[nsp] ospf over tunnels

[Tony Tauber]

On Wed, 11 Sep 2002, Mark Kent wrote:

> Date: Wed, 11 Sep 2002 10:43:20 -0700 (PDT)
>
> I've got remote site 1 on a DS3 with MTU 4470
> and remote site 2 on a fastethernet with MTU 1500.
>
> I have a GRE tunnel between them, with a cisco7206vxr
> on each end, 12.0(21)S on each router.
>
> I can't run ospf between the two because of this:
>
> Sep 11 10:35:46: OSPF: Rcv DBD from x.y.z.w on Tunnel0 seq 0x8C9 opt 0x42 flag 0x7 len 32  mtu 4446 state EXSTART
> Sep 11 10:35:46: OSPF: Nbr x.y.z.w has larger interface MTU
>
> Any suggestions?
>
> If I change the MTU on my DS3 to 1500 then what happens
> to the 1514 MTU on the tunnel?
>
> Thanks,
> -mark

I believe the tunnel interface inherits from its parent.
However, you can override by applying "ip mtu 1500" to the tunnel
interface itself.  I've had this problem and fixed it that way.

Tony