Ethernet CAT5 Cheat Sheet

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Pins are numbered consecutively in order (1 to 8) when looking at the outside of a jack in "standard position" (facing the hole with contacts up above it), and in reverse order (8 to 1) when looking at the outside of a connector (facing the end with the contacts up). (The difference is because you have to rotate the connector 180 degrees around the vertical axis in order to plug it in to the jack.)

Wire color coding and pin assignments for 10Base-T and 100Base-Tx:

Pair Strand Pin Signal
Orange white/orange 1 TX+
orange 2 TX-
Green white/green 3 RX+
green 6 RX-
Blue white/blue 4 Not used
blue 5 Not used
Brown white/brown 7 Not used
brown 8 Not used

[The color code was cribbed from the "cheat sheet" sticker on the inside of a jack; I am assuming these pin assignments are standard. Several manufacturers of Category 5 (Cat5) cable use these same colors, so at least the color code is conventional. -- rgr, 6-Jul-01.] [But see the RJ45 page, which swaps green and orange. -- rgr, 15-Jun-04.]

So for crimping a connector, put the colors in the following order, from left to right looking into the back of the connector (the cable end, with the contacts up):

Pin Straight   Crossover
1 white/orange   white/green
2 orange   green
3 white/green   white/orange
4 white/blue   white/blue
5 blue   blue
6 green   orange
7 white/brown   white/brown
8 brown   brown
Note that for a crossover cable you want to install exactly one connector with a crossover, and the other one normally ("straight"); if both connectors are crossed over, the result is equivalent to a straight cable. [Note that crossover cables are not always needed with modern equipment; many recent hubs and switches autodetect how the lines are being used, and compensate accordingly. -- rgr, 1-Jul-03.]

Bob Rogers <>