Re: MTU problems with GRE tunnels

[Jose Manuel de Arce <josema () ibernet es>]

        Hello

        We had similar problems and we used 1524 bytes mtu's in serials interfaces
in the cisco config:

# int ser 0
# mtu 1524

        I am also interested in extra info regarding this gre problem, but for a
quick fix try playing with mtu size over serials interfaces.

        Kind regards

                        Josema

At 09:53 AM 6/5/98 +0100, philip bridge wrote:
> I'm experiencing problems with fragmentation due to Cisco GRE tunnel
> overhead: the way I understand it, the MTU if a GRE tunnel will always be
> less than the MTU of the underlying IP cloud (in our case 1500 bytes) due
> to the IP encapsulation overhead. So 1500 byte packets attempting to
> traverse the tunnel will be fragmented, or dropped if the DF bit is set, in
> which case an ICMP message is send back to the originating host