Les,
Thanks a lot for the detailed explanation.
Section 3 of RFC 5120 says " A router MUST announce the MT IS TLV when there is at least one adjacency on the interface that belongs to this MT, otherwise it MAY announce the MT IS TLV of an adjacency for a given MT if this interface participates in the LAN".
The statement implies that on interfaces which are not LANs, the LSP sent out need not contain information about the topologies in which the adjacency does not participate.
So, this seems to suggest that in your example,IS reachability for MT ID 10 need not be sent on adjacency BC and IS reachability for MT ID 20 should not be sent on adjacency AB.
Regards
Leela
-----Original Message-----
From: Les Ginsberg (ginsberg) [mailto:ginsberg at cisco.com]
Sent: Wednesday, November 04, 2009 2:47 PM
To: Leela Janaki P; isis-wg at ietf.org
Subject: RE: [Isis-wg] Carrying MT info in MT-ISIS
Leela -
On a given link a router is configured to support a set of topologies. When it forms an adjacency on that link, only the topologies which are supported by both routers (i.e. the intersection of the set of supported topologies advertised by each router in its IIHs) can be used in MT Intermediate Systems TLV (222).
Consider the following simple example:
A----B----C
A supports topologies 0,10
B supports topologies 0, 10, 20 on all links
C supports topologies 0, 20
B forms an adjacency with A. The intersection of the set of supported topologies is (0,10).
B forms adjacency with C. The intersection of the set of supported topologies is (0,20).
In its LSPs B will advertise:
TLV 22
Neighbor A
Neighbor C
TLV 222
MTID 10 Neighbor A
MTID 20 Neighbor C
This information will be flooded on all links.
LSPs are not generated differently based on which link they are flooded on. And the set of LSPs generated contain information about reachability to all supported topologies.
Les
-----Original Message-----
From: isis-wg-bounces at ietf.org [mailto:isis-wg-bounces at ietf.org] On
Behalf Of Leela Janaki P
Sent: Tuesday, November 03, 2009 11:46 PM
To: 'isis-wg at ietf.org'
Subject: [Isis-wg] Carrying MT info in MT-ISIS
Hello,
I have a question regarding carrying Multi-topology TLVs in ISIS.
For point to point interfaces, RFC5120 says that MT IS TLV in an LSP
MUST contain the reachability of the topology only when the adjacency
is enabled for that topology. This seems to imply that if an IS
contains multiple adjacencies , each with different topologies , then
the LSPs sent out on each of them will be different. I just want to
confirm if this is the desired behaviour. Alternately is it permitted
for an IS to send a single LSP containing information of all topologies
supported by the IS or to send out a separate LSP one for each
topology.
Thanks,
Leela
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