A couple of times now, an ASA5520 - Software Version 7.1(2) stops passing traffic (no changes made to the ASA for weeks). The interfaces are up/up (one is connected to a 3750 (full/1000Mbps) and the other to a LES100 circuit (full/100Mbps) and no errors are on the interfaces. I can ping from the ASA GUI tools option to remote devices, but cannot ping or telnet through the ASA (normally I can). There are duplicate SYN packet messages which implies to me that the packets are being re-transmitted with no response (indicates a physical connectivity issue - powered off the LES100 circuit but still a problem). A power off/on fixes the issue, but a reload doesn't.
Can someone give me some pointers where I can start to look the next time this occurs?