In the middle of the day I lost internet access, turned out there was a problem on the Serial Interface. It showed that Serial0 is up, line protocol is down. I tried to shutdown the port and then do a no sh but it stay up for only a few seconds before it drops again. I tried rebooting the router and called my ISP who said my circuit was fine, and I could see that they were in it because the test lights were changing back and forth. I also conferenced in Cisco, and they too were stumped. The Cisco tech and ISP tech compared all their stats and information and everything matched up as it should. I am using a Cisco 2620 with Frame Relay. I have changed all my cables as well. Does anyone have any ideas? Could it be the CSU/DSU card?