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C-2 APPENDIX C: TROUBLESHOOTING NETWORK CONNECTION PROBLEMS
Troubleshooting Hubs with Crossover Cable
A crossover cable can be used to identify the type of failure
when hub performance or connectivity is in question.
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. Figure C-1 shows the pinouts for the
crossover cable:
.
Figure C-1 Straight-through and Crossover Cable Pinouts
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
is mismatched (that is, TD+ to RD– instead of TD+ to RD+),
the LED blinks.
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Straight-through
10BASE-T cable
Crossover
10BASE-T cable
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TD+
RD+
TD
RD
TD+
RD+
TD
RD