Unexpected Firewall Log output

[nikkilocke]

I have a new pfSense installation, running in a VMWare VM.
My LAN interface is 192.168.100.10, connected to a router at 192.168.100.1 which routes to subnets 192.168.3.0/24 and 192.168.1.0/24.
I have static routes for these subnets in pfSense with 192.168.100.1 as the gateway.
My WAN interface is 192.168.2.10, connected to an ADSL NAT router at 192.168.2.5.
I have NAT on the pfSense too.

I am getting repeated log entries of the form:
WAN 192.168.2.10:43624 (ip address censored):110 TCP:F

Why should I be getting these?
They are presumably relics of valid NATted sessions from a machine on my LAN which periodically checks my POP mailbox (which is at that address).

[kpa]

http://doc.pfsense.org/index.php/Logs_show_%22blocked%22_for_traffic_from_a_legitimate_connection,_why%3F

[nikkilocke]

Thanks for that. I take it there is no way to avoid these appearing in the logs?

[jimp]

@nikkilocke:

Thanks for that. I take it there is no way to avoid these appearing in the logs?

No, because although they are related to a connection that just closed, there is no way for the filter to know this since the state is already gone. It's sort of a catch-22: If they were part of the state, the filter would know about it, and they wouldn't be blocked. If they aren't a part of the state, they get blocked, but there is no way to not log them because it no longer thinks they are valid.

[nikkilocke]

Is there any way of slowing down the discard of the state, so that the FIN packet has time to arrive before the state is gone?

[jimp]

You could try changing the firewall optimization to 'conservative' but I'm not sure if that will affect this particular type.