Illegal header length in BGP error

Matthew Huff mhuff at
Tue Feb 24 14:48:46 UTC 2009

One of our upstream providers flapped this morning, and since then they are
sending corrupted BPG data. I'm running 12.4(22)T on cisco 7200s. I'm
getting no BGP errors from that providers and the number of routes and basic
sanity check looks okay. However, when it tries to redistribute the bgp
routes via iBGP to our other board routers, we get:

003372: Feb 24 09:17:13.963 EST: %BGP-5-ADJCHANGE: neighbor x.x.x.x Down BGP
Notification sent
003373: Feb 24 09:17:13.963 EST: %BGP-3-NOTIFICATION: sent to neighbor
x.x.x.x 1/2 (illegal header length) 2 bytes     

All routes have identical hardware and IOS versions. My google and cisco
search fu leads me to the AS path length bug, but the interesting thing is
that since we have "bgp maxas-limit 75" configured and a recent IOS, we
haven't had the problem before when other people were reporting issues. I've
also looked at the path mtu issue, and although we haven't had a problem
before I disabled bgp mtu path discovery, but have the same issues.

Anyone seeing something like this today, and or does anyone have a
suggestion on finding out more specific info (which as path for example so I
can filter it)?

Matthew Huff       | One Manhattanville Rd
OTA Management LLC | Purchase, NY 10577  | Phone: 914-460-4039
aim: matthewbhuff  | Fax:   914-460-4139
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