3Com XLPCI manual Troubleshooting Hubs with Crossover Cable, Crossover cable

C-2APPENDIX 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.

1Connect 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.

2To 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:

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	Straight-through				Crossover
	10BASE-T cable				10BASE-T cable
1		1	TD+ 1		1	TD+
2		2	TD	2	2	TD
3		3	RD+ 3		3	RD+
4		4		4	4
5		5	RD	5	5	RD
6		6		6	6
7		7		7	7
8		8		8	8

Figure C-1Straight-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.