Optimal MTU size for Samba connections

[FortiGateAdmin]

Hello,

I have two sites connected to two FortiGates via a 1Gbit line (symmetrical) from the provider.
Unfortunately, there is a performance problem when accessing Windows shares and I wanted to ask if you can tell me from experience the optimal MTU and TCP MSS value.

Thanks!

[Golle]

1500 byte is the default and recommended MTU. If you start increasing the MTU then you need to make sure the full path supports this increased MTU, otherwise you will have issues.

Recommended MSS is MTU - 40 for ipv4, so with a 1500-byte MTU you want 1460 MSS.