[c-nsp] MTU size difference and OSPF

[sthaug at nethelp.no]

> The problem arises when I have to fit the GigaEthernet interface of the 7206 to accomodate packets with bigger than 1500 due to MPLS. On the main interface,
> I have to use this command
> 
> #interface Gi0/1
> #mtu 1520
> 
> Without this command, I cannot key in the following commands in Gi0/1.1
> 
> #mpls mtu 1520
> 
> This allows me to send packets with the MPLS labels as well as keep the normal IP MTU to 1500.
> 
> However at this point, if the OSPF between the Cat6509 and the 7206 is broken for any reason, it will never reestablish. It will always loop between EXSTART/DOWN because of the MTU difference. 

Use "ip mtu 1500" on your Gi0/1.1 to match the IP MTUs on the respective
routers.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no