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PostPosted: Sat Nov 06, 2010 3:44 am 
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So I am trying to brush up on some old ****, and maybe learn some new stuff...

One area where I never bothered to learn was making cable. I get the basic gist of it.

eis/tia 568a
Pin Color
1 white/green
2 green
3 white/orange
4 blue
5 white/blue
6 orange
7 white/brown
8 brown

eis/tia 568b
Pin Color
1 white/orange
2 orange
3 white/green
4 blue
5 white/blue
6 green
7 white/brown
8 brown

I also know that to make a T1 Loopback adapter you:
pin 1 loop to pin 4
pin 2 loop to pin 5

Now here is what I am trying to figure out... crossover cabling. This has made me want to pound a 10 penny nail into my monitor and release the magic smoke...

if you look at THIS link it says:
w/o to w/g
o to g
wg to wo
bl to bl
wbl to wbl
g to o
wbr to wbr
br to br

But if you look at THIS link... it says:
wo to wg
o to g
wg to wo
bl to wbr
g to o
wbr to bl
br to wbl

And someone tried to give me a pop quiz on how to just label a crossover cable pin to pin (as I did with the loopback adapter) but I have no frikking clue.

and how the hell do I figure out PoE??

Is remembering how to wire a crossover cable even needed anymore? I thought newer hardware rendered that almost obsolete.

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PostPosted: Sat Nov 06, 2010 8:57 am 
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Different standards -

http://en.wikipedia.org/wiki/TIA/EIA-568
http://en.wikipedia.org/wiki/Ethernet_crossover_cable

Quote:
The primary thing one has to be careful of is not to accidentally wire the ends of the same cable according to different configurations (unless one intends to create an Ethernet crossover cable).


http://www.ablecables.com.au/568avb.htm#_Toc426467840
Quote:
8.0 Which Specification is Preferred?

If 568A and 568B specifications are technically identical and both are international standards which one is preferred? The information here is sketchy and I have not received a response from many standards organizations, from what I can understand is that although 568B is widespread (especially in the USA) all new installations should be carried out using the TIA/EIA developed 568A. Standards Australia – The Australian equivalent the ISO says, "There is no reason to change existing 568B installations to 568A although all new installations should be implemented with 568A." More recent information, "As published in the EIA Commercial Building Draft 9.0 as the preferred sequence for termination of UTP data cabling… This is also the preferred option for AS/NZS 3080."


Bottom line, it doesn't make a lot of difference in actual practice if you're only using pins 1,2,3 and 6. GigE uses all the pairs, but I don't know where I'd ever use a GigE in a crossover configuration... everything I've done in the last 10 years connect switches via fiber, not copper, and home stuff auto-connects.
Quote:
Although this crossover is called out in the Gigabit Ethernet standard[1], all Gigabit PHYs feature an auto-MDIX capability and are designed for compatibility with the existing 100BASE-TX crossovers. The IEEE specified Gigabit crossover is generally seen as unnecessary.


I use this:
http://bnoack.com/index.html?http&&&bno ... /CAT5.html

straight
Image

crossover
Image

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PostPosted: Sun Nov 07, 2010 9:32 pm 
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Taskiss wrote:
GigE uses all the pairs, but I don't know where I'd ever use a GigE in a crossover configuration... everything I've done in the last 10 years connect switches via fiber, not copper, and home stuff auto-connects.

I have a little two-node cluster at work for basic fault-tolerance. The have three 1Gb NICs -- one for the LAN, one for the SAN, and one is a crossover between the nodes. They do DRBD, cluster traffic/heartbeats, and Xen migrations over the crossover cable. You won't see that in big iron environments because at that level, no one does two-node clusters (arguably not a "real" cluster, since there's no quorum). It's a fairly common setup for simple small-to-medium business clusters like this, though.

Edit: Hah, wow -- I just noticed that quote. I didn't realize that *all* standards-compliant Gb Ethernet devices were guaranteed to auto-cross. Welp, The More You Know(TM)...

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PostPosted: Sun Nov 07, 2010 9:42 pm 
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The thing to remember when doing crossovers is that you swap green and orange, as well as blue and brown.

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PostPosted: Fri Nov 12, 2010 4:55 pm 
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Grrr... Eat your oatmeal!!
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thank you guys

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