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Troubleshooting a Network Connection 137
Troubleshooting Hubs
A crossover cable can be used to identify the type of failure
when hub performance or connectivity is in question.
To use a crossover cable:
1 Connect a file server and a client PC back-to-back
with a crossover cable to verify that the NIC and
network operating system are properly configured.
2 To make a crossover cable, connect TD+ to RD+ and
TD– to RD–.
The cable performs the crossover that is usually performed
by the hub.
Cabling Pinouts
The following illustration compares the cabling pinouts for
straight-through and crossover cables.
If the file server and client PC function together as a small
network, then either the existing cabling or the hub is
failing.
When a crossover cable is used, the LED on the NIC functions
differently than it would under normal operating conditions.
For example, with a correct crossover connection, the LED
lights, whereas with a straight-through connection, the LED
does not light. If you make a crossover cable and the polarity
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Straight-through
10BASE-T cable
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Crossover
10BASE-T cable
TD+
RD+ RD+
TD+
TD– TD–
RD– RD–