Re: [trill] seeking help to understand a line from TRILL-ESADI draft

Donald Eastlake <d3e3e3@gmail.com> Tue, 17 July 2012 19:26 UTC

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From: Donald Eastlake <d3e3e3@gmail.com>
Date: Tue, 17 Jul 2012 15:27:16 -0400
Message-ID: <CAF4+nEHPAfXjJxohOry0JdafjFDi=KemLJQh+ZYzuzi03cjwLw@mail.gmail.com>
To: Swet kumar <swet.kumar@ipinfusion.com>
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Cc: "trill@ietf.org" <trill@ietf.org>
Subject: Re: [trill] seeking help to understand a line from TRILL-ESADI draft
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Hi Swet,

On Tue, Jul 17, 2012 at 5:59 AM, Swet kumar <swet.kumar@ipinfusion.com> wrote:
> Hi Authors,
>
>
> I am not able to understand the meaning of the following line in this draft:
> http://tools.ietf.org/pdf/draft-ietf-trill-esadi-00.pdf

Thanks for reviewing this document. It was just recently posted as a
WG document and I think it does need some more work.

> “For robustness, if an ESADI instance has two or more ESADI neighbors
>
>    and is not DRB and it receives no ESADI-CSNP PDUs for at least the
>
>    CSNP Time (see Section 6.1) of the DRB, it MAY transmit an ESADI-
>
>    CSNP.”

Do you really no understand what the sentence says? Or is it that you
don't understand what the reason is for this behavior?

The idea is that if the DRB on an ESADI virtual link is being flakey
or the virtual link is broken then, to maintain LSP synchronization,
it would be good for some other TRILL switch on that ESADI virtual
link to occasionally send a CSNP. The multi-hop ESADI pseudo-link is
inherently somewhat less reliable that a link between adjacent TRILL
switches. (You might think this could result in a flurry of CSNPs but
note that, due to the jitter in the IS-IS reliable flooding mechanism,
if there were several non-DRB TRILL switches on the link, as soon as
one sends a CSNP it will inhibit the others for a while.)

Anyway, although it doesn't make much difference. It should probably
say "one" instead of "two" in the text and it should not just be that
it has not received a CSNP but that it has not received or sent a
CSNP. So, I think the wording should be changes to:

   "For robustness, if an ESADI instance has one or more ESADI neighbors
   and is not DRB and it does not receive or send an ESADI-CSNP PDU
   for at least the CSNP Time (see Section 6.1) of the DRB, it MAY
   transmit an ESADI-CSNP."

Thanks,
Donald
=============================
 Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
 155 Beaver Street, Milford, MA 01757 USA
 d3e3e3@gmail.com

> This line is a part of section 4.1 (Sending of ESADI PDUs) on page number
> 12.
>
> Please explain me what this line tries to convey.
>
>
> Regards,
>
> Swet