,
TIETypeMinValue = 1,
/** first legal value */
NodeTIEType = 2,
PrefixTIEType = 3,
PositiveDisaggregationPrefixTIEType = 4,
NegativeDisaggregationPrefixTIEType = 5,
PGPrefixTIEType = 6,
KeyValueTIEType = 7,
ExternalPrefixTIEType = 8,
PositiveExternalDisaggregationPrefixTIEType = 9,
TIETypeMaxValue = 10,
}
/** RIFT route types.
@note: The only purpose of those values is to introduce an
ordering whereas an implementation can choose internally
any other values as long the ordering is preserved
*/
enum RouteType {
Illegal = 0,
RouteTypeMinValue = 1,
/** First legal value. */
/** Discard routes are most preferred */
Discard = 2,
/** Local prefixes are directly attached prefixes on the
* system such as e.g. interface routes.
*/
LocalPrefix = 3,
/** Advertised in S-TIEs */
SouthPGPPrefix = 4,
/** Advertised in N-TIEs */
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NorthPGPPrefix = 5,
/** Advertised in N-TIEs */
NorthPrefix = 6,
/** Externally imported north */
NorthExternalPrefix = 7,
/** Advertised in S-TIEs, either normal prefix or positive
disaggregation */
SouthPrefix = 8,
/** Externally imported south */
SouthExternalPrefix = 9,
/** Negative, transitive prefixes are least preferred */
NegativeSouthPrefix = 10,
RouteTypeMaxValue = 11,
}
enum KVTypes {
Experimental = 1,
WellKnown = 2,
OUI = 3,
}
B.3. encoding.thrift
/**
Thrift file for packet encodings for RIFT
*/
include "common.thrift"
namespace py encoding
/** Represents protocol encoding schema major version */
const common.VersionType protocol_major_version = 8
/** Represents protocol encoding schema minor version */
const common.MinorVersionType protocol_minor_version = 0
/** Common RIFT packet header. */
struct PacketHeader {
/** Major version of protocol. */
1: required common.VersionType major_version =
protocol_major_version;
/** Minor version of protocol. */
2: required common.MinorVersionType minor_version =
protocol_minor_version;
/** Node sending the packet, in case of LIE/TIRE/TIDE
also the originator of it. */
3: required common.SystemIDType sender;
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/** Level of the node sending the packet, required on everything
except LIEs. Lack of presence on LIEs indicates UNDEFINED_LEVEL
and is used in ZTP procedures.
*/
4: optional common.LevelType level;
}
/** Prefix community. */
struct Community {
/** Higher order bits */
1: required i32 top;
/** Lower order bits */
2: required i32 bottom;
}
/** Neighbor structure. */
struct Neighbor {
/** System ID of the originator. */
1: required common.SystemIDType originator;
/** ID of remote side of the link. */
2: required common.LinkIDType remote_id;
}
/** Capabilities the node supports. */
struct NodeCapabilities {
/** Must advertise supported minor version dialect that way. */
1: required common.MinorVersionType protocol_minor_version =
protocol_minor_version;
/** indicates that node supports flood reduction. */
2: optional bool flood_reduction =
common.flood_reduction_default;
/** indicates place in hierarchy, i.e. top-of-fabric or
leaf only (in ZTP) or support for leaf-2-leaf
procedures. */
3: optional common.HierarchyIndications hierarchy_indications;
}
/** Link capabilities. */
struct LinkCapabilities {
/** Indicates that the link is supporting BFD. */
1: optional bool bfd =
common.bfd_default;
/** Indicates whether the interface will support IPv4 forwarding. */
2: optional bool ipv4_forwarding_capable =
true;
}
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/** RIFT LIE Packet.
@note: this node's level is already included on the packet header
*/
struct LIEPacket {
/** Node or adjacency name. */
1: optional string name;
/** Local link ID. */
2: required common.LinkIDType local_id;
/** UDP port to which we can receive flooded TIEs. */
3: required common.UDPPortType flood_port =
common.default_tie_udp_flood_port;
/** Layer 3 MTU, used to discover mismatch. */
4: optional common.MTUSizeType link_mtu_size =
common.default_mtu_size;
/** Local link bandwidth on the interface. */
5: optional common.BandwithInMegaBitsType
link_bandwidth = common.default_bandwidth;
/** Reflects the neighbor once received to provide
3-way connectivity. */
6: optional Neighbor neighbor;
/** Node's PoD. */
7: optional common.PodType pod =
common.default_pod;
/** Node capabilities supported. */
10: required NodeCapabilities node_capabilities;
/** Capabilities of this link. */
11: optional LinkCapabilities link_capabilities;
/** Required holdtime of the adjacency, i.e. for how
long a period should adjacency be kept up without valid LIE reception. */
12: required common.TimeIntervalInSecType
holdtime = common.default_lie_holdtime;
/** Optional, unsolicited, downstream assigned locally significant label
value for the adjacency. */
13: optional common.LabelType label;
/** Indicates that the level on the LIE must not be used
to derive a ZTP level by the receiving node. */
21: optional bool not_a_ztp_offer =
common.default_not_a_ztp_offer;
/** Indicates to northbound neighbor that it should
be reflooding TIEs received from this node to achieve flood
reduction and balancing for northbound flooding. */
22: optional bool you_are_flood_repeater =
common.default_you_are_flood_repeater;
/** Indicates to neighbor to flood node TIEs only and slow down
all other TIEs. Ignored when received from southbound neighbor. */
23: optional bool you_are_sending_too_quickly =
false;
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/** Instance name in case multiple RIFT instances running on same
interface. */
24: optional string instance_name;
/** It provides the optional ID of the Fabric configured. This MUST match the information advertised
on the node element. */
35: optional common.FabricIDType fabric_id = common.default_fabric_id;
}
/** LinkID pair describes one of parallel links between two nodes. */
struct LinkIDPair {
/** Node-wide unique value for the local link. */
1: required common.LinkIDType local_id;
/** Received remote link ID for this link. */
2: required common.LinkIDType remote_id;
/** Describes the local interface index of the link. */
10: optional common.PlatformInterfaceIndex platform_interface_index;
/** Describes the local interface name. */
11: optional string platform_interface_name;
/** Indicates whether the link is secured, i.e. protected by
outer key, absence of this element means no indication,
undefined outer key means not secured. */
12: optional common.OuterSecurityKeyID
trusted_outer_security_key;
/** Indicates whether the link is protected by established
BFD session. */
13: optional bool bfd_up;
/** Optional indication which address families are up on the
interface */
14: optional set<common.AddressFamilyType>
address_families;
}
/** Unique ID of a TIE. */
struct TIEID {
/** direction of TIE */
1: required common.TieDirectionType direction;
/** indicates originator of the TIE */
2: required common.SystemIDType originator;
/** type of the tie */
3: required common.TIETypeType tietype;
/** number of the tie */
4: required common.TIENrType tie_nr;
}
/** Header of a TIE. */
struct TIEHeader {
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/** ID of the tie. */
2: required TIEID tieid;
/** Sequence number of the tie. */
3: required common.SeqNrType seq_nr;
/** Absolute timestamp when the TIE was generated. */
10: optional common.IEEE802_1ASTimeStampType origination_time;
/** Original lifetime when the TIE was generated. */
12: optional common.LifeTimeInSecType origination_lifetime;
}
/** Header of a TIE as described in TIRE/TIDE.
*/
struct TIEHeaderWithLifeTime {
1: required TIEHeader header;
/** Remaining lifetime. */
2: required common.LifeTimeInSecType remaining_lifetime;
}
/** TIDE with *sorted* TIE headers. */
struct TIDEPacket {
/** First TIE header in the tide packet. */
1: required TIEID start_range;
/** Last TIE header in the tide packet. */
2: required TIEID end_range;
/** _Sorted_ list of headers. */
3: required list<TIEHeaderWithLifeTime>
headers;
}
/** TIRE packet */
struct TIREPacket {
1: required set<TIEHeaderWithLifeTime>
headers;
}
/** neighbor of a node */
struct NodeNeighborsTIEElement {
/** level of neighbor */
1: required common.LevelType level;
/** Cost to neighbor. Ignore anything larger than `infinite_distance` and `invalid_distance` */
3: optional common.MetricType cost
= common.default_distance;
/** can carry description of multiple parallel links in a TIE */
4: optional set<LinkIDPair>
link_ids;
/** total bandwith to neighbor as sum of all parallel links */
5: optional common.BandwithInMegaBitsType
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bandwidth = common.default_bandwidth;
}
/** Indication flags of the node. */
struct NodeFlags {
/** Indicates that node is in overload, do not transit traffic
through it. */
1: optional bool overload = common.overload_default;
}
/** Description of a node. */
struct NodeTIEElement {
/** Level of the node. */
1: required common.LevelType level;
/** Node's neighbors. Multiple node TIEs can carry disjoint sets of neighbors. */
2: required map<common.SystemIDType,
NodeNeighborsTIEElement> neighbors;
/** Capabilities of the node. */
3: required NodeCapabilities capabilities;
/** Flags of the node. */
4: optional NodeFlags flags;
/** Optional node name for easier operations. */
5: optional string name;
/** PoD to which the node belongs. */
6: optional common.PodType pod;
/** optional startup time of the node */
7: optional common.TimestampInSecsType startup_time;
/** If any local links are miscabled, this indication is flooded. */
10: optional set<common.LinkIDType>
miscabled_links;
/** ToFs in the same plane. Only carried by ToF. Multiple Node TIEs can carry disjoint sets of ToFs
which MUST be joined to form a single set. */
12: optional set<common.SystemIDType>
same_plane_tofs;
/** It provides the optional ID of the Fabric configured */
20: optional common.FabricIDType fabric_id = common.default_fabric_id;
}
/** Attributes of a prefix. */
struct PrefixAttributes {
/** Distance of the prefix. */
2: required common.MetricType metric
= common.default_distance;
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/** Generic unordered set of route tags, can be redistributed
to other protocols or use within the context of real time
analytics. */
3: optional set<common.RouteTagType>
tags;
/** Monotonic clock for mobile addresses. */
4: optional common.PrefixSequenceType monotonic_clock;
/** Indicates if the prefix is a node loopback. */
6: optional bool loopback = false;
/** Indicates that the prefix is directly attached. */
7: optional bool directly_attached = true;
/** link to which the address belongs to. */
10: optional common.LinkIDType from_link;
/** Optional, per prefix significant label. */
12: optional common.LabelType label;
}
/** TIE carrying prefixes */
struct PrefixTIEElement {
/** Prefixes with the associated attributes. */
1: required map<common.IPPrefixType, PrefixAttributes> prefixes;
}
/** Defines the targeted nodes and the value carried. */
struct KeyValueTIEElementContent {
1: optional common.KeyValueTargetType targets = common.keyvaluetarget_default;
2: optional binary value;
}
/** Generic key value pairs. */
struct KeyValueTIEElement {
1: required map<common.KeyIDType, KeyValueTIEElementContent> keyvalues;
}
/** Single element in a TIE. */
union TIEElement {
/** Used in case of enum common.TIETypeType.NodeTIEType. */
1: optional NodeTIEElement node;
/** Used in case of enum common.TIETypeType.PrefixTIEType. */
2: optional PrefixTIEElement prefixes;
/** Positive prefixes (always southbound). */
3: optional PrefixTIEElement positive_disaggregation_prefixes;
/** Transitive, negative prefixes (always southbound) */
5: optional PrefixTIEElement negative_disaggregation_prefixes;
/** Externally reimported prefixes. */
6: optional PrefixTIEElement external_prefixes;
/** Positive external disaggregated prefixes (always southbound). */
7: optional PrefixTIEElement
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positive_external_disaggregation_prefixes;
/** Key-Value store elements. */
9: optional KeyValueTIEElement keyvalues;
}
/** TIE packet */
struct TIEPacket {
1: required TIEHeader header;
2: required TIEElement element;
}
/** Content of a RIFT packet. */
union PacketContent {
1: optional LIEPacket lie;
2: optional TIDEPacket tide;
3: optional TIREPacket tire;
4: optional TIEPacket tie;
}
/** RIFT packet structure. */
struct ProtocolPacket {
1: required PacketHeader header;
2: required PacketContent content;
}
Authors' Addresses
Tony Przygienda (editor)
Juniper Networks
1137 Innovation Way
Sunnyvale, CA 94089
United States of America
Email: prz@juniper.net
Jordan Head (editor)
Juniper Networks
1137 Innovation Way
Sunnyvale, CA 94089
United States of America
Email: jhead@juniper.net
Pascal Thubert
Cisco Systems, Inc
Building D
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45 Allee des Ormes - BP1200
06254 MOUGINS - Sophia Antipolis
France
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
Bruno Rijsman
Individual
Email: brunorijsman@gmail.com
Dmitry Afanasiev
Yandex
Email: fl0w@yandex-team.ru
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