Strange lost connection

[PaoloA]

Hello all,

I have a new 2.1 box with a strange problem: sometimes, without an apparent reason, it stops to accept traffic from a server in DMZ (OPT1).
The pfsense don't replay to server's ping and the server don't replay to pfsense's ping.
But if I ping another box in the same net, both replay and works as expected, so it don't seems to be a problem in one of the nics.
After a random time, the problem vanished without having done nothing.
No useful info in the logs (for what I can understand).
The pfsense is a clean install with no packages installed
The server is a OpenVZ VM (DNS server and sawdog (a simple watchdog: http://fossies.org/linux/privat/sawdog-2.4.tar.gz:a/sawdog-2.4/README)), with really low traffic, that works without problem if I switch it to another gateway/firewall (the old pfsense 2.0.3 that I want replace).
DMZ is configured as NAT with simple Port Forward. No bridging.

Any hints to solve/debug the problem?

Thanks, P.