AS_PATH length and route selection (WAS: Strange BGP announcement)

Tue Nov 17 23:28:54 UTC 1998

At 06:03 PM 11/17/98 -0500, Vijay Gill wrote:

>You appear to have misunderstood the problem.  The issue has nothing to do
>with route selection, or are you talking about FastPath(TM, Pat Pending)
>here?

Cute, Vijay.  Really cute.

Of course, if everyone had only licenced it, we wouldn't have this problem
now, would we? :p

>The issue is that an invalid as-path attribute was injected from
>somewhere. The cisco as-path sanity check code failed to pick it up.

[SNIP]

I have not misunderstood the problem, you have misunderstood my response.
Someone posted that the routers should follow the RFC.  I was commenting
that you should be careful what you wish for.  If we magically made all
routers strictly conform to the RFC instantly, it would have solved this
particular problem, but it would have caused *much* larger problems for the
'Net at large.

I was also hoping to start a debate by those more knowledgeable than I
about the ... wisdom of intentionally removing what is currently far and
away the most used metric for route selection from the next version of BGP;
namely: AS_PATH length.  (At least I was under the impression that AS_PATH
length was the used more than all other metrics combined for route
selection in the backbone.)  RFC1771 does not list AS_PATH length as a
selection criteria - but at least RFC1771 does not specifically forbid use
of AS_PATH length, as the draft for the next version does.

Or perhaps I'm just misinformed.  I have not actually read the draft for
BGP 4+ (or whatever they're calling it now).  This is second hand
information, but I consider it to be from a very reliable source (even if
he doesn't like ciscos ;).  I am also not saying removal of this metric is
a gigantic mistake, but my thought process to date leads me to tentatively
believe it would be ... suboptimal.  However, the people writing the spec
obviously know more about it than I do, perhaps I've overlooked something.

So, would anyone care to discuss (from an operational POV) what removing
AS_PATH length from the BGP route selection algorithm will do to the Internet?

>/vijay

TTFN,
patrick

P.S.  Before anyone goes off on me, I once again *agree* that the least
cisco could do is deal with malformed announcements and the errors they
generate properly.  There are just other parts of the RFC with which I'm
not so sure I agree.

I Am Not An Isp
www.ianai.net
"Think of it as evolution in action." - Niven & Pournelle