Internet DRAFT - draft-shen-isis-spine-leaf-ext
draft-shen-isis-spine-leaf-ext
Networking Working Group N. Shen
Internet-Draft L. Ginsberg
Intended status: Standards Track Cisco Systems
Expires: April 19, 2019 S. Thyamagundalu
October 16, 2018
IS-IS Routing for Spine-Leaf Topology
draft-shen-isis-spine-leaf-ext-07
Abstract
This document describes a mechanism for routers and switches in a
Spine-Leaf type topology to have non-reciprocal Intermediate System
to Intermediate System (IS-IS) routing relationships between the
leafs and spines. The leaf nodes do not need to have the topology
information of other nodes and exact prefixes in the network. This
extension also has application in the Internet of Things (IoT).
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 19, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Motivations . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Spine-Leaf (SL) Extension . . . . . . . . . . . . . . . . . . 4
3.1. Topology Examples . . . . . . . . . . . . . . . . . . . . 4
3.2. Applicability Statement . . . . . . . . . . . . . . . . . 5
3.3. Spine-Leaf TLV . . . . . . . . . . . . . . . . . . . . . 6
3.3.1. Spine-Leaf Sub-TLVs . . . . . . . . . . . . . . . . . 7
3.3.1.1. Leaf-Set Sub-TLV . . . . . . . . . . . . . . . . 7
3.3.1.2. Info-Req Sub-TLV . . . . . . . . . . . . . . . . 8
3.3.2. Advertising IPv4/IPv6 Reachability . . . . . . . . . 8
3.3.3. Advertising Connection to RF-Leaf Node . . . . . . . 8
3.4. Mechanism . . . . . . . . . . . . . . . . . . . . . . . . 8
3.4.1. Pure CLOS Topology . . . . . . . . . . . . . . . . . 10
3.5. Implementation and Operation . . . . . . . . . . . . . . 11
3.5.1. CSNP PDU . . . . . . . . . . . . . . . . . . . . . . 11
3.5.2. Overload Bit . . . . . . . . . . . . . . . . . . . . 11
3.5.3. Spine Node Hostname . . . . . . . . . . . . . . . . . 11
3.5.4. IS-IS Reverse Metric . . . . . . . . . . . . . . . . 11
3.5.5. Spine-Leaf Traffic Engineering . . . . . . . . . . . 12
3.5.6. Other End-to-End Services . . . . . . . . . . . . . . 12
3.5.7. Address Family and Topology . . . . . . . . . . . . . 12
3.5.8. Migration . . . . . . . . . . . . . . . . . . . . . . 13
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
7. Document Change Log . . . . . . . . . . . . . . . . . . . . . 14
7.1. Changes to draft-shen-isis-spine-leaf-ext-05.txt . . . . 14
7.2. Changes to draft-shen-isis-spine-leaf-ext-04.txt . . . . 14
7.3. Changes to draft-shen-isis-spine-leaf-ext-03.txt . . . . 14
7.4. Changes to draft-shen-isis-spine-leaf-ext-02.txt . . . . 14
7.5. Changes to draft-shen-isis-spine-leaf-ext-01.txt . . . . 15
7.6. Changes to draft-shen-isis-spine-leaf-ext-00.txt . . . . 15
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Normative References . . . . . . . . . . . . . . . . . . 15
8.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
The IS-IS routing protocol defined by [ISO10589] has been widely
deployed in provider networks, data centers and enterprise campus
environments. In the data center and enterprise switching networks,
a Spine-Leaf topology is commonly used. This document describes a
mechanism where IS-IS routing can be optimized for a Spine-Leaf
topology.
In a Spine-Leaf topology, normally a leaf node connects to a number
of spine nodes. Data traffic going from one leaf node to another
leaf node needs to pass through one of the spine nodes. Also, the
decision to choose one of the spine nodes is usually part of equal
cost multi-path (ECMP) load sharing. The spine nodes can be
considered as gateway devices to reach destinations on other leaf
nodes. In this type of topology, the spine nodes have to know the
topology and routing information of the entire network, but the leaf
nodes only need to know how to reach the gateway devices to which are
the spine nodes they are uplinked.
This document describes the IS-IS Spine-Leaf extension that allows
the spine nodes to have all the topology and routing information,
while keeping the leaf nodes free of topology information other than
the default gateway routing information. The leaf nodes do not even
need to run a Shortest Path First (SPF) calculation since they have
no topology information.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Motivations
o The leaf nodes in a Spine-Leaf topology do not require complete
topology and routing information of the entire domain since their
forwarding decision is to use ECMP with spine nodes as default
gateways
o The spine nodes in a Spine-Leaf topology are richly connected to
leaf nodes, which introduces significant flooding duplication if
they flood all Link State PDUs (LSPs) to all the leaf nodes. It
saves both spine and leaf nodes' CPU and link bandwidth resources
if flooding is blocked to leaf nodes. For small Top of the Rack
(ToR) leaf switches in data centers, it is meaningful to prevent
full topology routing information and massive database flooding
through those devices.
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o When a spine node advertises a topology change, every leaf node
connected to it will flood the update to all the other spine
nodes, and those spine nodes will further flood them to all the
leaf nodes, causing a O(n^2) flooding storm which is largely
redundant.
o Similar to some of the overlay technologies which are popular in
data centers, the edge devices (leaf nodes) may not need to
contain all the routing and forwarding information on the device's
control and forwarding planes. "Conversational Learning" can be
utilized to get the specific routing and forwarding information in
the case of pure CLOS topology and in the events of link and node
down.
o Small devices and appliances of Internet of Things (IoT) can be
considered as leafs in the routing topology sense. They have CPU
and memory constrains in design, and those IoT devices do not have
to know the exact network topology and prefixes as long as there
are ways to reach the cloud servers or other devices.
3. Spine-Leaf (SL) Extension
3.1. Topology Examples
+--------+ +--------+ +--------+
| | | | | |
| Spine1 +----+ Spine2 +- ......... -+ SpineN |
| | | | | |
+-+-+-+-++ ++-+-+-+-+ +-+-+-+-++
+------+ | | | | | | | | | | |
| +-----|-|-|------+ | | | | | | |
| | +--|-|-|--------+-|-|-----------------+ | | |
| | | | | | +---+ | | | | |
| | | | | | | +--|-|-------------------+ | |
| | | | | | | | | | +------+ +----+
| | | | | | | | | +--------------|----------+ |
| | | | | | | | +-------------+ | | |
| | | | | +----|--|----------------|--|--------+ | |
| | | | +------|--|--------------+ | | | | |
| | | +------+ | | | | | | | |
++--+--++ +-+-+--++ ++-+--+-+ ++-+--+-+
| Leaf1 | | Leaf2 | ........ | LeafX | | LeafY |
+-------+ +-------+ +-------+ +-------+
Figure 1: A Spine-Leaf Topology
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+---------+ +--------+
| Spine1 | | Spine2 |
+-+-+-+-+-+ +-+-+-+-++
| | | | | | | |
| | | +-----------------|-|-|-|-+
| | +------------+ | | | | |
+--------+ +-+ | | | | | |
| +----------------------------+ | | | |
| | | +------------------+ | +----+
| | | | | +-------+ | |
| | | | | | | |
+-+---+-+ +--+--+-+ +-+--+--+ +--+--+-+
| Leaf1 | | Leaf2 | | Leaf3 | | Leaf4 |
+-------+ +-------+ +-------+ +-------+
Figure 2: A CLOS Topology
3.2. Applicability Statement
This extension assumes the network is a Spine-Leaf topology, and it
should not be applied in an arbitrary network setup. The spine nodes
can be viewed as the aggregation layer of the network, and the leaf
nodes as the access layer of the network. The leaf nodes use a load
sharing algorithm with spine nodes as nexthops in routing and
forwarding.
This extension works when the spine nodes are inter-connected, and it
works with a pure CLOS or Fat Tree topology based network where the
spines are NOT horizontally interconnected.
Although the example diagram in Figure 1 shows a fully meshed Spine-
Leaf topology, this extension also works in the case where they are
partially meshed. For instance, leaf1 through leaf10 may be fully
meshed with spine1 through spine5 while leaf11 through leaf20 is
fully meshed with spine4 through spine8, and all the spines are
inter-connected in a redundant fashion.
This extension can also work in multi-level spine-leaf topology. The
lower level spine node can be a 'leaf' node to the upper level spine
node. A spine-leaf 'Tier' can be exchanged with IS-IS hello packets
to allow tier X to be connected with tier X+1 using this extension.
Normally tier-0 will be the TOR routers and switches if provisioned.
This extension also works with normal IS-IS routing in a topology
with more than two layers of spine and leaf. For instance, in
example diagrams Figure 1 and Figure 2, there can be another Core
layer of routers/switches on top of the aggregation layer. From an
IS-IS routing point of view, the Core nodes are not affected by this
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extension and will have the complete topology and routing information
just like the spine nodes. To make the network even more scalable,
the Core layer can operate as a level-2 IS-IS sub-domain while the
Spine and Leaf layers operate as stays at the level-1 IS-IS domain.
This extension assumes the link between the spine and leaf nodes are
point-to-point, or point-to-point over LAN [RFC5309]. The links
connecting among the spine nodes or the links between the leaf nodes
can be any type.
3.3. Spine-Leaf TLV
This extension introduces a new TLV, the Spine-Leaf TLV, which may be
advertised in IS-IS Hello (IIH) PDUs, LSPs, or in Circuit Scoped Link
State PDUs (CS-LSP) [RFC7356]. It is used by both spine and leaf
nodes in this Spine-Leaf mechanism.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | SL Flag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .. Optional Sub-TLVs
+-+-+-+-+-+-+-+-+-....
The fields of this TLV are defined as follows:
Type: 1 octet Suggested value 150 (to be assigned by IANA)
Length: 1 octet (2 + length of sub-TLVs).
SL Flags: 16 bits
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tier | Reserved |T|R|L|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Tier: A value from 0 to 15. It represents the spine-leaf
tier level. The value 15 is reserved to indicate the
tier level is unknown. This value is only valid when
the 'T' bit (see below) is set. If the 'T' bit is
clear, this value MUST be set to zero on transmission,
and it MUST be ignored on receipt.
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L bit (0x01): Only leaf node sets this bit. If the L bit is
set in the SL flag, the node indicates it is in 'Leaf-
Mode'.
R bit (0x02): Only Spine node sets this bit. If the R bit is
set, the node indicates to the leaf neighbor that it
can be used as the default route gateway.
T bit (0x04): If set, the value in the "Tier" field (see
above) is valid.
Optional Sub-TLV: Not defined in this document, for future
extension
sub-TLVs MAY be included when the TLV is in a CS-LSP.
sub-TLVs MUST NOT be included when the TLV is in an IIH
3.3.1. Spine-Leaf Sub-TLVs
If the data center topology is a pure CLOS or Fat Tree, there are no
link connections among the spine nodes. If we also assume there is
not another Core layer on top of the aggregation layer, then the
traffic from one leaf node to another may have a problem if there is
a link outage between a spine node and a leaf node. For instance, in
the diagram of Figure 2, if Leaf1 sends data traffic to Leaf3 through
Spine1 node, and the Spine1-Leaf3 link is down, the data traffic will
be dropped on the Spine1 node.
To address this issue spine and leaf nodes may send/request specific
reachability information via the sub-TLVs defined below.
Two Spine-Leaf sub-TLVs are defined. The Leaf-Set sub-TLV and the
Info-Req sub-TLV.
3.3.1.1. Leaf-Set Sub-TLV
This sub-TLV is used by spine nodes to optionally advertise Leaf
neighbors to other Leaf nodes. The fields of this sub-TLV are
defined as follows:
Type: 1 octet Suggested value 1 (to be assigned by IANA)
Length: 1 octet MUST be a multiple of 6 octets.
Leaf-Set: A list of IS-IS System-ID of the leaf node neighbors of
this spine node.
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3.3.1.2. Info-Req Sub-TLV
This sub-TLV is used by leaf nodes to request the advertisement of
more specific prefix information from a selected spine node. The
list of leaf nodes in this sub-TLV reflects the current set of leaf-
nodes for which not all spine node neighbors have indicated the
presence of connectivity in the Leaf-Set sub-TLV (See
Section 3.3.1.1). The fields of this sub-TLV are defined as follows:
Type: 1 octet Suggested value 2 (to be assigned by IANA)
Length: 1 octet. It MUST be a multiple of 6 octets.
Info-Req: List of IS-IS System-IDs of leaf nodes for which
connectivity information is being requested.
3.3.2. Advertising IPv4/IPv6 Reachability
In cases where connectivity between a leaf node and a spine node is
down, the leaf node MAY request reachability information from a spine
node as described in Section 3.3.1.2. The spine node utilizes TLVs
135 [RFC5305] and TLVs 236 [RFC5308] to advertise this information.
These TLVs MAY be included either in IIHs or CS-LSPs [RFC7356] sent
from the spine to the requesting leaf node. Sending such information
in IIHs has limited scale - all reachability information MUST fit
within a single IIH. It is therefore recommended that CS-LSPs be
used.
3.3.3. Advertising Connection to RF-Leaf Node
For links between Spine and Leaf Nodes on which the Spine Node has
set the R-bit and the Leaf node has set the L-bit in their respective
Spine-Leaf TLVs, spine nodes may advertise the link with a bit in the
"link-attribute" sub-TLV [RFC5029] to express this link is not used
for LSP flooding. This information can be used by nodes computing a
flooding topology e.g., [DYNAMIC-FLOODING], to exclude the RF-Leaf
nodes from the computed flooding topology.
3.4. Mechanism
Leaf nodes in a spine-leaf application using this extension are
provisioned with two attributes:
1)Tier level of 0. This indicates the node is a Leaf Node. The
value 0 is advertised in the Tier field of Spine-Leaf TLV defined
above.
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2)Flooding reduction enabled/disabled. If flooding reduction is
enabled the L-bit is set to one in the Spine-Leaf TLV defined above
A spine node does not need explicit configuration. Spine nodes can
dynamically discover their tier level by computing the number of hops
to a leaf node. Until a spine node determines its tier level it MUST
advertise level 15 (unknown tier level) in the Spine-Leaf TLV defined
above. Each tier level can also be statically provisioned on the
node.
When a spine node receives an IIH which includes the Spine-Leaf TLV
with Tier level 0 and 'L' bit set, it labels the point-to-point
interface and adjacency to be a 'Reduced Flooding Leaf-Peer (RF-
Leaf)'. IIHs sent by a spine node on a link to an RF-Leaf include
the Spine-Leaf TLV with the 'R' bit set in the flags field. The 'R'
bit indicates to the RF-Leaf neighbor that the spine node can be used
as a default routing nexthop.
There is no change to the IS-IS adjacency bring-up mechanism for
Spine-Leaf peers.
A spine node blocks LSP flooding to RF-Leaf adjacencies, except for
the LSP PDUs in which the IS-IS System-ID matches the System-ID of
the RF-Leaf neighbor. This exception is needed since when the leaf
node reboots, the spine node needs to forward to the leaf node non-
purged LSPs from the RF-Leaf's previous incarnation.
Leaf nodes will perform IS-IS LSP flooding as normal over all of its
IS-IS adjacencies, but in the case of RF-Leafs only self-originated
LSPs will exist in its LSP database.
Spine nodes will receive all the LSP PDUs in the network, including
all the spine nodes and leaf nodes. It will perform Shortest Path
First (SPF) as a normal IS-IS node does. There is no change to the
route calculation and forwarding on the spine nodes.
The LSPs of a node only floods north bound towards the upper layer
spine nodes. The default route is generated with loadsharing also
towards the upper layer spine nodes.
RF-Leaf nodes do not have any LSP in the network except for its own.
Therefore there is no need to perform SPF calculation on the RF-Leaf
node. It only needs to download the default route with the nexthops
of those Spine Neighbors which have the 'R' bit set in the Spine-Leaf
TLV in IIH PDUs. IS-IS can perform equal cost or unequal cost load
sharing while using the spine nodes as nexthops. The aggregated
metric of the outbound interface and the 'Reverse Metric'
[REVERSE-METRIC] can be used for this purpose.
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3.4.1. Pure CLOS Topology
In a data center where the topology is pure CLOS or Fat Tree, there
is no interconnection among the spine nodes, and there is not another
Core layer above the aggregation layer with reachability to the leaf
nodes. When flooding reduction to RF-Leafs is in use, if the link
between a spine and a leaf goes down, there is then a possibility of
black holing the data traffic in the network.
As in the diagram Figure 2, if the link Spine1-Leaf3 goes down, there
needs to be a way for Leaf1, Leaf2 and Leaf4 to avoid the Spine1 if
the destination of data traffic is to Leaf3 node.
In the above example, the Spine1 and Spine2 are provisioned to
advertise the Leaf-Set sub-TLV of the Spine-Leaf TLV. Originally
both Spines will advertise Leaf1 through Leaf4 as their Leaf-Set.
When the Spine1-Leaf3 link is down, Spine1 will only have Leaf1,
Leaf2 and Leaf4 in its Leaf-Set. This allows the other leaf nodes to
know that Spine1 has lost connectivity to the leaf node of Leaf3.
Each RF-Leaf node can select another spine node to request for some
prefix information associated with the lost leaf node. In this
diagram of Figure 2, there are only two spine nodes (Spine-Leaf
topology can have more than two spine nodes in general). Each RF-
Leaf node can independently select a spine node for the leaf
information. The RF-Leaf nodes will include the Info-Req sub-TLV in
the Spine-Leaf TLV in hellos sent to the selected spine node, Spine2
in this case.
The spine node, upon receiving the request from one or more leaf
nodes, will find the IPv6/IPv4 prefixes advertised by the leaf nodes
listed in the Info-Req sub-TLV. The spine node will use the
mechanism defined in Section 3.3.2 to advertise these prefixes to the
RF-Leaf node. For instance, it will include the IPv4 loopback prefix
of leaf3 based on the policy configured or administrative tag
attached to the prefixes. When the leaf nodes receive the more
specific prefixes, they will install the advertised prefixes towards
the other spine nodes (Spine2 in this example).
For instance in the data center overlay scenario, when any IP
destination or MAC destination uses the leaf3's loopback as the
tunnel nexthop, the overlay tunnel from leaf nodes will only select
Spine2 as the gateway to reach leaf3 as long as the Spine1-Leaf3 link
is still down.
In cases where multiple links or nodes fail at the same time, the RF-
leaf node may need to send the Info-Req to multiple upper layer spine
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nodes in order to obtain reachability information for all the
partially connected nodes.
This negative routing is more useful between tier 0 and tier 1 spine-
leaf levels in a multi-level spine-leaf topology when the reduced
flooding extension is in use. Nodes in tiers 1 or greater may have
much richer topology information and alternative paths.
3.5. Implementation and Operation
3.5.1. CSNP PDU
In Spine-Leaf extension, Complete Sequence Number PDU (CSNP) does not
need to be transmitted over the Spine-Leaf link to an RF-Leaf. Some
IS-IS implementations send periodic CSNPs after the initial adjacency
bring-up over a point-to-point interface. There is no need for this
optimization here since the RF-Leaf does not need to receive any
other LSPs from the network, and the only LSPs transmitted across the
Spine-Leaf link is the leaf node LSP.
Also in the graceful restart case[RFC5306], for the same reason,
there is no need to send the CSNPs over the Spine-Leaf interface to
an RF-Leaf. Spine nodes only need to set the SRMflag on the LSPs
belonging to the RF-Leaf.
3.5.2. Overload Bit
The leaf node SHOULD set the 'overload' bit on its LSP PDU, since if
the spine nodes were to forward traffic not meant for the local node,
the leaf node does not have the topology information to prevent a
routing/forwarding loop.
3.5.3. Spine Node Hostname
This extension creates a non-reciprocal relationship between the
spine node and leaf node. The spine node will receive leaf's LSP and
will know the leaf's hostname, but the leaf does not have spine's
LSP. This extension allows the Dynamic Hostname TLV [RFC5301] to be
optionally included in spine's IIH PDU when sending to a 'Leaf-Peer'.
This is useful in troubleshooting cases.
3.5.4. IS-IS Reverse Metric
This metric is part of the aggregated metric for leaf's default route
installation with load sharing among the spine nodes. When a spine
node is in 'overload' condition, it should use the IS-IS Reverse
Metric TLV in IIH [REVERSE-METRIC] to set this metric to maximum to
discourage the leaf using it as part of the loadsharing.
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In some cases, certain spine nodes may have less bandwidth in link
provisioning or in real-time condition, and it can use this metric to
signal to the leaf nodes dynamically.
In other cases, such as when the spine node loses a link to a
particular leaf node, although it can redirect the traffic to other
spine nodes to reach that destination leaf node, but it MAY want to
increase this metric value if the inter-spine connection becomes over
utilized, or the latency becomes an issue.
In the leaf-leaf link as a backup gateway use case, the 'Reverse
Metric' SHOULD always be set to very high value.
3.5.5. Spine-Leaf Traffic Engineering
Besides using the IS-IS Reverse Metric by the spine nodes to affect
the traffic pattern for leaf default gateway towards multiple spine
nodes, the IPv6/IPv4 Info-Advertise sub-TLVs can be selectively used
by traffic engineering controllers to move data traffic around the
data center fabric to alleviate congestion and to reduce the latency
of a certain class of traffic pairs. By injecting more specific leaf
node prefixes, it will allow the spine nodes to attract more traffic
on some underutilized links.
3.5.6. Other End-to-End Services
Losing the topology information will have an impact on some of the
end-to-end network services, for instance, MPLS TE or end-to-end
segment routing. Some other mechanisms such as those described in
PCE [RFC4655] based solution may be used. In this Spine-Leaf
extension, the role of the leaf node is not too much different from
the multi-level IS-IS routing while the level-1 IS-IS nodes only have
the default route information towards the node which has the Attach
Bit (ATT) set, and the level-2 backbone does not have any topology
information of the level-1 areas. The exact mechanism to enable
certain end-to-end network services in Spine-Leaf network is outside
the scope of this document.
3.5.7. Address Family and Topology
IPv6 Address families[RFC5308], Multi-Topology (MT)[RFC5120] and
Multi-Instance (MI)[RFC8202] information is carried over the IIH PDU.
Since the goal is to simplify the operation of IS-IS network, for the
simplicity of this extension, the Spine-Leaf mechanism is applied the
same way to all the address families, MTs and MIs.
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3.5.8. Migration
For this extension to be deployed in existing networks, a simple
migration scheme is needed. To support any leaf node in the network,
all the involved spine nodes have to be upgraded first. So the first
step is to migrate all the involved spine nodes to support this
extension, then the leaf nodes can be enabled with 'Leaf-Mode' one by
one. No flag day is needed for the extension migration.
4. IANA Considerations
A new TLV codepoint is defined in this document and needs to be
assigned by IANA from the "IS-IS TLV Codepoints" registry. It is
referred to as the Spine-Leaf TLV and the suggested value is 150.
This TLV is only to be optionally inserted either in the IIH PDU or
in the Circuit Flooding Scoped LSP PDU. IANA is also requested to
maintain the SL-flag bit values in this TLV, and 0x01, 0x02 and 0x04
bits are defined in this document.
Value Name IIH LSP SNP Purge CS-LSP
----- --------------------- --- --- --- ----- -------
150 Spine-Leaf y y n n y
This extension also proposes to have the Dynamic Hostname TLV,
already assigned as code 137, to be allowed in IIH PDU.
Value Name IIH LSP SNP Purge
----- --------------------- --- --- --- -----
137 Dynamic Name y y n y
Two new sub-TLVs are defined in this document and needs to be added
assigned by IANA from the "IS-IS TLV Codepoints". They are referred
to in this document as the Leaf-Set sub-TLV and the Info-Req sub-TLV.
It is suggested to have the values 1 and 2 respectively.
This document also requests that IANA allocate from the registry of
link-attribute bit values for sub-TLV 19 of TLV 22 (Extended IS
reachability TLV). This new bit is referred to as the "Connect to
RF-Leaf Node" bit.
Value Name Reference
----- ----- ----------
0x3 Connect to RF-Leaf Node This document
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5. Security Considerations
Security concerns for IS-IS are addressed in [ISO10589], [RFC5304],
[RFC5310], and [RFC7602]. This extension does not raise additional
security issues.
6. Acknowledgments
The authors would like to thank Tony Przygienda for his discussion
and contributions. The authors also would like to thank Acee Lindem,
Russ White and Christian Hopps for their review and comments of this
document.
7. Document Change Log
7.1. Changes to draft-shen-isis-spine-leaf-ext-05.txt
o Submitted January 2018.
o Just a refresh.
7.2. Changes to draft-shen-isis-spine-leaf-ext-04.txt
o Submitted June 2017.
o Added the Tier level information to handle the multi-level spine-
leaf topology using this extension.
7.3. Changes to draft-shen-isis-spine-leaf-ext-03.txt
o Submitted March 2017.
o Added the Spine-Leaf sub-TLVs to handle the case of data center
pure CLOS topology and mechanism.
o Added the Spine-Leaf TLV and sub-TLVs can be optionally inserted
in either IIH PDU or CS-LSP PDU.
o Allow use of prefix Reachability TLVs 135 and 236 in IIHs/CS-LSPs
sent from spine to leaf.
7.4. Changes to draft-shen-isis-spine-leaf-ext-02.txt
o Submitted October 2016.
o Removed the 'Default Route Metric' field in the Spine-Leaf TLV and
changed to using the IS-IS Reverse Metric in IIH.
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7.5. Changes to draft-shen-isis-spine-leaf-ext-01.txt
o Submitted April 2016.
o No change. Refresh the draft version.
7.6. Changes to draft-shen-isis-spine-leaf-ext-00.txt
o Initial version of the draft is published in November 2015.
8. References
8.1. Normative References
[ISO10589]
ISO "International Organization for Standardization",
"Intermediate system to Intermediate system intra-domain
routeing information exchange protocol for use in
conjunction with the protocol for providing the
connectionless-mode Network Service (ISO 8473), ISO/IEC
10589:2002, Second Edition.", Nov 2002.
[REVERSE-METRIC]
Shen, N., Amante, S., and M. Abrahamsson, "IS-IS Routing
with Reverse Metric", draft-ietf-isis-reverse-metric-07
(work in progress), 2017.
[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>.
[RFC5029] Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link
Attribute Sub-TLV", RFC 5029, DOI 10.17487/RFC5029,
September 2007, <https://www.rfc-editor.org/info/rfc5029>.
[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>.
[RFC5301] McPherson, D. and N. Shen, "Dynamic Hostname Exchange
Mechanism for IS-IS", RFC 5301, DOI 10.17487/RFC5301,
October 2008, <https://www.rfc-editor.org/info/rfc5301>.
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Internet-Draft IS-IS SL Extension October 2018
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, DOI 10.17487/RFC5304, October
2008, <https://www.rfc-editor.org/info/rfc5304>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC5306] Shand, M. and L. Ginsberg, "Restart Signaling for IS-IS",
RFC 5306, DOI 10.17487/RFC5306, October 2008,
<https://www.rfc-editor.org/info/rfc5306>.
[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
DOI 10.17487/RFC5308, October 2008, <https://www.rfc-
editor.org/info/rfc5308>.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, DOI 10.17487/RFC5310, February
2009, <https://www.rfc-editor.org/info/rfc5310>.
[RFC7356] Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
Scope Link State PDUs (LSPs)", RFC 7356,
DOI 10.17487/RFC7356, September 2014, <https://www.rfc-
editor.org/info/rfc7356>.
[RFC7602] Chunduri, U., Lu, W., Tian, A., and N. Shen, "IS-IS
Extended Sequence Number TLV", RFC 7602,
DOI 10.17487/RFC7602, July 2015, <https://www.rfc-
editor.org/info/rfc7602>.
[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>.
8.2. Informative References
[DYNAMIC-FLOODING]
Li, T., "Dynamic Flooding on Dense Graphs", draft-li-
dynamic-flooding (work in progress), 2018.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006, <https://www.rfc-
editor.org/info/rfc4655>.
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[RFC5309] Shen, N., Ed. and A. Zinin, Ed., "Point-to-Point Operation
over LAN in Link State Routing Protocols", RFC 5309,
DOI 10.17487/RFC5309, October 2008, <https://www.rfc-
editor.org/info/rfc5309>.
Authors' Addresses
Naiming Shen
Cisco Systems
560 McCarthy Blvd.
Milpitas, CA 95035
US
Email: naiming@cisco.com
Les Ginsberg
Cisco Systems
821 Alder Drive
Milpitas, CA 95035
US
Email: ginsberg@cisco.com
Sanjay Thyamagundalu
Email: tsanjay@gmail.com
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