OSPF mtu size

[dheeraj7]

Hello

I have a customer in a vprn on a 7750 router, who uses ospf to exchange routing information. OSPF is not coming up unless the mtu size is set to 1500 on the customer router. Is there a way to tell the 7750SR PE router to ignore the mtu size on the PE?

[didigno]

You need to MTU in order to establish the OSPF adjacency, the MTU value must match between the 2 sites. I do not think that there is a workaround for it.

[mivens]

Another option is setting config>router>ospf>area>interface>mtu on the 7750 to match the customer router.

[dheeraj7]

Thanks didigno and mivens for your insights. The problems clears when the mtu size is set both on the customer router and the PE router. I did try to set the mtu size on PE side to match that of the CPE, in this case it was 4470 for SHDSL interface, but it did not work. The reason i was looking for a PE side solution, is that we have customers currently on Huawei routers which we are migrating to Alcatel. Huawei ignores mtu size by default but Alcatel does not and apparently the only solution is to configure same mtu size on both ends.

Cheers

[mivens]

If you haven't done so already, you might want to check from a debug on the 7750 what the MTU being advertised by the CPE in the OSPF DBD packets is when you don't have it explicitly set. The full 4470 bytes might not be available to OSPF.