Router to Router cabling question...

Ok so if I was connecting router to router I would use a crossover cable, but I bought some kit off ebay and simply plugged it all in without erasing the config. I used router to router with a straight through cable and it worked...

I erased the config and it stopped working. I forgot to check the running config, is there some setting that allows straight through router to router?

Tell me I'm not going crazy...

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SecurityThroughObscurity

could be auto mdi-x configuration
but I am not sure.

fredrikjj

nevermind

xnx

What 2 routers were you connecting?

wallpaper_01

A 2811 and a 2691. Had set up a link and pinged over the ports.

I had everything working, all lights on, erased the startup config and it stopped working. Then I realised of course it had because it was a straight through cable... Which is why im confused it was working in the first place!

Honestly, I could be going mad, but I swear I did not change anything round.

IF there is no possible way they could communicate thats fine but im wondering if there is some sort of way they can switch inside, that I don't know about. Better to ask than to dismiss...

wallpaper_01

SecurityThroughObscurity wrote: »

could be auto mdi-x configuration
but I am not sure.

Thanks, this sounds plausable from doing a google search.

fredrikjj wrote: »

nevermind

no!all!

SecurityThroughObscurity wrote: »

could be auto mdi-x configuration
but I am not sure.

^this sounds about right

Doyen

You are correct about MDIX. When I started to build my lab at home from parts acquired from eBay, ran into this issue as well and thought I was losing my mind. The reason being is that I would use the same “incorrect” cord to connect to another like device and it would work on one model but then not work on another of the same model.

After doing some research, I found that it was because certain devices had auto-MDIX enabled (globally) while some did not. I am assuming it was disabled on certain models that I purchased due to the security of the environment it came from unauthorized connections to another router/switch without a cross-over cable. When you have auto-MDIX enabled, you can use either type of cable to connect to other like devices and the interface will automatically correct any incorrect cabling. I’ve had issues with getting MDIX to work properly and found that if you set the duplex and speed of the interface to auto, it seems to work flawlessly.

Personally, I disabled it on all of my devices to force me to recognize cables (straight, cross-over, & roll-over) during my studies & labbing. If you wanted to use it on an interface (config-if), you would type “mdix auto”. To disable it on an interface, you would type “no mdix auto”. “show interfaces” will also display if you have mdix enabled or not.

For those that are studying for their CCENT or CCNA, here is my method of remembering cabling if you associate "devices" with “gender relationships”:

If you like to connect to different devices, then you are STRAIGHT.
If you like to connect to the same devices, then you are CROSSing Over.

devils_haircut

^^The exception to that being PC->Router, where you would also need to use a crossover cable.

davenull

Doyen wrote: »

I’ve had issues with getting MDIX to work properly and found that if you set the duplex and speed of the interface to auto, it seems to work flawlessly.

That's the trade-off of using MDIX. It's not possible to enable MDIX and still have hard-coded speed and duplex. I don't work in the industry yet but I'm getting a vibe that the best practice is to always assign speed and duplex manually hence proper cables are needed.

wallpaper_01

Thanks people, its always best to ask than to wonder. Learned something new and hope it helps someone else.

jeffgibbs

@ Doyen .... Good advice on disabling the auto MDIX feature. I had not thought about it. Love the leaning tower. It looks like a good setup. Like the people in the other thread were saying it does need to be secured .... somehow.

Doyen

So far, my "leaning tower of Cisco" setup works. I will get around to re-balancing it to make it more stable, but I never seem to get around to doing it since I use that time for labbing purposes instead. Most likely, when I purchase some devices for CCNA Security studies, I will reorganize it