[nsp] ospf over tunnels

[Luciano Salata]

Mark,

What about ip ospf mtu-ignore (under interface configuration)  ?

Regards,

Luciano

-----Mensaje original-----
De: cisco-nsp-admin@puck.nether.net
[mailto:cisco-nsp-admin@puck.nether.net]En nombre de Mark Kent
Enviado el: Miércoles, 11 de Septiembre de 2002 02:43 p.m.
Para: cisco-nsp@puck.nether.net
Asunto: [nsp] ospf over tunnels


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

Cisco (http://www.cisco.com/warp/public/104/12.html) basically
says "tough luck", and contains this gem

   Since the problem is caused by mismatched MTUs, the solution is to
   change either router's MTU to match the neighbor's MTU. Note that
   Cisco IOS doesn't support changing the physical MTU on a LAN interface
   (such as Ethernet or Token Ring). When the problem occurs between a
   Cisco router and another vendor's router over LAN media, adjust the
   MTU on the OTHER VENDOR'S ROUTER.

(upper-case is my editing).

Any suggestions?

If I change the MTU on my DS3 to 1500 then what happens
to the 1514 MTU on the tunnel?

Thanks,
-mark
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