MTU mismatch on one link

Fri Aug 31 13:59:11 UTC 2012

On Fri, 31 Aug 2012, Tom Taylor 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?

Some routing protocols (OSPF comes to mind) will complain loudly and 
generally refuse to come up if configured on a link with mismatched MTUs.

As far as a debugging tool, I don't know if one is specifically needed for 
that, but another thing to watch out for is in cases where you use 
something like an Ethernet transport from a metro provider to get between 
two locations, make absolutely certain that you find out from the provider 
how the circuit is engineered, including what the MTU is for the link, and 
how they encapsulate your traffic to transport it across their network 
(MPLS, QinQ, etc).

jms