Network Working Group Sina Mirtorabi
Internet Draft Abhay Roy
Document: draft-mirtorabi-ospfv3-tag-00.txt Cisco Systems
Expiration Date: August 2004 February 2004
Route tags in OSPFv3
draft-mirtorabi-ospfv3-tag-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Abstract
This document describes a mechanism to carry a route tag in OSPFv3.
Currently only external LSA can carry a tag. This document propose a
method to carry tags for intra and inter area prefixes.
1. Introduction
[Ref 1] defines tag for OSPFv2 and the usage of it carried with a
prefix. This document propose a solution for OSPFv3 [Ref 2] by
defining new LSA's to carry tag. The new LSA's will not carry any
prefix to duplicate the generation of prefix within the domain but
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simply associate a tag with list of Link State IDs corresponding to
LSA's that carry prefixes.
2. Intra-area-tag-LSA
We define a new LSA called intra-area-tag-LSA to carry tag within an
OSPFv3 area. The flooding scope of the LSA is area wide and the
Unknown bit (U bit) is set.
LSA function code LS Type Description
----------------------------------------------------
12 0xA00C Intra-area-tag-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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age |1|0|1| 12 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| LSA body |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The contents of LSA is constructed as sets of tag block defines
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rsrv |E| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Rsrv
Reserved field, it should be set to 0 and ignored in reception
E bit
Extended tag bit, when is set the tag will be defined as a 64
bit value, otherwise it is defined as 32 bit value
Length
The length of the tag block excluding the first four byte
(Rsrv+ E + length field)
Tag
A configurable value set by the user
Link State ID
Link state ID of the intra-area-prefix-lsa that carries prefixes
to be tagged
Note that a given Link State ID corresponds to the fragment of
intra-area-prefix-lsa which contains prefixes which have a common
tag (see section 3).
3. Generation of intra-area-tag-LSA
When a router is configured to tag its intra-area prefix, it MUST
originate intra-area-prefix-LSA in such a way that all prefixes
within a fragment have the same tag value. This is needed since Tag
LSA associate a tag to a LSA identified by its Link State ID which
may carry many prefixes.
A router configured to tag intra-area prefixes, generates
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intra-area-tag-LSA corresponding to Link State IDs advertised in
its intra-area-prefix-LSA.
Note that intra-area-tag-LSA should be regenerated only when there is
a change in tag value or the Link State ID list has changed. In other
words if intra-area-prefix-lsa is regenerated due to a change of
metric or prefix reachability, there is no need to regenerate
intra-area-tag-LSA.
4. Multi-access link consideration
In a multi-access link, Designated Router (DR) is in charge of
generating intra-area-prefix-lsa on behalf of the link. In order to
tag prefixes on the multi-access link the designated router SHOULD
be tag capable and the tag needs to be configured on the DR/BDR.
Note that the DR will have to generate multiple
intra-area-prefix-lsas such that all prefixes within a fragment have
the same tag value. DR will also generate intra-area-tag-LSA
corresponding to Link State IDs advertised in it's
intra-area-prefix-lsa.
5. Inter-area-tag-LSA
We define a new lsa called Inter-area-tag-LSA to carry tag between
OSPFv3 areas. The flooding scope of the LSA is area wide and the
Unknown bit (U bit) is set. This LSA is generated by ABRs.
LSA function code LS Type Description
----------------------------------------------------
13 0xA00D Inter-area-Tag-LSA
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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| 13 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| LSA body |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The contents of LSA is constructed as sets of tag block defines
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rsrv |E| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Rsrv
Reserved field, it should be set to 0 and ignored in reception
E bit
Extended tag bit, when is set the tag will be defined as a 64
bit value, otherwise it is defined as 32 bit value
Length
The length of the tag block excluding the first four byte
(Rsrv + E + length field)
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Tag
A configurable value set by the user
Link State ID
Link state ID of the Inter-area-prefix-lsa that carries the
prefix to be tagged
Note that each Link State ID correspond to a unique prefix in
Inter-area-prefix-lsa, however each tag block could carry a list of
Link State ID.
6. Generation of Inter-area-tag-LSA
An ABR that generates inter-area-prefix-LSA is in charge of tagging
inter-area prefixes. This is done by generating inter-area-tag-LSA
that corresponds to inter-area-prefix-LSA Link State IDs generated
by the ABR. The same rule for processing and generating
inter-area-prefix-LSA applies to processing and generating
Inter-area-tag-LSA.
7. Backward compatibility
This document does not introduce any backward compatibility issues.
The new LSA is simply ignored by non-capable routers.
8. Deployment consideration
Tag capable router could be introduced gradually without any
interoperability problem. It should be noted that in order to tag
inter-area prefixes, the ABRs need to be tag capable so that the
tags can be propagated through multiple areas.
9. Security Considerations
The technique described in this document does not introduce any new
security issues into OSPFv3.
10. References
[Ref1] Dec, Psenak, Sturgess, "A Proposal for a Tag Value field in
OSPF", draft-dec-ospf-tags-00.txt
[Ref2] R. Coltun, D. Ferguson and J. Moy, "OSPF for IPv6",
RFC 2740, December 1999.
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