quick question??

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afternoon,

CCNA book states that when two devices receive and transmit data on the same pins, a cross over cable is required..

so a PC connected to a router will require a cross over..

but from my experience, when ever ive set up a router connecting to a PC, i cant remember using a crossover cable... things work...

why does the book state a cross over cable is needed?

thanks

 

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Is it a home or small business router from an ISP? If so those are really router, switch, and sometime WAP combination devices so you are really plugging in to what amounts to a switch port.

Cisco also has WIC cards for routers that are like little switches. So you could be plugging in to something like this: http://www.cisco.com/en/US/products/hw/routers/ps221/products_data_sheet09186a00801c749d.html


Oh and just to confuse the cabling a bit more for the real world don't forget about the MIDX auto command for interfaces on switches which is used to enable automatic media-dependent interface with crossover detection.

 

It's because a lot of NIC's have the functions of a crossover cable built in, which is why it's not always required. A crossover cable has receiving and transmitting functionality on both ends which allows it to transmit full data between ethernet devices.

 

I didn't realize that many NICs had that capability. A quick google search shows quite a few network cards with Auto-MDIX. The simplest solution or answer is usually the best!!

 

Just remember that you are studying for the CCNA which I do not think take those into consideration.

 

That's the key to that sentence. Not all devices RX/TX on the same pins. I would imagine the majority of devices designed to have NICs plugged in to them would have the pins crossed-over internally.