A follow up question to that posted by a user on May 3rd, 2009.
On my 2621XM that uses DHCP to obtain an IP addresss from my ISP, I have a reflexive acl that allows all inside-originated traffic out and responses back in.
I do successfully obtain an IP address and all connectivity from inside works well - for about 20 minutes. Ater 20 minutes or so (the time can vary), I lose communication to the internet.
The router still has the IP address but I can no longer reach the ISP or any where else. As simple shut/no shut of the outside interface restores communication. I don't see any errors or messages in the log file. I don't see anything in debug of ip packets to indicate why it would stop functioning. I've increased the ACL aging value to 1 hour (3600 seconds).
It is not an issue with the ISP as when I use my Linksys rather than the 2621 I don't lose connectivity.