Subject: [rbridge] Regarding 'The Tree Identifiers Sub-TLV'

From: keshav karedla <[email-masked]>
Date: Fri, 30 Dec 2011 20:14:36 +0530

Hi Authors,

It is mentioned in RC 6326 that

"The tree identifiers (TREE-RT-IDs) sub-TLV is an ordered list of

nicknames. When originated by the IS that has the highest priority

tree root, it lists the distribution trees that the other ISs are

required to compute as specified in Section 4.5 of [RFC6325]. If

this information is spread across multiple sub-TLVs, the starting

tree number is used to allow the ordered lists to be correctly

concatenated."

If the RBridge has the highest priority tree root for one of its nickname
among the campus, it will give the distribution trees computed/ordered by
it for the campus in this sub-TLV to tell other RBridges these are the
trees computed for campus, but what other RBridges send in this TLV ?

As per my understanding other RBridges send nothing or they may send their
configured nicknames in their configured order. Am I right ?

Please clarify me.

Regards,

Keshav
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From: Radia Perlman <[email-masked]>
Date: Fri, 30 Dec 2011 12:23:45 -0800

I believe that RBs other than the highest priority one don't send this TLV,
or if they do (perhaps because they don't know they aren't the highest
priority RB yet because they haven't seen the higher priority RB's LSP),
then that TLV is ignored by the other RBs.

Radia

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From: Donald Eastlake <[email-masked]>
Date: Fri, 30 Dec 2011 16:21:03 -0500

Hi,

> then that TLV is ignored by the other RBs.

Generally I would say that's right although for robustness you might
want some number of the RBridges that are highest priority to be a
tree root to send appropriate versions of the Tree Identifiers sub-TLV
to minimize changes in case the highest priority RBridge fails or
something like that.

Thanks,
Donald
=============================
 Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
 155 Beaver Street, Milford, MA 01757 USA
 [email-masked]

>> among the campus, it will give the distribution trees computed/ordered by it
>> for the campus in this sub-TLV to tell other RBridges these are the trees
>> computed for campus, but what other RBridges send in this TLV ?
>>

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From: Radia Perlman <[email-masked]>
Date: Fri, 30 Dec 2011 14:40:04 -0800

So Donald and I aren't really disagreeing.  He's saying that even though
this TLV would be ignored if sent by an RB other than the highest priority
RB, it might be useful for RB2 (perhaps one of the highest priority RBs,
but not currently the highest priority RB), to include this TLV in its
LSP, so that if the highest priority RB dies, the tree information would
still be available in the LSP database.  Otherwise, if R1 (the highest
priority RB) died, the other RBs wouldn't know what the trees were, and
would have to wait for R2 to notice R1 died, and reissue its LSP with the
TLV.

The spec doesn't say which RBs other than the highest priority should
include this TLV.  It doesn't take up much space, so it wouldn't be
unreasonable for all RBs to include it, or perhaps there should be a
configuration parameter as to whether an RB should include it or not, or
perhaps a configuration parameter configured at RB2 saying that RB2 should
include this TLV if RB2 is one of the k highest priority RBs (e.g., k=5).

But at any rate, if RBs other than the highest priority RB include this
TLV, their value will be ignored by the other RBs.

Radia