[155961] in North American Network Operators' Group
Re: MTU mismatch on one link
daemon@ATHENA.MIT.EDU (John Neiberger)
Fri Aug 31 14:04:48 2012
In-Reply-To: <5040BC58.7060808@gmail.com>
From: John Neiberger <jneiberger@gmail.com>
Date: Fri, 31 Aug 2012 12:03:20 -0600
To: Tom Taylor <tom.taylor.stds@gmail.com>
Cc: NANOG list <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Fri, Aug 31, 2012 at 7:30 AM, Tom Taylor <tom.taylor.stds@gmail.com> wrote:
> Has anyone run into a situation where the MTU at one end of a link was
> configured differently from the MTU at the other end? How did you catch it?
>
> In general, do you see any need for a debugging tool to be standardized to
> find such mismatches?
>
> Tom Taylor
>
I've seen several cases where BGP would not come back up after a link
flap. In every case, this was when we had 7600 on one end and a CRS
on the other and we had the MTU configured exactly the same on each
side. The MTU value on the CRS should be 14 bytes higher than an IOS
device because the XR device includes the Ethernet header size.
Whenever I see a BGP session that does not come back up after a link
flap, I immediate check MTU size on both sides.
John
