OSPF MTU Size

[#1]

I am trying to route over an interface VPN between 2 fortigates. The VPN is up and passing traffic with static routes. I have enabled OSPF and all set up correctly. The problem is the routers are complaing that the MTU size is invalid. How can I adjust this. If I change the MTU on my PPPoE connection at one end to something other than 1500 it changes back all the time when I connect. I have tried adjusting the MTU on the VPN interface in the CLI and still keep getting the same message. Any ideas anyone ?

[thors_hammer]

Dear graemef, try changing the MTU size of the OSPF. You can do this via CLI and the commands: conf router ospf conf ospf-interface edit " <your VPN-OSPF-interface-name>" *like configured via webgui set mtu xxxx end end Keep in mind to change the MTU size at both ends of the tunnel... Regards, Thorsten

[HA]

Hello, Rather than changing the MTU size on the physical/tunnel interface, you should configure the following command under the OSPF tunnel interface : mtu-ignore enable. In fact, by default, OSPF checks if the the MTU is the same before creating the adjaceny (FULL state). In your case, I think that it should in stuck in EXCHANGE state... REM: Need to be enabled on BOTH side !! Regards, Hedi

[HA]

Sorry, The state sould be in Exstart (and not Exchange) state in your case... Regards, Hedi

[#5]

Many thanks for the help. For some reason disabling the MTU check still returned the error, but maybe I didn' t leave it long enough. A combination of both suggestions has worked beautifully. Thanks