AS path question.

Holmes,David A dholmes at mwdh2o.com
Wed Nov 10 15:35:49 CST 2010


Some use AS prepends, not for traffic engineering, as ISPs often
override AS prepends with private peering (communities/local pref
settings), but for the simple purpose of making advertised prefixes
stand out amongst a welter of BGP routes. 

-----Original Message-----
From: Greg Whynott [mailto:Greg.Whynott at oicr.on.ca] 
Sent: Wednesday, November 10, 2010 12:22 PM
To: nanog at nanog.org list
Subject: AS path question.



Recently I adjusted the maxas-limit option on our router,    logs
started reporting routes being refused because the AS path is to long.
seems to work as expected.

when I looked at the logs I was a bit confused at what i was looking
at...   why is it there are multiple AS's in the path that appear to be
the same AS?  I expected an AS path comprised of mostly unique ASs.

instead of this:

476330: Nov 10 14:55:07.247 EDT: %BGP-6-ASPATH: Long AS path 549 26677
6939 21011 43022 43022 43022 43022 43022 47359 47359 47359 47359 47359
47359 47359 47359 received from isp router: More than configured
MAXAS-LIMIT



i expected it would look more like:

476330: Nov 10 14:55:07.247 EDT: %BGP-6-ASPATH: Long AS path 549 26677
6939 21011 43022  47359 received from ... .. .




thanks for your time again,
greg






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