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If all users of the network are experiencing the problem, it could be related to a different device, such as a server that everyone accesses. Or, a main router or hub could be down, making network transmissions impossible.

Additionally, if the network has WAN connections, you can determine if a network problem is related to the WAN connection by checking to see if stations on both sides can communicate. If they can, the problem isn’t related to the WAN. If they can’t communicate, you must check everything between the sending station and the receiving one, including the WAN hardware. Usually, the WAN devices have built-in diagnostics that can indicate whether the WAN link is functioning correctly to help you determine if the fault is related to the WAN link or to the hardware involved.

Cabling Issues

After you determine whether the problem is related to the whole network, to a single segment, or to a single workstation, you must determine whether the problem is related to network cabling. First, check to see if the cables are properly connected to the correct port. More than once, I’ve seen a wall phone cable plugged into a modem in the In jack.

Additionally, patch cables from workstation to wall jack can and do go bad, especially if they get moved or tripped over often. This problem is often characterized by connection problems. If you test the NIC and there is no link light (discussed earlier in this chapter), the problem could be related to a bad patch cable.

It is also possible to have a cabling problem in the walls where the cabling wasn’t installed correctly. If a network cable was run over a fluorescent light, for example, the workstation attached to that cable might have problems only when the lights are on. The problem is that the fluorescent lights produce a large amount of EMI and can disrupt communications in that cable. This kind of problem may manifest itself only at times when most lights need to be on.

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