Illegal header length in BGP error

Mills, Charles cmills at
Tue Feb 24 15:53:56 UTC 2009

I ran into exactly the same thing during a code upgrade a few weeks ago.

I wrote it off as a bug in BGP and backed off the code until a new release was out.  I was also running 12.4(22)T
On an NPE-G2.


-----Original Message-----
From: Renaud RAKOTOMALALA [mailto:renaud at] 
Sent: Tuesday, February 24, 2009 10:49 AM
To: Matthew Huff; 'nanog at'
Subject: Re: Illegal header length in BGP error

Hello Matthew,

We changed the motherboard from cisco one of our from 7206VXR (NPE-G1) 
to 7206VXR (NPE-G2).

Due to incompability with the IOS 12.3(4r)T3 we upgraded this IOS to 
12.4(12.2r)T. At the end we've got the same problem as you between one 
of our 7200 in 12.3 and the new one in 12.4 ....

We solved the problem by upgrading the cisco withe the IOS from 
12.4(12.2r) to 12.4(4)XD10 and the BGP session came back alive ....

So now everything work fine between our 7200 (IOS 12.3) and the other 
7200 in IOS 12.4(4)XD10

I hope it could help you ...


Matthew Huff a écrit :
> 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)?

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