Subject: RE: [Isis-wg] Derek's proposal for MTU discovery in IS-IS

From: Les Ginsberg <[email-masked]>
Date: Mon, 2 Jul 2001 13:05:21 -0700

> 
> How does this compare with the proposal which was originated 
> in the Sonet 
> Interoperability Forum and is being incorporated in ISO/IEC 
> 10589 second 
> edition?
> 
> 
> 

The SIF proposal is concerned with advertising originatingLSPBufferSize. The
TLV appears in an LSP and has area wide(L1) or domain-wide(L2) implications.

The MTU discovery proposal TLV appears in an IIH and has immediate
significance only between neighbors on a link. It is certainly true that
there is a relationship between originatingLSPBufferSize and link MTU size
in that the MTU size on ALL links on which LSPs will be propagated must be
>= originatingLSPBufferSize. In that sense the two proposals complement each
other - though the use of padding appropriately applied also serves this
purpose.

For those who are interested, the SIF proposal was posted to the list back
in 1998 and (amazingly) is still available at:

   ftp.juniper.net:pub/isis/lspsize.PDF

It is allegedly still available on the SIF website but I found that link to
be stale.

It should also be mentioned that a minor change to the proposal above has
been made to resolve the TLV conflict with
draft-ietf-isis-wg-snp-checksum-01.txt. The two TLVs (12 and 13) mentioned
in the document have been combined into a single TLV(14). The determination
of whether the size being advertised is L1 or L2 is determined by the LSP
type in which the TLV is found.

(I have been waiting for formal commitment for this change to be
incorporated into the latest draft of ISO 10589 before announcement - guess
I have done it now.)

  Les
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