I'm using 2 PIX-525's with VACs to establish a VPN between 2 cities using our internet provider (SURFnet) and Gb-ethernet links.
At random moments users who have an estabilished TCP connection to a MS Terminal server (RDP) are disconnected (2-3 times a day). They can reconnect directly but is seems that the standing TCP connections are broken. I configured al timers en keep-alives quite basic/default.
Some of the earlier versions of PIX OS used to send out a reset on seeing ip header with a bad checksum, thus resulting in sessions getting dropped at times. I believe this problem of reset TCP connections was fixed in PIX OS version 5.1.something. I guess the problem is most likely that you are running one of these older OS versions.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...