MTU across switches

Hey guys,

So I’m going to link two backbone switches up, each contains about 35 computers and a few servers. The switches are both Dell FTOS but years apart so the operating system is like 9.3 vs 10.5.

I’d like to link them via 10 gig and set the MTU size to 9000 on each perspective interface.

However on one switch after I set the MTU to 9000 it says ip MTU 8968 and layer 2 9000 and on the other switch after I set the interface to 9000 it says ip mtu 8982 while 9000 on layer 2. So a 14 bit difference between the two switches.

I’ve successfully linked the switches up but I got a LLDP configuration mismatch on the interface in the logs, however, everything works.

So I guess my question is : do I want 9000 and 9000 at layer 2 but be off by 14 at layer 3. Or do I want to match 9000 to 90014 at layer 2 to match 8082 to 8082 at layer three?

This is just an access port link, no trunking.

Also I’ve never really tested two switches linked at 9000MTU before while the rest of the network is at 1500. Does it make a big performance difference?

Also I cannot upgrade the OS of the old switch incase anyone wanted to recommend that. Because probably if I did that by default MTU would be the exact same but I can’t because the old switch is in production and I just need this to work for a few months, then the old switch is getting replaced.

Also the same mtu mismatch happens at the default 1500 setting as well.