Re: [Idr] [Fwd: I-D Action:draft-chen-rfc4893bis-00.txt]

[Paul Jakma <paul at jakma.org>]

On Tue, 27 Jan 2009, John G. Scudder wrote:

> On Jan 27, 2009, at 12:52 PM, Rob Shakir wrote:
> > We feel that the general behaviour on an error should be the withdrawal
> > of the path, as discarding the attribute is equivalent in effect to
> > discarding part of the AS_PATH and may cause loops. Take for example the
> > case when an BGP speaker in a 32bit AS receiving an invalid AS4_PATH
> > attribute. With the AS4_PATH unreadable and therefore discarded the BGP
> > speaker cannot know if its AS number was in the path. The only loop free
> > options are:
>
> While intuitively obvious, this isn't correct.  As long as there's no 
> corresponding damage to the AS_PATH, the loop free property is preserved. 
> Here's the argument:

That's an argument as to why it doesn't break down completely if 
everything else is working in spec, which is indeed a nice property. 
I'm still puzzled as how this is an argument to not restore AS-path 
checking back to its full-strength.

- It's not robust if two OLD speakers in a cycle each remove the
  other's ASN, with the remaining speakers on the cycle all being
  NEW.

- It's not robust in a cycle of all NEW speakers where one session,
  for some reason, is both OLD and causes the AS4_PATH to be ignored.

I really don't see what benefits there are to leave loop-detection 
degraded in this way in a mixed world.

But hey..

regards,
--
Paul Jakma	paul at clubi.ie	paul at jakma.org	Key ID: 64A2FF6A
Fortune:
Extremism in the defense of liberty is no vice... moderation in the pursuit
of justice is no virtue.
		-- Barry Goldwater
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