I have configured nat and pat on the pix 515, every so often the connection is lost to the internet, leaving it for 25/30 minutes it starts working again.
This doesn't sound like a address translation problem. Even if translation times out, it takes less than a few seconds to setup a new one. You might wanna check your uplink (or uplink devices)
I have a similar problem on PIX 506 but i have doubts on my router routes , as soon as i switch off the router & start again the connection comes on again. It happens almost every 2 hours.
I think I have overcome the problem, I missed out on one variable.. The public IP addresses being used for the Global range did not have reverse DNS entries.
So i am hopeful that this will cure the problem. maybe you should also check..
