My server is running Ubuntu 10.04 and is connected by ethernet to a router/modem device. The problem is that it's basically ignoring incoming connections. So I can't SSH into it or access the webserver. It wont even accept connections from other machines within the network.
However, it can make outbound connections fine. When it starts up it successfully sends me the startup email (connects to gmail SMTP servers etc). It can also perform DNS requests and get the response fine, after trying "dig". ethtool and ifconfig confirm that the server is connected and has the usual internal IP address.
The strange thing is that on the routers control panel, there are no signs of the server being connected at all. The server does not connect using DHCP, but manually defined settings. I've double checked the config and everything is fine (as it should be - I haven't changed anything).
This is a pain to troubleshoot, so could anyone give me any pointers on what the problem may be? I'm having to read commands out over the phone because I can't just SSH in and play around.