PMTU and Broken Servers

Mikael Abrahamsson swmike at
Thu May 8 17:04:18 UTC 2003

On Thu, 8 May 2003, Leo Bicknell wrote:

> Could you define newer?  My limited testing with 12.0S and 12.2something
> shows both returing MTU can't be set on a tunnel interface.

You cannot change the MTU of the tunnel, but you can change the "ip mtu" 
of the tunnel. I've done this on 7200 and 1600 that are running IOSes that 
are at least a year old. The feature is at least 2-3 years old, because 
that's the first time I encountered it.

The router will do re-assembly on the tunnel level to be able to transfer 
a 1500 byte sized IP packet non-fragmented.

Mikael Abrahamsson    email: swmike at

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