[CentOS] 2 Ethernet cabling question

John R Pierce pierce at hogranch.com
Sat Dec 25 17:27:13 UTC 2010


On 12/25/10 6:42 AM, S Mathias wrote:
> Two questions that was not always clear for me [sorry for posting to this list :\]:
>
> ##############################################################################################
>
> Q1) when cabling, is the color order important? like:
>
> straight cabling:
> A side: white-orange, orange, white-green, blue, white-blue, green, white-brown, brown
> B side: white-orange, orange, white-green, blue, white-blue, green, white-brown, brown
>
> could be eg.: like this??
> A side: white-orange, brown, white-blue, green, white-green, blue, white-brown, orange
> B side: white-orange, brown, white-blue, green, white-green, blue, white-brown, orange

no.  its critical that the pairs be maintained.    ethernet uses 
differential signalling on pairs.    whote/orange and orange/white are a 
twisted pair, as is each other combination of white/color and 
color/white.   the longer the cable, the more critical this becomes (eg, 
you could perhaps get away with it on a 2 meter patch cord, but a 30 
meter run in a wall would most certainly have crosstalk problems).

> ##############################################################################################
>
> Q2) again cabling.. i know what is the color order of straight and crossover cabling. BUT: what are the color orders, when i need to create physically two separated networks?

terrible idea.    gigE uses all 4 pairs for a single connection anyways, 
so you *can't* double up on a patch cord.

> 568B; straight; nic to switch:
> A side: white-orange, orange, white-green, blue, white-blue, green, white-brown, brown
> B side: white-orange, orange, white-green, blue, white-blue, green, white-brown, brown
> ----------
> 568A; crossover; nic to nic: [it's not so important about from ~2005]:
> switch the pairs: 1&2 with 3&6 on one side:
> A side: white-green, green, white-orange, blue, white-blue, orange, white-brown, brown
> B side: white-orange, orange, white-green, blue, white-blue, green, white-brown, brown


568A and B aren't straight vs crossover. they are simply two different 
schemes for the order of the pairs to the connector. basically, they 
swap the green and orange pairs.

I would stick with T568A


> ----------
> one cable, two straight networks:
> A side:
> 	I.:
> 	II.:
> B side:
> 	I.:
> 	II.:
> ----------
> one cable, two crossover networks:
> A side:
> 	I.:
> 	II.:
> B side:
> 	I.:
> 	II.:
> ----------
> one cable, one straight and one crossover network:
> A side [straight]:
> 	I.:
> 	II.:
> B side [crossover]:
> 	I.:
> 	II.:
> ----------
> one cable, one crossover and one straight network:
> A side [crossover]:
> 	I.:
> 	II.:
> B side [straight]:
> 	I.:
> 	II.:

thats giving me a headache just thinking about it.   DO NOT PUT TWO NICs 
ON ONE RH45 CONNECTOR




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