HOW-TO - Ethernet Cables

Parts: You'll need several feet of CAT 5/5e/6 cable, RJ45 ends and an RJ45 crimper to complete this. You'll also need a nice cut-off plier. A wire striper and a cable tester are greatly helpful aswell.

Cable: First, start off with good quality cable, it has to be UTP (Unshielded Twisted Pair) Category 5/5e/6 cable, don't skimp on this (Shielded works too, but isn't necessary). Bulk cable comes in many types, there are 2 basic categories, solid and braided cable. Braided cable tends to work better in "patch" applications for desktop use. It is more flexible and resiliant than solid cable and easier to work with, but really meant for shorter lengths. Solid cable is meant for longer runs in a fixed position. Plenum rated cable should/must be used whenever the cable travels through an air circulation space. For example, above a false celing or below a raised floor.
Your likely going to want braided type cable.

Ethernet Cables: Now, on to the cables. There are two basic cables. A straight through cable, which is used to connect to a hub or switch, and a cross-over cable used to operate in a peer-to-peer fashion without a hub/switch. Gigabit copper interfaces can actually cross and un-cross a cable automatically as needed, really quite nice. Since you are making your own cables, I will assume you understand which cable you need.

Standard, Straight-Through Wiring (both ends are the same):

RJ45 Pin #	Wire Color	Wire Diagram	Signal*
1	White/Orange		Transmit+
2	Orange		Transmit-
3	White/Green		Receive+
4	Blue		Unused
5	White/Blue		Unused
6	Green		Receive-
7	White/Brown		Unused
8	Brown		Unused

Table 1 - Straight-Through Cable Pinout
* For 10Base-T and 100Base-TX, 1000Base-T uses all pairs

Cross-Over Cable:

RJ45 Pin # (END 1)	Wire Color	Diagram End #1
1	White/Orange
2	Orange
3	White/Green
4	Blue
5	White/Blue
6	Green
7	White/Brown
8	Brown

RJ45 Pin # (END 2)	Wire Color	Diagram End #2
1	White/Green
2	Green
3	White/Orange
4	Blue
5	White/Blue
6	Orange
7	White/Brown
8	Brown

If you look closely, you will noticed that the green and orange pairs are swapped or crossed, these are the transmit and receive pairs.

Procedure: 1.  To create the cable, strip off about 2 inches of the cable sheath. When you get to the second side, cut the wire to length and make sure it is more than long enough for your needs. Remember, an end to end connection should extend at least 1m (3ft) and not more than 100m (~328ft). Yes, there is a minimum, its little known, little referred to and not usually important, but I have seen cases where short cables caused problems. The longer the cable becomes the more it may affect performance, usually it is a gradual decrease in speed and increase in latency. When uplinking between (cascading) hubs/switches, you usually need a very short cable, less than 1m, check the device's specifications.
2.  Next untwist the pairs, don't untwist them beyond what you have exposed, the more untwisted cable you have the worse the problems you can run into.
3.  Now you want to align the colored wires according to the diagrams above. When nicely aligned, hold them in line together and trim them all to the same length, about 1/2" to 3/4" left exposed from the sheath. And then you want to insert them into the RJ45 end and make sure each wire is fully inserted to the front of the RJ45 end and in the correct order. The sheath of the cable should extend into the RJ45 end by about 1/2" and will be held in place by the crimp. Crimp the end with the crimper tool and once again verify the wires ended up the right order and that the wires extend to the front of the RJ45 end and make good contact with the metal contacts in the RJ45 end. If you have a cable tester, put it to use, and verify the proper connectivity of your newly made cable.
4.  That should be it, if your cable doesn't turn out, look closely at each end and see if you can find the problem. Usually a wire ended up in the wrong place or more commonly, one of the wires didn't extend to the front of the RJ45 connector and is making no, or poor contact. If you see a mistake or problem, cut the end off and start again.