lots of prepends

Thu Feb 19 21:24:27 UTC 2009

Just seen that here too:

Feb 19 16:20:35: %BGP-6-ASPATH: Long AS path 8001 8928 20912 20912 20912
20912 20912 20912 20912 20912 20912 20912 20912 20912 20912 20912 20912
20912 20912 20912 20912 20912 20912 20912 20912 20912 20912 20912 20912
20912 20912 20912 20912 20912 20912 20912 20912 20912 20912 20912 20912
20912 20912 20912 20912 20912 20912 20912 20912 20912 20912 20912 20912
20912 20912 20912 20912 20912 20912 20912 20912 20912 20912 20912 20912
20912 20912 20912 20912 20912 20912 20912 20912 20912 20912 20912 20912
20912 20912 20912 received from 207.99.64.25: More than configured
MAXAS-LIMIT

Our AS path limit is 100 which is way too high in my opinion but
regardless I was trying to figure out any logic in this.... I can
remember prepending one of our upstreams 4X at one point thinking that
was a bit nuts .... thankfully we don't prepend anyone these days....

Paul

-----Original Message-----
From: Mikael Abrahamsson [mailto:swmike at swm.pp.se] 
Sent: Thursday, February 19, 2009 4:21 PM
To: nanog at nanog.org
Subject: lots of prepends

Today 85.119.176.0/21 was announced by AS20912 with 177 prepends. I 
noticed 20912 modulo 256 is 176. AS47868 modulo 256 is 252 which matches

this mondays prepend-incident.

So, what router OS will put 20912 into a byte and thus end up with 176
in 
something like "set as-path prepend last-as <no of prepends>" ? It needs

to be fixed.

Has anyone noticed any ill effects with IOS and using "bgp max-as"? Will

it just drop any prefixes with long as-paths and no other ill
operational 
effects?

-- 
Mikael Abrahamsson    email: swmike at swm.pp.se

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