OSPF MTU question with FEX Jumbo MTU

[davidjohnredfern]

Hi,

I have an OSPF MTU question as we have a need to enable Jumbo Frames on our Nexus 7K FEX modules which will apply L2 MTU of 9216 to all FEX ports. 

We have devices directly connected to the FEX (ASA's and ISR routers) peering OSPF with the Nexus 7K using an MTU of 1500 (SVI's and/or L3 FEX ports).  After we enable Jumbo frames the 'IP MTU' of the peering interfaces will still match at 1500, but the 'L2 MTU' of the ports will be mismatched. 

In this scenario, does OSPF only require the 'IP MTU' to match to work properly?  Or could the L2 MTU mismatch cause issues?

[mlund]

Hi

As long as the L2 mtu is higher than the L3 mtu, there will be no issues regarding OSPF establishment.

/Mikael

[Sebastian Fernandez]

L2 MTU don't need to match as long it is can support the L3 MTU. As long there is un-fragmented connectivity with the L3 MTU OSPF should be fine. 

-Sebastian