nanog mailing list archives

RE: Heads up: Long AS-sets announced in the next few days


From: "David Schwartz" <davids () webmaster com>
Date: Thu, 3 Mar 2005 17:26:41 -0800



So, given these considerations, is everyone announcing an AS-set
announcing "routes that falsely claim to have passed through another
autonymous system"?

    Yes. From RFC1771:

Ok, so if everyone announcing an AS-set is announcing "routes that
falsely claim to have passed through another autonymous system", and you
are saying this shouldn't be done, then why aren't you complaining with
everyone who is announcing an AS-set?

        I never said that this shouldn't be done. I said it shouldn't be done
without the consent of the owners of the ASes you wish to include. In
addition, the things I don't complain about don't constitute a defense to
the things I do complain about.

[Quote of section 5.1.2 almost in its entirety]

    So you are violating RFC1771, plain and simple. To then go
and cite one
small section of RFC1771 in your defense is hypocritical.

You quote Section 5.1.2, but you don't mention that if you follow
Section 5.1.2 to the letter there is no way that an AS-path may contain
an AS-set. To summarize the whole of section 5.1.2, the various cases are:

Propagating a route learned from an UPDATE message:

  a) To another router in same AS: don't modify AS-path
  b) To a neighboring AS:
     1. Path starts with AS_SEQUENCE: prepend own ASn
     2. Path starts with AS_SET: prepend new AS_SEQUENCE with own AS in it

Originating a route:

   a) To neighboring AS: announce own ASn as only element in path
   b) To another router in same AS: announce empty AS-path

If you follow this to the letter, you must rule out both prepending "(In
this case, the AS number of the originating speaker's autonomous system
will be the only entry in the AS_PATH attribute)" and any form of
AS-set, since there is no way, following these rules, that an AS-set may
enter the AS-path in the first place.

        Section 9.2.4.2 documents how an AS-set can enter the AS-path as part of
aggregating routes. As far as I can tell, the use of AS-sets is permitted
only to aggregate routes.

If we are violating this section, then everyone else announcing an
AS-set, and - at least the way I read it - anyone doing prepending, is
doing so too. But nobody is suggesting that these things
shouldn't be done.

        Lovely straw man. I complained about the lack of *consent* and you talk
about people prepending their *own* AS numbers? Are you suggesting they lack
their own consent?!

        DS



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