My server is operating properly.
Suddenly, my server is inaccesible via ssh and http. (The only open ports in the firewall.)
All eth0 configuration is static, no DHCP.
Everything is configured properly in /etc/network/interfaces.
ethtool is configured to force 100baseT full duplex, as is the gateway - autoneg is off.
ifconfig shows zero errors, zero dropped packets, zero overruns, and zero collisions.
My server responds to pings sent from other networks. (Which must go through the gateway?)
route shows everything configured properly.
My server receives no response from pings sent to the gateway.
My server gets responses from other machines on the local network.
After receiving ping responses from other local machines, it can then get a response from the gateway, http operates properly and so does ssh. I didn't restart or reconfigure the network in any way, the only commands used were
ping (in the order indicated above) to bring server access back.
See this question for more background information. (I implemented the suggested solution provided, but to no avail.)
Any ideas? This problem has been ongoing for weeks, and I'm at a complete loss...