Changing MTU on IPSEC interface only? Possible?

[jdamnation]

We have moved to a new firewall system, replacing an old Snapgear unit with a pair of Pfsense boxes. All in all (despite a few weird things) we're very happy.

However, we suspect we have some MTU fragging going on with the VPN link. For some reason, we didn't have this issue with the Snapgear unit, and we're running the same IPSEC configuration. We have a Hifn card for IPSEC offload.

We still have a Snapgear at the other end, so I was thinking perhaps this was part of the problem. We are able to manually adjust the MTU of the IPSEC interface on the Snapgear - but we can't seen to do this with pfsense. We can adjust the MTU of the WAN interface, but then almost all of the WAN traffic on this setup is HTTPS - and we are worried about slowing that down by reducing the packet sizes.

So what we really want to do - is reduce the MTU on the IPSEC interface, but not the WAN interface.

Possible?

JD