Mixing straight Cat5e and Cat6 cables results in a crossover connection


Yesterday I finished running about 40 meters of FTP Cat6 cable through the electrical conduit, from the first floor to the attic. Both ends of the cable are terminated as T568B on Cat6 wall jacks. So, I now have a Cat6 ethernet jack in my living room and another Cat6 jack in my studio in the attic.

To test that everything was OK, I connected a cat5e cable from the living room jack to the main router, and then up in the attic I connected another cat5e cable from the ethernet jack to a laptop. And absolutely nothing happened, the laptop didn't even recognize a cable was connected. A bit puzzled, I then used a network cable tester to see if the cable was indeed OK, and, to my astonishment, the tester said it was a crossover cable.

I double checked the termination on both ends and they are indeed T568B. The rest of my network and all my cables are T568B as well. It then occurred to me that maybe using Cat5e cables to complete the connection from my router to the laptop was the problem, as I am effectively mixing Cat5e and Cat6 cables in a single connection, if you know what I mean. Could that be the problem? I won't be able to test the connection with Cat6 cables until later this afternoon, but wanted to know whether mixing Cat5e and Cat6 cables in the manner I've done can cause the connection to be labelled as crossover when, in fact, it should be straight.

Best Answer

No. On of the pieces of the connection (either Cat5 cable or the Cat6 cable) is a cross over. In addition make sure you're not using an uplink port on your router as that might be crossed. Up to date routers and switches usually should be able to use MDI-X to automatically switch whenever it should be a crossover port or not.

Test both Cat5 cables whenever they're straight or not. If both are straight chances are that the Cat6 is a crossover, maybe because someone wasn't paying attention while assembling the termination points.

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