Cisco Nexus MTU issue

Hi All,

Got a weird issue which I am after some help on. I have two Cisco N5K switches in location A, let's call them A1 and A2, connected to a Catalyst stack in location B (B1 and B2).

There is a single link connecting the two, from a trunk port on A2 to a trunk port on B2.

I created SVIs on each switch on the same vlan, testing ping connectivity between all the switches, and all is successful. However, if I increase the packet size above 250 bytes, I get some weird behaviour, here are the results:

Switch A1 to A2 (300bytes+) - success Switch A1 to B1 (300bytes+) - failure Switch A1 to B2 (300bytes+) - failure Switch A2 to B1 (300bytes+) - success Switch A2 to B2 (300bytes+) - success

The thing that is baffling me is that for traffic to get from A1 to B1, it has to pass through A2, yet A2 is able to ping both A1 and B1 up to 1450 with no issues.

Pinging back the other way from the other side of the link I encounter the same issue. Everything is able to ping fine up to around 250 bytes, then after this point everything works fine except pings to A1, and any clients connected to A1.

I checked MTU sizes with a sh run all, and all interfaces are set at 1500.

I'm a bit stumped as to where to go from here, suggestions greatly appreciated.