Re: [Lsr] Comments on draft-white-lsr-distoptflood-03

[Antoni Przygienda <[e-mail]>]

No Announce: thanks, we agree

Well, given LSP flooding is unrelible as well it seems no better and no worse if we RTX. The PSNP bits will be hanging there and I guess we have to put it on a RTX mechanism or we rely on CSNP. Good comment.

Yes, the PSNPs are _in addition_ so yes, I agree also here we can fall back on those. I kind of prefer those since it doesn’t change protocol behavior further than it already does by sending the additional PSNP

Thanks


  *   Tony

From: Les Ginsberg (ginsberg) <[e-mail]>
Date: Friday, 29 July 2022 at 15:08
To: Antoni Przygienda <[e-mail]>, [e-mail] <[e-mail]>
Subject: Comments on draft-white-lsr-distoptflood-03
[External Email. Be cautious of content]


Tony (and everyone) -

Following up on the brief discussion about this draft at today's WG meeting...

I withdraw the comment regarding having to announce use of the algorithm. After rereading I agree this is not necessary.

Regarding my second comment about the use of PSNPs as a recovery mechanism in cases where topology changes temporarily compromise the optimized flooding...the draft says in Section 2.3

<snip>
o  Set a short timer; the default should be one second

   o  When the timer expires, send Partial Sequence Number Packet (PSNP)
      of all LSPs that have not been reflooded during the timer runtime
      to all neighbors unless an up-to-date PSNP or CSNP has been
      already received from the neighbor
<end snip>

Given that PSNPs are unreliable, how can you guarantee that the neighbor has received the PSNP(s) required by the most recent set of LSP updates which were NOT flooded to that neighbor?

The traditional way of closing this gap is to send periodic CSNPs on interfaces where flooding may have been suppressed. In this way you guarantee the reliability of the update process.
The recovery time may be a bit slower as sending CSNPs every second is excessive - but I do not see how you guarantee reliability without periodic transmissions.

Or do you mean to say send the PSNP once IN ADDITION to periodic CSNPs?? This would allow quicker recovery in most cases while using a slower periodic timer for the CSNPs as protection in case the PSNP was lost.

   Les


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