1

I need to make a ethernet crossover cable to connect two devices together. Anyone know the process to make one from scratch?

quack quixote
  • 42,186
  • 14
  • 105
  • 129
Axxmasterr
  • 7,858
  • 7
  • 41
  • 60
  • 2
    Google would be a much better place to ask this question: http://www.google.com/search?q=how+do+i+wire+a+crossover+cable – raven Jul 30 '09 at 02:04
  • 8
    The point of superuser.com, as well as the other related websites is to become THE place for answers to computer questions. If someone "google's" it they should be pointed here. – Kenneth Cochran Jul 30 '09 at 02:25
  • 3
    Is the one of the main reasons for superuser.com's existence is to capture knowledge around generalized areas. You could comment on every question here, on stackoverflow.com, & serverfault.com that we should just "Google it", but then we wouldn't have the community here and the collective knowledge that is being built. – SitWalkStand Jul 30 '09 at 02:27
  • 1
    I can't see making this site "*the* place for answers to *all* computer questions". That seems like an unrealistic goal. Is this site attempting to replace google.com? If it is, I apologize, if not, this question is quite easily answered there. – raven Jul 30 '09 at 02:44
  • 1
    @Raven: Would you make the same sort of suggestion to MS TechNet or the sites which warehouse the results of court decisions and judicial precedents? Those communities could use Google too. There is a reason why they choose to do otherwise. – Axxmasterr Jul 30 '09 at 02:49
  • 1
    There was a similar discussion in Podcast 58: http://blog.stackoverflow.com/2009/06/podcast-58/. I also think it's noise, but apparently Joel finds these valid. – hyperslug Jul 30 '09 at 03:29
  • Except in unusual circumstances the best value is probably to buy a crossover cable from a reputable supplier, especially if it is for high-speed use. Whether you make it yourself or buy one do make it visibly distinct from your usual cables (e.g. different colour flex, different style of connectors) – mas Jul 30 '09 at 12:10

3 Answers3

7

Before you start, if one of the devices is Gbit-capable the send and receive lines are negotiated automatically and thus no crossover is needed.

Ozan
  • 784
  • 5
  • 9
  • 3
    just about any switch made in the last 5 years or so will auto-sense whether or not the cable is crossed over. – Jeff Leonard Jul 30 '09 at 02:35
  • *> if one of the devices is Gbit-capable the send and receive lines are negotiated automatically*   So then you can connect a 10/100 NIC to a GbE NIC with a straight-through patch-cord? What if the auto-negotiation setting is not on? Can you damage a NIC by using a patch-cord instead of crossover (e.g., between two 10/100 NICs)? Can a crossover damage two GbE NICs? – Synetech Jul 22 '12 at 23:43
5

Check out this tutorial. Here are some images from it for context:

enter image description here

Note that the TX (transmitter) pins are connected to corresponding RX (receiver) pins, plus to plus and minus to minus. And that you must use a crossover cable to connect units with identical interfaces. If you use a straight-through cable, one of the two units must, in effect, perform the cross-over function.

enter image description here

Note that pins 4, 5, 7, and 8 and the blue and brown pairs are not used in either standard. Quite contrary to what you may read elsewhere, these pins and wires are not used or required to implement 100BASE-TX duplexing--they are just plain wasted.

Community
  • 1
JP Alioto
  • 6,450
  • 29
  • 29
4

OW O GW B BW G BrW Br

GW G OW B BW O BrW Br

In other words swap the orange/white with the green/white and the orange with the green on one end of the cable. Compare against a standard cable to make sure you have it right. Make sure you only unwravel as much of the cable ends as you need. Too much will cause crosstalk.

One time I made so many CAT5 patch cables my fingers started to bleed.

Kenneth Cochran
  • 2,299
  • 3
  • 18
  • 17
  • Obviously he'll have to make sure he has a source for the correct positioning of the colours (either a correct cable, or a document indicating where they should go), otherwise swapping some colours around might not work ;) – jerryjvl Jul 30 '09 at 02:34