MTU mismatch on one link

John Neiberger jneiberger at
Fri Aug 31 18:03:20 UTC 2012

On Fri, Aug 31, 2012 at 7:30 AM, Tom Taylor <tom.taylor.stds at> 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.


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