Episode 03, Segment 02 of 04Ethernet Cables (continued)
However, there’s a second kind of cable that’s less common, but you will run into it once in a while. This is called a “cross-over” cable, and in a cross-over cable, the colors are reversed. The pairs twist over each other. There are times when switching from a cross-over cable to a straight-through cable will make or break your network. So you’ll really need to be able to identify which is which. Sometimes, cross-over cables are made in an identifying color, but you cannot rely on that. Sometimes they have a tag or a printed label that identifies them as cross-over, but you cannot rely on that either, and if you can’t either a printed label or a tag that makes it obvious, then you have to look at the color-coded wires on the end, just closely enough to determine whether they are straight-through, or whether they have been modified.
(Click above image for enlarged version)
If you’ve got good eyesight and compare the ends of the cross-over cable like this, you can see that the colors crossing over is pretty obvious. They’re obviously not both wired the same. Once I make that determination, I like to take a permanent magic marker and write “crossover” right on the wire for my future reference. We’ll talk about the situations in which you might use a cross-over cable versus a straight-through cable in a moment, but before we get to that, there’s another important variable that we need to learn about.
Episode 03, Segment 3 of 4