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TOPIC: Switch question

Switch question 6 years 8 months ago #33486

  • Nevins
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According to my reading on UTP cabling Straight-Though cable is used when connecting devices that transmit on pins 1, 2 and receive on 3,6 only when connecting to devices that receive on 3,6 and transmit on 1,2. Cross over cables are only used with transmit and receive pairs are the same.

Why is it that the switches I've seen use Straight-Though cables when connecting to other switches? Shouldn't it use a cross over cable or does it not matter because newer switches can figure out the line cross?
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Re: Switch question 6 years 8 months ago #33489

  • FlipRich
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Hmm.. Not so sure about that. I've always connected my switches, and anything else Layer 2, together with a crossover.
Rich
Network Engineer /CCNP, CCNA-S
Tallahassee, FL
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Re: Switch question 6 years 8 months ago #33495

  • Nevins
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Well the book I'm looking at specifically says:


These devices transmit on 1,2 and receive on 3,6:

PC NICs
Routers
Wireless Access Points (Ethernet interface)
Networked printers (printers that connect directly to the lan)


Devices that transmit on 3,6 and receiver on 1,2:
Hubs
Switches


With the basic rule that if you transmit on one end you have to receive on the other otherwise your sending data into data. Meaning that you can use a straight though on and device that is in group one connecting to group 2 but any same group devices need to have the cross-over.




An example would be a hub connected to another hub



If it sends on pins 3, 6 on both sides it's transmitting into it's transmitters which clearly shouldn't work.




However in the case of some switches Straight-Though clearly works just fine. I don't understand how this is possible.

(I guess the problem I'm having is the book says one thing but the real switches that I've used in the past physically tell a different story)



This diagram I made shows how based on what I've read things should work but in the real world the switches I've dealt with still somehow work. I may be answering my own question but how does a switch function when a rX is connected to an rX when it should be crossed over?
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Re: Switch question 6 years 7 months ago #33500

  • Perlhack
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I've use straight and cross over on switch to switch connections as well. Auto-MIDX can make corrections if a straight connection is used.

en.wikipedia.org/wiki/Auto-MDIX
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Re: Switch question 6 years 7 months ago #33502

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Makes sense. Thank you.
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