[rescue] Rescued Sun servers, now what?!
mouse at Rodents-Montreal.ORG
Mon Feb 20 09:44:35 CST 2012
>> You didn't need to use crossover cable everywhere (i.e. on Gigabit
>> NIC), but on 100Mbit/s you should. And it's Cat-5(e) cable.
Well, some 100Mb interfaces - especially on switches - are also auto-X
and thus you don't need to worry about crossover vs straight.
> [picks up an Ethernet cable and looks at it]
> "YFC UTP PATCH ISO/IEC 11801 & FN 50280 & TIA/EIA 568B.2 3P VERIFIED
> FOR GIGABIT ETHERNET 24AWGx4P TYPE CM (UL) C(UL) CMH E164469-E3"
That's describing the wire itself. The difference between crossover
and straight-through lies not in the wire but rather in how it's
Hold one of the ends so the shiny metal contact surfaces face you (the
locking tab will be behind the rest of the connector). Now look just
adjacent to those contacts, in the direction towards the cable. You
should see a wire colour for each contact (half of them will probably
Now compare that with the other end. If the colour pattern is the
same, it's a straight-through cable; if two of them have been switched,
it's a crossover cable. (That's assuming it's a twisted-pair-Ethernet
cable at all, of course; while it's overwhelmingly likely it is,
especially in view of the markings you quote, there are a few other
things RJ45-style 8P8C connectors are used for.)
If you hold the cable end with the wire pointing down towards your
feet, the contact surfaces towards you, and number the pins from 1 to 8
left to right, then a crossover cable swaps pins 1 and 3 and also swaps
pins 2 and 6 (as compared to the other end of the cable). One of those
pairs will probably both be white wires and thus the swap of those
wires will be invisible, but the other pair will normally be orange and
green or some such and thus the swap will be visible.
If you have an ohmmeter, you can verify that way (you may need small
bits of wire to make contact with the connector surfaces). A
straight-through cable connects pin 1 on one end to pin 1 on the other
end, 2 to 2, etc, all the way up to 8 to 8; a crossover cable connects
1 to 3, 2 to 6, 3 to 1, 4 to 4, 5 to 5, 6 to 2, 7 to 7, and 8 to 8.
(The peculiar-looking choice of wires to swap is of historical origin;
I can elaborate if you're curious, but this mail is already long
enough.) 10Mb or 100Mb cables may not hav wires to pins 4, 5, 7, and
8, but a gigabit cable will have all eight, and most 10- or 100-Mbit
cables also have all eight in my experience. (The wire is marked as
gigabit-ready, yes, but that does not necessarily mean the cable was
prepared for gigabit use, though it probably is.)
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