MTU site to site on Router 1800

Unanswered Question
Oct 10th, 2007


It seems that standard MTU value is set to 1399 when configured router over web SCM.

Get problem on my windows AD and need to increase this to 1492 over the VPN tunnel.

How can I do that? is it on tunnel or card interface inside/outside

Kind please HELP ;)

I have this problem too.
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Paolo Bevilacqua Wed, 10/10/2007 - 14:38

Which kind of tunnel is that exactly?

if you want to find the MTU by yourself, proceed as following:

- remove all metu and ip mtu statements from involved interfaces.

- do "ping x.y.z.k df size to the other end of tunnel, progressively inreasing or decreasing size untile the largest possible is found.

- Configure this value as "ip mtu" on the tunnel interface.

jonas_sth Wed, 10/10/2007 - 22:54

I configured my routers with SDM tool and like the help function says that default value is 1400.


Enter the largest amount of data, in bytes, that should be allowed in a packet travelling through the tunnel.

SDM Default: 1400

How should I change that to 1492 or 1500 by telenet?

Paolo Bevilacqua Thu, 10/11/2007 - 04:57

Conf term

interface XXX

mtu YYY

or, for a tunnel interface

interface tunnel X

ip mtu Y

exit, wr mem

Hope this helps, please rate post if it does!


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