I have one customer I installed a Digital Watchdog DVR and opened a port (not 80, duh!). At some point in time, the DVR could not be viewed remotely (after 6-12 months). I went to the site, logged onto the router and discovered the port was no longer open. I reopened the port again and so far the problem has not reoccurred. This was a ATT U Verse router, but I don't remember which model. It's been behaving for at least a year but I know that sooner or later I will have to roll another truck.