Step 1: Verify the Status of the Physical Network

The first item to check is the physical network. The majority of today's networking hardware provides status indicators that you can use to assess the state of the various network links (for example, 10-BASE-T Hubs use LEDs). Always check these links for any signs of problems with the physical network such as excessive re-transmissions, link Integrity mismatches, and jabber conditions.

Even in cases in which only a single client is affected, never assume that is it not a bad cable connection. For a single client it is easy to check to determine whether the problem occurs regardless of which server the client tries to use.

If a client cannot "see" anything on a network that is otherwise functioning without incident, then it is safe to assume that the problem is related to that client's network configuration. If however, that same client can see other nodes on the network but cannot connect to a particular server, then the network path to that server, the server itself, or the account being used by that client are likely candidates for trouble.

There are several third-party products available that you can use to monitor the health of the physical network. It is worthwhile to check network traffic periodically with one of these devices to see whether there are problems occurring with the physical network.