Question : SBS2008 stops being able to initiate network connections

This has now happened twice, both times I have had limited time to fault-find the problem as the client wanted the server fixed, and a reboot has worked both times so far. This has happened twice so far, two weeks apart.

The server loses the ability to initiate a connection, either to itself or to an external computer. If the connection is initiated from outside, eg PPTP or RDP, it works fine, but it is unable, for example, to look up Active Directory from Exchange (so no external mail is received, but internal mail is fine).

The server can ping all the way out to the internet, so the problem must be a higher level than ICMP. Windows Firewall is enabled by default, but disabling it did not solve the problem. SBS2007 does not have ISA. The Antivirus is Trend, but does not have the firewall enabled.

Nothing in the event log indicates any problem. Once it happens the errors are all symptoms, not a root cause. As an example I could not telnet to port 25 on localhost, but could telnet to it from another computer.

At the moment my only theory is that something in SBS2008 / Trend is mistaking legitimate traffic for malicious activity and closing outgoing ports, but by this point I had run out of time and had to restart the server.

Answer : SBS2008 stops being able to initiate network connections

Server still up, so still looking like AV client was problem.