MTU mismatch on one link

Paul Vinciguerra pvinci at
Fri Aug 31 13:52:09 UTC 2012

You need to raise your MTU above that on the other side and do a ping size sweep.  Unlike at Layer-3 when you can use set a DF bit and get back an ICMP error, at Layer-2 when you exceed the far side's MTU, the packets are silently dropped.

Paul Vinciguerra
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-----Original Message-----
From: Tom Taylor [mailto:tom.taylor.stds at] 
Sent: Friday, August 31, 2012 9:30 AM
To: NANOG list
Subject: MTU mismatch on one link

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

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