ANSWER:

You need to look at the server’s logs to determine what is going on. Start in /var/log/messages.

Next, you need to sample traffic on the server to watch how it is seeing network communication at the wire level. Start by using Wireshark.

After those investigative measures, you can begin the real fun of tracking down the specific trouble. However, before those simple things have been done, there’s not much else to go on.

Remember that the rules of troubleshooting, regardless of the discipline, are always:

1. Gather Data
2. Gather Data
3. Gather Data

Oh yeah, and something about making a hypothesis and then falsifying it. =)

by WesleyDavid from http://serverfault.com/questions/382825