Internet DRAFT - draft-cc-ospf-flooding-reduction
draft-cc-ospf-flooding-reduction
Network Working Group H. Chen
Internet-Draft D. Cheng
Intended status: Standards Track Huawei Technologies
Expires: March 24, 2019 M. Toy
Verizon
Y. Yang
IBM
September 20, 2018
LS Flooding Reduction
draft-cc-ospf-flooding-reduction-04
Abstract
This document proposes an approach to flood link states on a topology
that is a subgraph of the complete topology per underline physical
network, so that the amount of flooding traffic in the network is
greatly reduced, and it would reduce convergence time with a more
stable and optimized routing environment. The approach can be
applied to any network topology in a single area.
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].
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 March 24, 2019.
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Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Conventions Used in This Document . . . . . . . . . . . . . . 4
4. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4
5. Flooding Topology . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Construct Flooding Topology . . . . . . . . . . . . . . . 5
5.2. Backup for Flooding Topology Split . . . . . . . . . . . 7
6. Extensions to OSPF . . . . . . . . . . . . . . . . . . . . . 7
6.1. Extensions for Operations . . . . . . . . . . . . . . . . 8
6.2. Extensions for Centralized Mode . . . . . . . . . . . . . 9
6.2.1. Message for Flooding Topology . . . . . . . . . . . . 9
6.2.2. Encodings for Backup Paths . . . . . . . . . . . . . 16
6.2.3. Message for Incremental Changes . . . . . . . . . . . 24
6.2.4. Leaders Selection . . . . . . . . . . . . . . . . . . 25
7. Extensions to IS-IS . . . . . . . . . . . . . . . . . . . . . 27
7.1. Extensions for Operations . . . . . . . . . . . . . . . . 27
7.2. Extensions for Centralized Mode . . . . . . . . . . . . . 27
7.2.1. TLV for Flooding Topology . . . . . . . . . . . . . . 27
7.2.2. Encodings for Backup Paths . . . . . . . . . . . . . 28
7.2.3. TLVs for Incremental Changes . . . . . . . . . . . . 29
7.2.4. Leaders Selection . . . . . . . . . . . . . . . . . . 30
8. Flooding Behavior . . . . . . . . . . . . . . . . . . . . . . 30
8.1. Nodes Perform Flooding Reduction without Failure . . . . 30
8.1.1. Receiving an LS . . . . . . . . . . . . . . . . . . . 30
8.1.2. Originating an LS . . . . . . . . . . . . . . . . . . 31
8.1.3. Establishing Adjacencies . . . . . . . . . . . . . . 31
8.2. An Exception Case . . . . . . . . . . . . . . . . . . . . 32
8.2.1. A Critical Failure . . . . . . . . . . . . . . . . . 32
8.2.2. Multiple Failures . . . . . . . . . . . . . . . . . . 32
9. Security Considerations . . . . . . . . . . . . . . . . . . . 33
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33
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10.1. OSPFv2 . . . . . . . . . . . . . . . . . . . . . . . . . 33
10.2. OSPFv3 . . . . . . . . . . . . . . . . . . . . . . . . . 35
10.3. IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . 36
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 36
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
12.1. Normative References . . . . . . . . . . . . . . . . . . 36
12.2. Informative References . . . . . . . . . . . . . . . . . 37
Appendix A. Algorithms to Build Flooding Topology . . . . . . . 37
A.1. Algorithms to Build Tree without Considering Others . . . 37
A.2. Algorithms to Build Tree Considering Others . . . . . . . 39
A.3. Connecting Leaves . . . . . . . . . . . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42
1. Introduction
For some networks such as dense Data Center (DC) networks, the
existing Link State (LS) flooding mechanism is not efficient and may
have some issues. The extra LS flooding consumes network bandwidth.
Processing the extra LS flooding, including receiving, buffering and
decoding the extra LSs, wastes memory space and processor time. This
may cause scalability issues and affect the network convergence
negatively.
This document proposes an approach to minimize the amount of flooding
traffic in the network. Thus the workload for processing the extra
LS flooding is decreased significantly. This would improve the
scalability, speed up the network convergence, stable and optimize
the routing environment.
This approach is also flexible. It has multiple modes for
computation of flooding topology. Users can select a mode they
prefer, and smoothly switch from one mode to another. The approach
is applicable to any network topology in a single area. It is
backward compatible.
2. Terminology
Flooding Topology:
A sub-graph or sub-network of a given (physical) network topology
that has the same reachability to every node as the given network
topology, through which link states are flooded.
critical link or interface on a flooding topology:
A only link or interface among some nodes on the flooding
topology. When this link or interface goes down, the flooding
topology will be split.
critical node on a flooding topology:
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A only node connecting some nodes on the flooding topology. When
this node goes down, the flooding topology will be split.
backup path:
A path or a sequence of links, when a critical link or node goes
down, providing a connection to connect two parts of a split
flooding topology. When a critical node goes down, the flooding
topology may be split into more than two parts. In this case,
two or more backup paths are needed to connect all the split
parts into one.
Remaining Flooding Topology:
A topology from a flooding topology by removing the failed links
and nodes from the flooding topology.
LSA:
A Link State Advertisement in OSPF.
LSP:
A Link State Protocol Data Unit (PDU) in IS-IS.
LS:
A Link Sate, which is an LSA or LSP.
3. Conventions Used in This Document
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 [RFC2119].
4. Problem Statement
OSPF and IS-IS deploy a so-called reliable flooding mechanism, where
a node must transmit a received or self-originated LS to all its
interfaces (except the interface where an LS is received). While
this mechanism assures each LS being distributed to every node in an
area or domain, the side-effect is that the mechanism often causes
redundant LS, which in turn forces nodes to process identical LS more
than once. This results in the waste of link bandwidth and nodes'
computing resources, and the delay of topology convergence.
This becomes more serious in networks with large number of nodes and
links, and in particular, higher degree of interconnection (e.g.,
meshed topology, spine-leaf topology, etc.). In some environments
such as in data centers, the drawback of the existing flooding
mechanism has already caused operational issues, including repeated
and waves of flooding storms, chock of computing resources, slow
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convergence, oscillating topology changes, instability of routing
environment.
One example is as shown in Figure 1, where Node 1, Node 2 and Node 3
are interconnected in a mesh. When Node 1 receives a new or updated
LS on its interface I11, it by default would forward the LS to its
interface Il2 and I13 towards Node 2 and Node 3, respectively, after
processing. Node 2 and Node 3 upon reception of the LS and after
processing, would potentially flood the same LS over their respective
interface I23 and I32 toward each other, which is obviously not
necessary and at the cost of link bandwidth as well as both nodes'
computing resource.
|
|I11
+--o---+
|Node 1|
+-o--o-+
I12 / \ I13
/ \
I21/ \I31
+----o-+ I32+-o----+
|Node 2|------|Node 3|
+------+I23 +------+
Figure 1
5. Flooding Topology
For a given network topology, a flooding topology is a sub-graph or
sub-network of the given network topology that has the same
reachability to every node as the given network topology. Thus all
the nodes in the given network topology MUST be in the flooding
topology. All the nodes MUST be inter-connected directly or
indirectly. As a result, LS flooding will in most cases occur only
on the flooding topology, that includes all nodes but a subset of
links. Note even though the flooding topology is a sub-graph of the
original topology, any single LS MUST still be disseminated in the
entire network.
5.1. Construct Flooding Topology
Many different flooding topologies can be constructed for a given
network topology. A chain connecting all the nodes in the given
network topology is a flooding topology. A circle connecting all the
nodes is another flooding topology. A tree connecting all the nodes
is a flooding topology. In addition, the tree plus the connections
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between some leaves of the tree and branch nodes of the tree is a
flooding topology.
The following parameters need to be considered for constructing a
flooding topology:
o Number of links: The number of links on the flooding topology is a
key factor for reducing the amount of LS flooding. In general,
the smaller the number of links, the less the amount of LS
flooding.
o Diameter: The shortest distance between the two most distant nodes
on the flooding topology is a key factor for reducing the network
convergence time. The smaller the diameter, the less the
convergence time.
o Redundancy: The redundancy of the flooding topology means a
tolerance to the failures of some links and nodes on the flooding
topology. If the flooding topology is split by some failures, it
is not tolerant to these failures. In general, the larger the
number of links on the flooding topology is, the more tolerant the
flooding topology to failures.
There are many different ways to construct a flooding topology for a
given network topology. A few of them are listed below:
o Central Mode: One node in the network builds a flooding topology
and floods the flooding topology to all the other nodes in the
network (This seems not good. Flooding the flooding topology may
increase the flooding. The amount of traffic for flooding the
flooding topology should be minimized.);
o Distributed Mode: Each node in the network automatically
calculates a flooding topology by using the same algorithm (No
flooding for flooding topology);
o Static Mode: Links on the flooding topology are configured
statically.
Note that the flooding topology constructed by a node is dynamic in
nature, that means when the base topology (the entire topology graph)
changes, the flooding topology (the sub-graph) MUST be re-computed/
re-constructed to ensure that any node that is reachable on the base
topology MUST also be reachable on the flooding topology.
For reference purpose, some algorithms that allow nodes to
automatically compute flooding topology are elaborated in Appendix A.
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However, this document does not attempt to standardize how a flooding
topology is established.
5.2. Backup for Flooding Topology Split
It is hard to construct a flooding topology that reduces the amount
of LS flooding greatly and is tolerant to multiple failures. To get
around this, we can compute and use backup paths for a critical link
and node on the flooding topology. Using backup paths may also speed
up convergence when the link and node fail.
When a critical link on the flooding topology fails, the flooding
topology without the critical link (i.e., the remaining flooding
topology) is split into two parts. A backup path for the critical
link connects the two parts into one. Through the backup path and
the remaining flooding topology, an LS can be flooded to every node
in the network. The combination of the backup path and the flooding
topology is tolerant to the failure of the critical link.
When a critical node on the flooding topology goes down, the flooding
topology without the critical node and the links attached to the node
(i.e., the remaining flooding topology) is split into two or more
parts. One or more backup paths for the critical node connects the
split parts into one. Through the backup paths and the remaining
flooding topology, an LS can be flooded to every live node in the
network. The combination of the backup paths and the flooding
topology is tolerant to the failure of the critical node.
In addition to the backup paths for a critical link and node, backup
paths for every non critical link and node on the flooding topology
can be computed. When the failures of multiple links and nodes on
the flooding topology happen, through the remaining flooding topology
and the backup paths for these links and nodes, an LS can be flooded
to every live node in the network. The combination of the backup
paths and the flooding topology is tolerant to the failures of these
links and nodes. If there are other failures that break the backup
paths, an LS can be flooded to every live node by the traditional
flooding procedure.
In a centralized mode, the leader computes the backup paths and
floods them to all the other nodes. In a distributed mode, every
node computes the backup paths.
6. Extensions to OSPF
The extensions to OSPF comprises two parts: one part is for
operations on flooding reduction, the other is specially for
centralized mode flooding reduction.
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6.1. Extensions for Operations
A new TLV is defined in OSPF RI LSA [RFC7770]. It contains
instructions about flooding reduction, which is called Flooding
Reduction Instruction TLV or Instruction TLV for short. This TLV is
originated from only one node at any time.
The format of a Flooding Reduction Instruction TLV is as follows.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INST-TLV-Type (TBD1) | TLV-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OP | MOD | Algorithm | Reserved (MUST be zero) | NL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ sub TLVs (optional) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flooding Reduction Instruction TLV
A OP field of three bits is defined in the TLV. It may have a value
of the followings.
o 0x001 (R): Perform flooding Reduction, which instructs the nodes
in a network to perform flooding reduction.
o 0x010 (N): Roll back to Normal flooding, which instructs the nodes
in a network to roll back to perform normal flooding.
When any of the other values is received, it is ignored.
A MOD field of three bits is defined in the TLV and may have a value
of the followings.
o 0x001 (C): Central Mode, which instructs 1) the nodes in a network
to select leaders (primary/designated leader, secondary/backup
leader, and so on); 2) the leaders in a network to compute a
flooding topology and the primary leader to flood the flooding
topology to all the other nodes in the network; 3) every node in
the network to receive and use the flooding topology originated by
the primary leader.
o 0x010 (D): Distributed Mode, which instructs every node in a
network to compute and use its own flooding topology.
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o 0x011 (S): Static Mode, which instructs every node in a network to
use the flooding topology statically configured on the node.
When any of the other values is received, it is ignored.
An Algorithm field of eight bits is defined in the TLV to instruct
the leader node in central mode or every node in distributed mode to
use the algorithm indicated in this field for computing a flooding
topology.
A NL field of three bits is defined in the TLV, which indicates the
number of leaders to be selected when Central Mode is used. NL set
to 2 means two leaders (a designated/primary leader and a backup/
secondary leader) to be selected for an area, and NL set to 3 means
three leaders to be selected. When Central Mode is not used, The NL
field is not valid.
Some optional sub TLVs may be defined in the future, but none is
defined now.
6.2. Extensions for Centralized Mode
6.2.1. Message for Flooding Topology
A flooding topology can be represented by the links in the flooding
topology. For the links between a local node and a number of its
adjacent (or remote) nodes, we can encode the local node in a way,
and encode its adjacent nodes in the same way or another way. After
all the links in the flooding topology are encoded, the encoded links
can be flooded to every node in the network. After receiving the
encoded links, every node decodes the links and creates and/or
updates the flooding topology.
For every node in an area, we may use an index to represent it.
Every node in an area may order the nodes in a rule, which generates
the same sequence of the nodes on every node in the area. The
sequence of nodes have the index 0, 1, 2, and so on respectively.
For example, every node orders the nodes by their router IDs in
ascending order.
6.2.1.1. Links Encoding
A local node can be encoded in two parts: encoded node index size
indication (ENSI) and compact node index (CNI). ENSI value plus a
number (e.g., 9) gives the size of compact node index. For example,
ENSI = 0 indicates that the size of CNIs is 9 bits. In the figure
below, Local node LN1 is encoded as ENSI=0 using 3 bits and CNI=LN1's
Index using 9 bits. LN1 is encoded in 12 bits in total.
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0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+-+
|0 0 0| ENSI (3 bits) [9 bits CNI]
+-+-+-+-+-+-+-+-+-+
| LN1 Index Value | CNI (9 bits)
+-+-+-+-+-+-+-+-+-+
An Example of Local Node Encoding
The adjacent nodes can be encoded in two parts: Number of Nodes (NN)
and compact node indexes (CNIs). The size of CNIs is the same as the
local node. For example, three adjacent nodes RN1, RN2 and RN3 are
encoded below in 30 bits (i.e., 3.75 bytes).
0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+-+
|0 1 1| NN (3 bits) [3 adjacent nodes]
+-+-+-+-+-+-+-+-+-+
| RN1's Index | CNI (9 bits) for RN1
+-+-+-+-+-+-+-+-+-+
| RN2's Index | CNI (9 bits) for RN2
+-+-+-+-+-+-+-+-+-+
| RN3's Index | CNI (9 bits) for RN3
+-+-+-+-+-+-+-+-+-+
An Example of Adjacent Nodes Encoding
The links between a local node and a number of its adjacent (or
remote) nodes can be encoded as the local node followed by the
adjacent nodes. For example, three links between local node LN1 and
its three adjacent nodes RN1, RN2 and RN3 are encoded below in 42
bits (i.e., 5.25 bytes).
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0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+-+ _
|0 0 0| ENSI (3 bits) [9 bits CNI] |
+-+-+-+-+-+-+-+-+-+ } Encoding for
| LN1 Index Value | CNI (9 bits) for LN1 _| Local Node LN1
+-+-+-+-+-+-+-+-+-+ _
|0 1 1| NN (3 bits) [3 nodes] |
+-+-+-+-+-+-+-+-+-+ | Encoding for
| RN1's Index | CNI (9 bits) for RN1 | 3 adjacent nodes
+-+-+-+-+-+-+-+-+-+ } RN1, RN2, RN3
| RN2's Index | CNI (9 bits) for RN2 | of LN1
+-+-+-+-+-+-+-+-+-+ |
| RN3's Index | CNI (9 bits) for RN3 _|
+-+-+-+-+-+-+-+-+-+
An Example of Links Encoding
For a flooding topology computed by a leader of an area, it may be
represented by all the links on the flooding topology. A Type-
Length-Value (TLV) of the following format for the links encodings
can be included in an LSA to represent the flooding topology (FT) and
flood the FT to every node in the area.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FTLK-TLV-Type (TBD2) | TLV-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Links Encoding (Node 1 to its adjacent Nodes) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Links Encoding (Node 2 to its adjacent Nodes) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: :
Flooding Topology Links TLV
Note that a link between a local node LN and its adjacent node RN can
be encoded once and as a bi-directional link. That is that if it is
encoded in a Links Encoding from LN to RN, then the link from RN to
LN is implied or assumed.
For OSPFv2, an Opaque LSA of a new opaque type (TBD3) containing a
Flooding Topology Links TLV is used to flood the flooding topology
from the leader of an area to all the other nodes in the area.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | LS Type = 10 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FT-Type(TBD3) | Instance ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Flooding Topology Links TLV ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OSPFv2: Flooding Topology Opaque LSA
For OSPFv3, an area scope LSA of a new LSA function code (TBD4)
containing a Flooding Topology Links TLV is used to flood the
flooding topology from the leader of an area to all the other nodes
in the area.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age |1|0|1| FT-LSA (TBD4) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Flooding Topology Links TLV ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OSPFv3: Flooding Topology LSA
The U-bit is set to 1, and the scope is set to 01 for area-scoping.
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6.2.1.2. Block Encoding
Block encoding uses a single structure to encode a block (or part) of
topology, which can be a block of links in a flooding topology. It
can also be all the links in the flooding topology. It starts with a
local node LN and its adjacent (or remote) nodes RNi (i = 1, 2, ...,
n), and can be considered as an extension to the links encoding.
The encoding of links between a local node and its adjacent nodes
described in Section 6.2.1.1 is extended to include the links
attached to the adjacent nodes.
The encoding for the adjacent nodes is extended to include Extending
Flags (E Flags for short) between the NN (Number of Nodes) field and
the CNIs (Compact Node Indexes) for the adjacent nodes. The length
of the E Flags field is NN bits. The following is an example
encoding of the adjacent nodes with E Flags of 3 bits, which is the
value of the NN (the number of adjacent nodes).
0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+-+
|0 1 1| NN (3 bits) [3 adjacent nodes]
+-+-+-+
|1 0 1| E Flags [NN=3 bits]
+-+-+-+-+-+-+-+-+-+
| RN1's Index | CNI (9 bits) for RN1
+-+-+-+-+-+-+-+-+-+
| RN2's Index | CNI (9 bits) for RN2
+-+-+-+-+-+-+-+-+-+
| RN3's Index | CNI (9 bits) for RN3
+-+-+-+-+-+-+-+-+-+
An Example of Adjacent Nodes with E Flags Encoding
There is a bit flag (called E flag) in the E Flags field for each
adjacent node. The first bit (i.e., the most significant bit) in the
E Flags field is for the first adjacent node (e.g., RN1), the second
bit is for the second adjacent node (e.g., RN2), and so on. The E
flag for an adjacent node RNi set to one indicates that the links
attached to the adjacent node RNi are included below. The E flag for
an adjacent node RNi set to zero means that no links attached to the
adjacent node RNi are included below.
The links attached to the adjacent node RNi are represented by the
RNi as a local node and the adjacent nodes of RNi. The encoding for
the adjacent nodes of RNi is the same as that for the adjacent nodes
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of a local node. It consists of an NN field of 3 bits, E Flags field
of NN bits, and CNIs for the adjacent nodes of RNi.
The following is an example of a block encoding for a block (or part)
of flooding topology below.
o LN1
/ | \
/ \
/ | \
o RN1 o RN2 o RN3
/ / \
/ / \
/ / \
o RN11 o RN31 o RN32
An Example Block of Flooding Topology
It represents 6 links: 3 links between local node LN1 and its 3
adjacent nodes RN1, RN2 and RN3; 1 link between RN1 as a local node
and its 1 adjacent node RN11; and 2 links between RN3 as a local node
and its 2 adjacent nodes RN31 and RN32.
It starts with the encoding of the links between local node LN1 and 3
adjacent nodes RN1, RN2 and RN3 of the local node LN1. The encoding
for the local node LN1 is the same as that for a local node described
in Section 6.2.1.1. The encoding for 3 adjacent nodes RN1, RN2 and
RN3 of local node LN1 comprises an NN field of 3 bits with value of
3, E Flags field of NN = 3 bits, and the indexes of adjacent nodes
RN1, RN2 and RN3.
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0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+-+ _
|0 0 0| ENSI (3 bits) [9 bits CNI] |
+-+-+-+-+-+-+-+-+-+ } Encoding for
| LN1 Index Value | CNI (9 bits) _| Local Node LN1
+-+-+-+-+-+-+-+-+-+ _
|0 1 1| NN(3 bits)[3 adjacent nodes]|
+-+-+-+ |
|1 0 1| E Flags [NN=3 bits] | Encoding for
+-+-+-+-+-+-+-+-+-+ | 3 adjacent nodes
| RN1's Index | CNI (9 bits) for RN1 } (RN1, RN2, RN3)
+-+-+-+-+-+-+-+-+-+ | of LN1
| RN2's Index | CNI (9 bits) for RN2 |
+-+-+-+-+-+-+-+-+-+ |
| RN3's Index | CNI (9 bits) for RN3 _|
+-+-+-+-+-+-+-+-+-+ _
|0 0 1| NN (3 bits)[1 adjacent node]|
+-+-+-+ | Encoding for
|0| E Flags [NN=1 bit] } 1 adjacent node
+-+-+-+-+-+-+-+-+-+ | (RN11)
| RN11's Index | CNI (9 bits) for RN11 _| of RN1
+-+-+-+-+-+-+-+-+-+ _
|0 1 0| NN(3 bits)[2 adjacent nodes]|
+-+-+-+ |
|0 0| E Flags [NN=2 bits] | Encoding for
+-+-+-+-+-+-+-+-+-+ } 2 adjacent nodes
| RN31's Index | CNI (9 bits) for RN31 | (RN31, RN32)
+-+-+-+-+-+-+-+-+-+ | of RN3 as a
| RN32's Index | CNI (9 bits) for RN32 | local node
+-+-+-+-+-+-+-+-+-+ _|
An Example of Block Encoding
The first E flag in the encoding for adjacent nodes RN1, RN2 and RN3
is set to one, which indicates that the links between the first
adjacent node RN1 as a local node and its adjacent nodes are included
below. In this example, 1 link between RN1 and its adjacent node
RN11 is represented by the encoding for the adjacent node RN11 of RN1
as a local node. The encoding for 1 adjacent node RN11 consists of
an NN field of 3 bits with value of 1, E Flags field of NN = 1 bits,
and the index of adjacent node RN11. The size of the index of RN11
is the same as that of local node LN1 indicated by the ENSI in the
encoding for local node LN1.
The second E flag in the encoding for adjacent nodes RN1, RN2 and RN3
is set to zero, which indicates that no links between the second
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adjacent node RN2 as a local node and its adjacent nodes are included
below.
The third E flag in the encoding for adjacent nodes RN1, RN2 and RN3
is set to one, which indicates that the links between the third
adjacent node RN3 as a local node and its adjacent nodes are included
below. In this example, 2 links between RN3 and its 2 adjacent nodes
RN31 and RN32 are represented by the encoding for the adjacent nodes
RN31 and RN32 of RN3 as a local node. The encoding for 2 adjacent
nodes RN31 and RN32 consists of an NN field of 3 bits with value of
2, E Flags field of NN = 2 bits, and the indexes of adjacent nodes
RN31 and RN32. The size of the index of RN31 and RN32 is the same as
that of local node LN1 indicated by the ENSI in the encoding for
local node LN1.
The block encoding may be used in the place of the links encoding in
Section 6.2.1.1 for more efficiency. That is that it may be used in
a Flooding Topology Links TLV. Alternatively, a new TLV, which is
similar to the Flooding Topology Links TLV, may be defined to contain
a number of block encodings.
6.2.2. Encodings for Backup Paths
When the leader of an area computes a flooding topology, it may
compute a backup path or multiple backup paths for a critical link on
the flooding topology. When the critical link fails, a link state
can be distributed to every node in the area through one backup path
and other links on the flooding topology. In addition, it may
compute a backup path or multiple backup paths for a node. When the
node fails, a link state can be distributed to the other nodes in the
area through the backup paths and the links on the flooding topology.
This section describes two encodings for backup paths: separated
encoding and integrated one. In the former, backup paths are encoded
in a new message, where the message for the flooding topology
described in the previous section is required; In the latter, backup
paths are integrated into the flooding topology links encoding, where
one message contains the flooding topology and the backup paths.
6.2.2.1. Message for Backup Paths
Backup paths for a node (such as Node1) may be represented by the
node index encoding and node backup paths encoding. The former is
similar to local node index encoding. The latter has the following
format. It comprises a K flag (Key/Critical node flag) of 1 bit, a 3
bits NNBP field (number of node backup paths), and each of the backup
paths encoding, which consists of the path length PLEN of 4 bits
indicating the length of the path (i.e., the number of nodes), and
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the encoding of the sequence of nodes along the path such as
encodings for nodes PN1, ..., PNn. The encoding of every node may
use the encoding of a local node, which comprises encoded node index
size indication (ENSI) and compact node index (CNI).
0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+
|K| 1 bit (K=1: Key/Critical Node, K=0: Normal Node)
+-+-+-+ _
|NNBP | 3 bits (number of node backup paths) |
+-+-+-+-+ _ |
|PLEN | 4 bits (backup path len) | |
+-+-+-+-+-+-+-+-+ | | Backup
| PN1 Encoding | Variable bits | One } paths
+-+-+-+-+-+-+-+-+ } backup path | for Node
~ ~ | for Node |
+-+-+-+-+-+-+-+-+ | |
| PNn Encoding | Variable bits _| |
+-+-+-+-+-+-+-+-+ |
// // _|
An Example of Node Backup Paths Encoding
Another encoding of the sequence of nodes along the path uses one
encoded node index size indication (ENSI) for all the nodes in the
path. Thus we have the following Node Backup Paths Encoding.
0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+
|K| 1 bit (K=1: Key/Critical Node, K=0: Normal Node)
+-+-+-+ _
|NNBP | 3 bits (number of node backup paths) |
+-+-+-+-+ _ |
|PLEN | 4 bits (backup path len) | |
+-+-+-+-+ | |
|ENSI | 3 bits(Ix Bits Indication)| | Backup
+-+-+-+-+-+-+-+-+ | One } paths
| PN1 Index | #Bits indicated by ENSI } backup path | for Node
+-+-+-+-+-+-+-+-+ | for Node |
~ ~ | |
+-+-+-+-+-+-+-+-+ | |
| PNn Index | #Bits indicated by ENSI _| |
+-+-+-+-+-+-+-+-+ |
// // _|
Another Example of Node Backup Paths Encoding
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A new TLV called Node Backup Paths TLV is defined below. It may
include multiple nodes and their backup paths. Each node is
represented by its index encoding, which is followed by its node
backup paths encoding.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NBP-TLV-Type (TBD5) | TLV-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Node1 Index Enc| Variable bits
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Node1 backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Node2 Index Enc| Variable bits
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Node2 backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
Node Backup Paths TLV
The encoding for backup paths for a link (such as Link1) on the
flooding topology consists of the link encoding such as Link1 Index
Encoding and the link backup paths encoding. The former is similar
to local node encoding. It contains encoded link index size
indication (ELSI) and compact link index (CLI). The latter has the
following format. It comprises a C flag (Critical link flag) of 1
bit, a 2 bits NLB field (number of link backup paths), and each of
the backup paths encoding, which consists of the path length PLEN of
3 bits indicating the length of the path (i.e., the number of nodes),
and the encoding of the sequence of nodes along the path such as
encodings for nodes PN1, ..., PNm. Note that two ends of a link
(i.e., the local node and the adjacent/remote node of the link) are
not needed in the path. The encoding of every node may use the
encoding of a local node, which comprises encoded node index size
indication (ENSI) and compact node index (CNI).
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0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+
|C| 1 bit (C=1: Critical Link, C=0: Normal Link)
+-+-+ _
|NLB| 2 bits (number of link backup paths) |
+-+-+-+ _ |
|PLEN | 3 bits (backup path len) | |
+-+-+-+-+-+-+-+-+ | | Backup
| PN1 Encoding | Variable bits | One } paths
+-+-+-+-+-+-+-+-+ } backup path | for Link
~ ~ | for Link |
+-+-+-+-+-+-+-+-+ | |
| PNm Encoding | Variable bits _| |
+-+-+-+-+-+-+-+-+ |
// // _|
An Example of Link Backup Paths Encoding
Another encoding of the sequence of nodes along the path uses one
encoded node index size indication (ENSI) for all the nodes in the
path. Thus we have the following Link Backup Paths Encoding.
0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+
|C| 1 bit (C=1: Critical Link, C=0: Normal Link)
+-+-+ _
|NLB| 2 bits (number of link backup paths) |
+-+-+-+ _ |
|PLEN | 3 bits (backup path len) | |
+-+-+-+ | |
|ENSI | 3 bits(Ix Bits Indication)| | Backup
+-+-+-+-+-+-+-+-+ | One } paths
| PN1 Index | #Bits indicated by ENSI } backup path | for Link
+-+-+-+-+-+-+-+-+ | for Link |
~ ~ | |
+-+-+-+-+-+-+-+-+ | |
| PNm Index | #Bits indicated by ENSI _| |
+-+-+-+-+-+-+-+-+ |
// // _|
Another Example of Link Backup Paths Encoding
A new TLV called Link Backup Paths TLV is defined below. It may
include multiple links and their backup paths. Each link is
represented by its index encoding, which is followed by its link
backup paths encoding.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LBP-TLV-Type (TBD6) | TLV-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Link1 Index Enc| Variable bits
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Link1 backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Link2 Index Enc| Variable bits
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Link2 backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
Link Backup Paths TLV
For OSPFv2, an Opaque LSA of a new opaque type (TBD7), containing
node backup paths TLVs and link backup paths TLVs, is used to flood
the backup paths from the leader of an area to all the other nodes in
the area.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | LS Type = 10 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BP-Type(TBD7) | Instance ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Link Backup Paths TLVs ~
~ Node Backup Paths TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OSPFv2: Backup Paths Opaque LSA
For OSPFv3, an area scope LSA of a new LSA function code (TBD8),
containing node backup paths TLVs and link backup paths TLVs, is used
to flood the backup paths from the leader of an area to all the other
nodes in the area.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age |1|0|1| BP-LSA (TBD8) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Link Backup Paths TLVs ~
~ Node Backup Paths TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OSPFv3: Backup Paths LSA
The U-bit is set to 1, and the scope is set to 01 for area-scoping.
6.2.2.2. Backup Paths in Links TLV
A local node and its backup paths can be encoded in the following
format. It is the local node (such as local node LN1) encoding
followed by the local node backup paths encoding, which is the same
as the node backup paths encoding described in Section 6.2.2.1.
0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+-+ _
|ENSI | 3 bits(#bits indication) |
+-+-+-+-+-+-+-+-+-+ } Local Node LN1
| LN1 Index Value | #bits indicated by ENSI _| Encoding
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Local node LN1 backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Local Node with Backup Paths Encoding
A adjacent node and its backup paths can be encoded in the following
format. It is the adjacent node (such as adjacent node RN10) index
value followed by the adjacent node backup paths encoding, which is
the same as the node backup paths encoding described in
Section 6.2.2.1.
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+-+-+-+-+-+-+-+-+-+
|RN10 Index Value | (#bits indicated by ENSI)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: adjacent node RN10 backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Adjacent Node with Backup Paths Encoding
The links between a local node and a number of its adjacent nodes,
the backup paths for each of the nodes, and the backup paths for each
of the links can be encoded in the following format. It is called
Links from Node with Backup Paths Encoding.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Local Node with backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NN | Number of adjacent Nodes (i.e., Number of links)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Adjacent Node 1 with backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Link1 backup paths Encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Adjacent Node 2 with backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Link2 backup paths Encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
Links from Node with Backup Paths Encoding
A new TLV called Links with Backup Paths TLV is defined below. It
includes a number of Links from Node with Backup Paths Encodings
described above. This TLV contains both the flooding topology and
the backup paths for the links and nodes on the flooding topology.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LNSBP-TLV-Type (TBD9) | TLV-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Links from Node 1 with backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Links from Node 2 with backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: :
Links with Backup Paths TLV
For OSPFv2, an Opaque LSA of a new opaque type (TBDa), called
Flooding Topology with Backup Paths (FTBP) Opaque LSA, containing a
Links with Backup Paths TLV, is used to flood the flooding topology
with backup paths from the leader of an area to all the other nodes
in the area.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | LS Type = 10 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|FTBP-Type(TBDa)| Instance ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Links with Backup Paths TLV ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OSPFv2: Flooding Topology with Backup Paths (FTBP) Opaque LSA
For OSPFv3, an area scope LSA of a new LSA function code (TBDb),
containing a Links with Backup Paths TLV, is used to flood the
flooding topology with backup paths from the leader of an area to all
the other nodes in the area.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age |1|0|1| FTBP-LSA (TBDb) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Links with Backup Paths TLV ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OSPFv3: Flooding Topology with Backup Paths (FTBP) LSA
6.2.3. Message for Incremental Changes
For adding some links to the flooding topology, we define a new TLV
called Add Links TLVs of the following format. When some new links
are added to the flooding topology, the leader may not flood the
whole flooding topology with the new links to all the other nodes.
It may just flood these new links. After receiving these new links,
each of the other nodes adds these new links into the existing
flooding topology. When the leader floods the whole flooding
topology with the new links to all the other nodes, it removes the
LSA for the new links. When removing the LSA for these new links,
each of the other nodes does not update the flooding topology (i.e.,
does not remove these links from the flooding topology).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ADDLK-TLV-Type (TBDc) | TLV-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Links Encoding (Node 1 to its adjacent Nodes) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Links Encoding (Node 2 to its adjacent Nodes) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: :
Add Links TLV
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For deleting some links from the flooding topology, we define a new
TLV called Delete Links TLVs of the following format. When some old
links are removed from the flooding topology, the leader may not
flood the whole flooding topology without the old links to all the
other nodes. It may just flood these old links. After receiving
these old links, each of the other nodes deletes these old links from
the existing flooding topology. When the leader floods the whole
flooding topology without the old links to all the other nodes, it
removes the LSA for the old links. When removing the LSA for these
old links, each of the other nodes does not update the flooding
topology (i.e., does not add these links into the flooding topology).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DELLK-TLV-Type (TBDd) | TLV-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Links Encoding (Node 1 to its adjacent Nodes) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Links Encoding (Node 2 to its adjacent Nodes) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: :
Delete Links TLV
The Add Links TLVs and Delete Links TLVs should be in a separate LSA
instance. The LSA can be a Flooding Topology LSA defined above.
Alternatively, we may define a new LSA for these TLVs.
6.2.4. Leaders Selection
The leader or Designated Router (DR) selection for a broadcast link
is about selecting two leaders: a DR and Backup DR. This is
generalized to select two or more leaders for an area: the primary/
first leader (or leader for short), the secondary leader, the third
leader and so on.
A new TLV is defined to include the information on flooding reduction
of a node, which is called Flooding Reduction Information TLV or
Information TLV for short. This TLV is generated by every node that
supports flooding reduction in general. Every node originates a RI
LSA with a Flooding Reduction Information TLV containing its priority
to become a leader. The format of the TLV is as follows.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INFO-TLV-Type (TBDe) | TLV-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | Reserved (MUST be zero) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ sub TLVs (optional) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flooding Reduction Information TLV
A Priority field of eight bits is defined in the TLV to indicate the
priority of the node originating the TLV to become the leader node in
central mode.
A sub-TLV called leaders sub-TLV is defined. It has the following
format.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LEADS-TLV-Type (TBDf) | TLV-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1st Leader Node/Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2nd Leader Node/Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| nth Leader Node/Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Leaders sub-TLV
When a node selects itself as a leader, it originates a RI LSA
containing the leader in a leaders sub-TLV.
After the first leader node is down, the other leaders will be
promoted. The secondary leader becomes the first leader, the third
leader becomes the secondary leader, and so on. When a node selects
itself as the n-th leader, it originates a RI LSA with a Leaders sub-
TLV containing n leaders.
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7. Extensions to IS-IS
The extensions to IS-IS is similar to OSPF.
7.1. Extensions for Operations
A new TLV for operations is defined in IS-IS LSP. It has the
following format and contains the same contents as the Flooding
Reduction Instruction TLV defined in OSPF RI LSA.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|INST-Type(TBDi1| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OP | MOD | Algorithm | Reserved (MUST be zero) | NL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ sub TLVs (optional) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IS-IS Flooding Reduction Instruction TLV
7.2. Extensions for Centralized Mode
7.2.1. TLV for Flooding Topology
A new TLV for the encodings of the links in the flooding topology is
defined. It has the following format and contains the same contents
as the Flooding Topology Links TLV defined in OSPF Flooding Topology
Opaque LSA.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|FTL-Type(TBDi2)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Links Encoding (Node 1 to its adjacent Nodes) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Links Encoding (Node 2 to its adjacent Nodes) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: :
IS-IS Flooding Topology Links TLV
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7.2.2. Encodings for Backup Paths
7.2.2.1. TLVs for Backup Paths
For flooding backup paths separately, we define two TLVs: IS-IS Node
Backup Paths TLV and IS-IS Link Backup Path TLV. The former has the
following format and contains the same contents as Node Backup Paths
TLV in OSPF.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|NBP-Type(TBDi3)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Node1 Index Enc| Variable bits
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Node1 backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Node2 Index Enc| Variable bits
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Node2 backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
IS-IS Node Backup Paths TLV
The latter has the following format and contains the same contents as
Link Backup Paths TLV in OSPF.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|LBP-Type(TBDi4)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Link1 Index Enc| Variable bits
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Link1 backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Link2 Index Enc| Variable bits
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Link2 backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// //
IS-IS Link Backup Paths TLV
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7.2.2.2. Backup Paths in Links TLV
A new TLV is defined to integrate the backup paths with the links on
the flooding topology. It has the following format and contains the
same contents as the Links with Backup Paths TLV in OSPF.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|LSB-Type(TBDi5)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Links from Node 1 with backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Links from Node 2 with backup paths encoding :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: :
IS-IS Links with Backup Paths TLV
7.2.3. TLVs for Incremental Changes
Similar to Add Links TLV in OSPF, a new TLV called IS-IS Add Links
TLV is defined. It has the following format and contains the same
contents as Add Links TLV in OSPF.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|ADDL-Type(TBDi6| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Links Encoding (Node 1 to its adjacent Nodes) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Links Encoding (Node 2 to its adjacent Nodes) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: :
IS-IS Add Links TLV
Similar to Delete Links TLV in OSPF, a new TLV called IS-IS Delete
Links TLV is defined. It has the following format and contains the
same contents as Delete Links TLV in OSPF.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|DELL-Type(TBDi7| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Links Encoding (Node 1 to its adjacent Nodes) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Links Encoding (Node 2 to its adjacent Nodes) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: :
: :
IS-IS Delete Links TLV
7.2.4. Leaders Selection
Similar to Flooding Reduction Information TLV in OSPF, a new TLV
called IS-IS Flooding Reduction Information TLV is defined. It has
the following format and contains the same contents as Flooding
Reduction Information TLV in OSPF.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|INF-Type(TBDi8)| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | Reserved (MUST be zero) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ sub TLVs (optional) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IS-IS Flooding Reduction Information TLV
8. Flooding Behavior
This section describes the revised flooding behavior for a node
having at least one link on the flooding topology. The revised
flooding procedure MUST flood an LS to every node in the network in
any case, as the standard flooding procedure does.
8.1. Nodes Perform Flooding Reduction without Failure
8.1.1. Receiving an LS
When a node receives a newer LS that is not originated by itself from
one of its interfaces, it floods the LS only to all the other
interfaces that are on the flooding topology.
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When the LS is received from an interface on the flooding topology,
it is flooded only to all the other interfaces that are on the
flooding topology. When the LS is received on an interface that is
not on the flooding topology, it is also flooded only to all the
other interfaces that are on the flooding topology.
In any case, the LS must not be transmitted back to the receiving
interface.
Note before forwarding a received LS, the node would do the normal
processing as usual.
8.1.2. Originating an LS
When a node originates an LS, it floods the LS to its interfaces on
the flooding topology if the LS is a refresh LS (i.e., there is no
significant change in the LS comparing to the previous LS); otherwise
(i.e., there are significant changes in the LS), it floods the LS to
all its interfaces. Choosing flooding the LS with significant
changes to all the interfaces instead of limiting to the interfaces
on the flooding topology would speed up the distribution of the
significant link state changes.
8.1.3. Establishing Adjacencies
Adjacencies being established can be classified into two categories:
adjacencies to new nodes and adjacencies to existing nodes.
8.1.3.1. Adjacency to New Node
An adjacency to a new node is an adjacency between a node (say node
A) on the flooding topology and the new node (say node Y) which is
not on the flooding topology. There is not any adjacency between
node Y and a node in the network area.
When new node Y is up and connected to node A, node A assumes that
node Y and the link between node Y and node A are on the flooding
topology until a new flooding topology is computed and built. Node A
may determine whether node Y is a new node through checking if node Y
is reachable or on the flooding topology.
The procedure for establishing the adjacency between node A and node
Y is the existing normal procedure unchanged. After the status of
the adjacency reaches to Exchange or Full, node A sends node Y every
new or updated LS that node A receives or originates.
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8.1.3.2. Adjacency to Existing Node
An adjacency to an existing node is an adjacency between a node (say
node A) on the flooding topology and the existing node (say node X)
which exists on the flooding topology. There are some adjacencies
between node X and some nodes in the network area.
When existing node X is connected to node A after a link between node
X and node A is up, node A assumes that the link connecting node A
and node X is not on the flooding topology until a new flooding
topology is computed and built. Node A may determine whether node X
is an existing node through checking if node X is reachable or on the
flooding topology.
The procedure for establishing the adjacency between node A and node
X is the existing normal procedure unchanged. Node A does not send
node X any new or updated LS that node A receives or originates even
after the status of the adjacency reaches to Exchange or Full.
8.2. An Exception Case
During an LS flooding, one or multiple link and node failures may
happen. Some failures do not split the flooding topology, thus do
not affect the flooding behavior. For example, multiple failures of
the links not on the flooding topology do not split the flooding
topology and do not affect the flooding behavior. The sections below
focus on the failures that may split the flooding topology.
8.2.1. A Critical Failure
For a link failure, if the link is a critical link on the flooding
topology, then the LS is flooded through a backup path for the link
and the remaining flooding topology until a new flooding topology is
computed and built; otherwise, the flooding behavior in Section 8.1
follows.
Similarly, for a node failure, if the node is a critical node on the
flooding topology, then the LS is flooded through backup paths for
the node and the remaining flooding topology until a new flooding
topology is computed and built; otherwise, the flooding behavior in
Section 8.1 follows.
8.2.2. Multiple Failures
For multiple link failures, if the number of the failed links on the
flooding topology is greater than or equal to two, then the LS is
flooded through a backup path for each of the failed links on the
flooding topology and the remaining flooding topology until a new
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flooding topology is computed and built; otherwise, the flooding
behavior in Section 8.1 follows.
If all the backup paths for some of the failed links are broken by
some failures, the LS is flooded to all interfaces (except where it
is received from) until a new flooding topology is computed and
built.
For multiple node failures, the LS is flooded through the backup
paths for each of the failed nodes and the remaining flooding
topology until a new flooding topology is computed and built;
otherwise, the flooding behavior in Section 8.1 follows.
If the backup paths for some of the failed nodes are broken by some
failures, the LS is flooded to all interfaces (except where it is
received from) until a new flooding topology is computed and built.
Note that if it can be quickly determined that the flooding topology
is not split by the failures, the flooding behavior in Section 8.1
may follow.
9. Security Considerations
This document does not introduce any security issue.
10. IANA Considerations
10.1. OSPFv2
Under Registry Name: OSPF Router Information (RI) TLVs [RFC7770],
IANA is requested to assign two new TLV values for OSPF flooding
reduction as follows:
+===============+==================+=====================+
| TLV Value | TLV Name | reference |
+===============+==================+=====================+
| 11 | Instruction TLV | This document |
+---------------+------------------+---------------------+
| 12 | Information TLV | This document |
+---------------+------------------+---------------------+
Under the registry name "Opaque Link-State Advertisements (LSA)
Option Types" [RFC5250], IANA is requested to assign new Opaque Type
registry values for FT LSA, BP LSA, FTBP LSA as follows:
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+====================+===============+=======================+
| Registry Value | Opaque Type | reference |
+====================+===============+=======================+
| 10 | FT LSA | This document |
+--------------------+---------------+-----------------------+
| 11 | BP LSA | This document |
+--------------------+---------------+-----------------------+
| 12 | FTBP LSA | This document |
+--------------------+---------------+-----------------------+
IANA is requested to create and maintain new registries:
o OSPFv2 FT LSA TLVs
Initial values for the registry are given below. The future
assignments are to be made through IETF Review [RFC5226].
Value OSPFv2 FT LSA TLV Name Definition
----- ----------------------- ----------
0 Reserved
1 FT Links TLV see Section 6.2.1
2-32767 Unassigned
32768-65535 Reserved
o OSPFv2 BP LSA TLVs
Initial values for the registry are given below. The future
assignments are to be made through IETF Review [RFC5226].
Value OSPFv2 TBPLSA TLV Name Definition
----- ----------------------- ----------
0 Reserved
1 Node Backup Paths TLV see Section 6.2.2
2 Link Backup Paths TLV see Section 6.2.2
3-32767 Unassigned
32768-65535 Reserved
o OSPFv2 FTBP LSA TLVs
Initial values for the registry are given below. The future
assignments are to be made through IETF Review [RFC5226].
Value OSPFv2 FTBP LSA TLV Name Definition
----- ------------------------ ----------
0 Reserved
1 Links with Backup Paths TLV see Section 6.2.2
2-32767 Unassigned
32768-65535 Reserved
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10.2. OSPFv3
Under the registry name "OSPFv3 LSA Function Codes", IANA is
requested to assign new registry values for FT LSA, BP LSA, FTBP LSA
as follows:
+===========+==========================+=======================+
| Value | LSA Function Code Name | reference |
+======================================+=======================+
| 16 | FT LSA | This document |
+-----------+--------------------------+-----------------------+
| 17 | BP LSA | This document |
+-----------+--------------------------+-----------------------+
| 18 | FTBP LSA | This document |
+-----------+--------------------------+-----------------------+
IANA is requested to create and maintain new registries:
o OSPFv3 FT LSA TLVs
Initial values for the registry are given below. The future
assignments are to be made through IETF Review [RFC5226].
Value OSPFv3 FT LSA TLV Name Definition
----- ----------------------- ----------
0 Reserved
1 FT Links TLV see Section 6.2.1
2-32767 Unassigned
32768-65535 Reserved
o OSPFv3 BP LSA TLVs
Initial values for the registry are given below. The future
assignments are to be made through IETF Review [RFC5226].
Value OSPFv3 TBPLSA TLV Name Definition
----- ----------------------- ----------
0 Reserved
1 Node Backup Paths TLV see Section 6.2.2
2 Link Backup Paths TLV see Section 6.2.2
3-32767 Unassigned
32768-65535 Reserved
o OSPFv3 FTBP LSA TLVs
Initial values for the registry are given below. The future
assignments are to be made through IETF Review [RFC5226].
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Value OSPFv3 FTBP LSA TLV Name Definition
----- ------------------------ ----------
0 Reserved
1 Links with Backup Paths TLV see Section 6.2.2
2-32767 Unassigned
32768-65535 Reserved
10.3. IS-IS
Under Registry Name: IS-IS TLV Codepoints, IANA is requested to
assign new TLV values for IS-IS flooding reduction as follows:
Value TLV Name Definition
----- ------------------------ ----------
151 FT Links TLV see Section 7.2.1
152 Node Backup Paths TLV see Section 7.2.2
153 Link Backup Paths TLV see Section 7.2.2
154 Links with Backup Paths TLV see Section 7.2.2
155 Add Links TLV see Section 7.2.3
156 Delete Links TLV see Section 7.2.3
157 Instruction TLV see Section 7.1
158 Information TLV see Section 7.2.4
11. Acknowledgements
The authors would like to thank Acee Lindem, Zhibo Hu, Robin Li,
Stephane Litkowski and Alvaro Retana for their valuable suggestions
and comments on this draft.
12. References
12.1. Normative References
[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>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250,
July 2008, <https://www.rfc-editor.org/info/rfc5250>.
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[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
February 2016, <https://www.rfc-editor.org/info/rfc7770>.
12.2. Informative References
[I-D.li-dynamic-flooding]
Li, T. and P. Psenak, "Dynamic Flooding on Dense Graphs",
draft-li-dynamic-flooding-05 (work in progress), June
2018.
[I-D.shen-isis-spine-leaf-ext]
Shen, N., Ginsberg, L., and S. Thyamagundalu, "IS-IS
Routing for Spine-Leaf Topology", draft-shen-isis-spine-
leaf-ext-06 (work in progress), June 2018.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.
Appendix A. Algorithms to Build Flooding Topology
There are many algorithms to build a flooding topology. A simple and
efficient one is briefed below.
o Select a node R according to a rule such as the node with the
biggest/smallest node ID;
o Build a tree using R as root of the tree (details below); and then
o Connect k (k>=0) leaves to the tree to have a flooding topology
(details follow).
A.1. Algorithms to Build Tree without Considering Others
An algorithm for building a tree from node R as root starts with a
candidate queue Cq containing R and an empty flooding topology Ft:
1. Remove the first node A from Cq and add A into Ft
2. If Cq is empty, then return with Ft
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3. Suppose that node Xi (i = 1, 2, ..., n) is connected to node A
and not in Ft and X1, X2, ..., Xn are in a special order. For
example, X1, X2, ..., Xn are ordered by the cost of the link
between A and Xi. The cost of the link between A and Xi is less
than the cost of the link between A and Xj (j = i + 1). If two
costs are the same, Xi's ID is less than Xj's ID. In another
example, X1, X2, ..., Xn are ordered by their IDs. If they are
not ordered, then make them in the order.
4. Add Xi (i = 1, 2, ..., n) into the end of Cq, goto step 1.
Another algorithm for building a tree from node R as root starts with
a candidate queue Cq containing R and an empty flooding topology Ft:
1. Remove the first node A from Cq and add A into Ft
2. If Cq is empty, then return with Ft
3. Suppose that node Xi (i = 1, 2, ..., n) is connected to node A
and not in Ft and X1, X2, ..., Xn are in a special order. For
example, X1, X2, ..., Xn are ordered by the cost of the link
between A and Xi. The cost of the link between A and Xi is less
than the cost of the link between A and Xj (j = i + 1). If two
costs are the same, Xi's ID is less than Xj's ID. In another
example, X1, X2, ..., Xn are ordered by their IDs. If they are
not ordered, then make them in the order.
4. Add Xi (i = 1, 2, ..., n) into the front of Cq and goto step 1.
A third algorithm for building a tree from node R as root starts with
a candidate list Cq containing R associated with cost 0 and an empty
flooding topology Ft:
1. Remove the first node A from Cq and add A into Ft
2. If all the nodes are on Ft, then return with Ft
3. Suppose that node A is associated with a cost Ca which is the
cost from root R to node A, node Xi (i = 1, 2, ..., n) is
connected to node A and not in Ft and the cost of the link
between A and Xi is LCi (i=1, 2, ..., n). Compute Ci = Ca + LCi,
check if Xi is in Cq and if Cxi (cost from R to Xi) < Ci. If Xi
is not in Cq, then add Xi with cost Ci into Cq; If Xi is in Cq,
then If Cxi > Ci then replace Xi with cost Cxi by Xi with Ci in
Cq; If Cxi == Ci then add Xi with cost Ci into Cq.
4. Make sure Cq is in a special order. Suppose that Ai (i=1, 2,
..., m) are the nodes in Cq, Cai is the cost associated with Ai,
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and IDi is the ID of Ai. One order is that for any k = 1, 2,
..., m-1, Cak < Caj (j = k+1) or Cak = Caj and IDk < IDj. Goto
step 1.
A.2. Algorithms to Build Tree Considering Others
An algorithm for building a tree from node R as root with
consideration of others's support for flooding reduction starts with
a candidate queue Cq containing R associated with previous hop PH=0
and an empty flooding topology Ft:
1. Remove the first node A that supports flooding reduction from the
candidate queue Cq if there is such a node A; otherwise (i.e., if
there is not such node A in Cq), then remove the first node A
from Cq. Add A into the flooding topology Ft.
2. If Cq is empty or all nodes are on Ft, then return with Ft
3. Suppose that node Xi (i = 1, 2, ..., n) is connected to node A
and not in the flooding topology Ft and X1, X2, ..., Xn are in a
special order considering whether some of them that support
flooding reduction (. For example, X1, X2, ..., Xn are ordered
by the cost of the link between A and Xi. The cost of the link
between A and Xi is less than that of the link between A and Xj
(j = i + 1). If two costs are the same, Xi's ID is less than
Xj's ID. The cost of a link is redefined such that 1) the cost
of a link between A and Xi both support flooding reduction is
much less than the cost of any link between A and Xk where Xk
with F=0; 2) the real metric of a link between A and Xi and the
real metric of a link between A and Xk are used as their costs
for determining the order of Xi and Xk if they all (i.e., A, Xi
and Xk) support flooding reduction or none of Xi and Xk support
flooding reduction.
4. Add Xi (i = 1, 2, ..., n) associated with previous hop PH=A into
the end of the candidate queue Cq, and goto step 1.
Another algorithm for building a tree from node R as root with
consideration of others' support for flooding reduction starts with a
candidate queue Cq containing R associated with previous hop PH=0 and
an empty flooding topology Ft:
1. Remove the first node A that supports flooding reduction from the
candidate queue Cq if there is such a node A; otherwise (i.e., if
there is not such node A in Cq), then remove the first node A
from Cq. Add A into the flooding topology Ft.
2. If Cq is empty or all nodes are on Ft, then return with Ft.
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3. Suppose that node Xi (i = 1, 2, ..., n) is connected to node A
and not in the flooding topology Ft and X1, X2, ..., Xn are in a
special order considering whether some of them support flooding
reduction. For example, X1, X2, ..., Xn are ordered by the cost
of the link between A and Xi. The cost of the link between A and
Xi is less than the cost of the link between A and Xj (j = i +
1). If two costs are the same, Xi's ID is less than Xj's ID.
The cost of a link is redefined such that 1) the cost of a link
between A and Xi both support flooding reduction is much less
than the cost of any link between A and Xk where Xk does not
support flooding reduction; 2) the real metric of a link between
A and Xi and the real metric of a link between A and Xk are used
as their costs for determining the order of Xi and Xk if they all
(i.e., A, Xi and Xk) support flooding reduction or none of Xi and
Xk supports flooding reduction.
4. Add Xi (i = 1, 2, ..., n) associated with previous hop PH=A into
the front of the candidate queue Cq, and goto step 1.
A third algorithm for building a tree from node R as root with
consideration of others' support for flooding reduction (using flag F
= 1 for support, and F = 0 for not support in the following) starts
with a candidate list Cq containing R associated with low order cost
Lc=0, high order cost Hc=0 and previous hop ID PH=0, and an empty
flooding topology Ft:
1. Remove the first node A from Cq and add A into Ft.
2. If all the nodes are on Ft, then return with Ft
3. Suppose that node A is associated with a cost Ca which is the
cost from root R to node A, node Xi (i = 1, 2, ..., n) is
connected to node A and not in Ft and the cost of the link
between A and Xi is LCi (i=1, 2, ..., n). Compute Ci = Ca + LCi,
check if Xi is in Cq and if Cxi (cost from R to Xi) < Ci. If Xi
is not in Cq, then add Xi with cost Ci into Cq; If Xi is in Cq,
then If Cxi > Ci then replace Xi with cost Cxi by Xi with Ci in
Cq; If Cxi == Ci then add Xi with cost Ci into Cq.
4. Suppose that node A is associated with a low order cost LCa which
is the low order cost from root R to node A and a high order cost
HCa which is the high order cost from R to A, node Xi (i = 1, 2,
..., n) is connected to node A and not in the flooding topology
Ft and the real cost of the link between A and Xi is Ci (i=1, 2,
..., n). Compute LCxi and HCxi: LCxi = LCa + Ci if both A and Xi
have flag F set to one, otherwise LCxi = LCa HCxi = HCa + Ci if A
or Xi does not have flag F set to one, otherwise HCxi = HCa If Xi
is not in Cq, then add Xi associated with LCxi, HCxi and PH = A
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into Cq; If Xi associated with LCxi' and HCxi' and PHxi' is in
Cq, then If HCxi' > HCxi then replace Xi with HCxi', LCxi' and
PHxi' by Xi with HCxi, LCxi and PH=A in Cq; otherwise (i.e.,
HCxi' == HCxi) if LCxi' > LCxi , then replace Xi with HCxi',
LCxi' and PHxi' by Xi with HCxi, LCxi and PH=A in Cq; otherwise
(i.e., HCxi' == HCxi and LCxi' == LCxi) if PHxi' > PH, then
replace Xi with HCxi', LCxi' and PHxi' by Xi with HCxi, LCxi and
PH=A in Cq.
5. Make sure Cq is in a special order. Suppose that Ai (i=1, 2,
..., m) are the nodes in Cq, HCai and LCai are low order cost and
high order cost associated with Ai, and IDi is the ID of Ai. One
order is that for any k = 1, 2, ..., m-1, HCak < HCaj (j = k+1)
or HCak = HCaj and LCak < LCaj or HCak = HCaj and LCak = LCaj and
IDk < IDj. Goto step 1.
A.3. Connecting Leaves
Suppose that we have a flooding topology Ft built by one of the
algorithms described above. Ft is like a tree. We may connect k (k
>=0) leaves to the tree to have a enhanced flooding topology with
more connectivity.
Suppose that there are m (0 < m) leaves directly connected to a node
X on the flooding topology Ft. Select k (k <= m) leaves through
using a deterministic algorithm or rule. One algorithm or rule is to
select k leaves that have smaller or larger IDs (i.e., the IDs of
these k leaves are smaller/bigger than the IDs of the other leaves
directly connected to node X). Since every node has a unique ID,
selecting k leaves with smaller or larger IDs is deterministic.
If k = 1, the leaf selected has the smallest/largest node ID among
the IDs of all the leaves directly connected to node X.
For a selected leaf L directly connected to a node N in the flooding
topology Ft, select a connection/adjacency to another node from node
L in Ft through using a deterministic algorithm or rule.
Suppose that leaf node L is directly connected to nodes Ni (i =
1,2,...,s) in the flooding topology Ft via adjacencies and node Ni is
not node N, IDi is the ID of node Ni, and Hi (i = 1,2,...,s) is the
number of hops from node L to node Ni in the flooding topology Ft.
One Algorithm or rule is to select the connection to node Nj (1 <= j
<= s) such that Hj is the largest among H1, H2, ..., Hs. If there is
another node Na ( 1 <= a <= s) and Hj = Ha, then select the one with
smaller (or larger) node ID. That is that if Hj == Ha and IDj < IDa
then select the connection to Nj for selecting the one with smaller
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Internet-Draft Flooding Reduction September 2018
node ID (or if Hj == Ha and IDj < IDa then select the connection to
Na for selecting the one with larger node ID).
Suppose that the number of connections in total between leaves
selected and the nodes in the flooding topology Ft to be added is
NLc. We may have a limit to NLc.
Authors' Addresses
Huaimo Chen
Huawei Technologies
Email: huaimo.chen@huawei.com
Dean Cheng
Huawei Technologies
Email: dean.cheng@huawei.com
Mehmet Toy
Verizon
USA
Email: mehmet.toy@verizon.com
Yi Yang
IBM
Cary, NC
United States of America
Email: yyietf@gmail.com
Chen, et al. Expires March 24, 2019 [Page 42]
