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MDI or MDIX ?

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'chris'
Super Advisor

MDI or MDIX ?

hi

I have a ADSL router connected via straight-through patch cable to the switch.
Both Ethernet devices (router & switch) are hard coded to 100FD.
At the switch I cannot use AUTO for MDI/MDIX.
Should I enable MDI or MDIX in my case ?

kind regards
chris
6 REPLIES
Ron Kinner
Honored Contributor

Re: MDI or MDIX ?


I assume you are using a straight cable and that normally you would plug a PC into the router, in which case you would want to use MDIX. That should give you a link light. If you don't get a link light then try MDI or a new cable.

Ron
Les Ligetfalvy
Esteemed Contributor

Re: MDI or MDIX ?

Both the switch port and the router port would be the same. Since most devices these days are Auto-MDIX, unless you disable it on both sides it really matters not what you set the switch to since the other side would flip. If the other side does not, then simply use the one that works. Unlike duplex settings, MDI/MDIX settings are all or none.


I really REALLY R E A L L Y dislike Auto-MDIX and disable it every chance I get. At the switch console CLI, in config mode, I issue the command:
interface ethernet all mdix-mode mdix

I do not want MDIX devices connected by users or other IT coworkers to get a link without changing switch port settings. Call me a control freak if you want, but I have chased down all sorts of network problems to crappy unmanaged mini-hubs hidden behind file cabinets that someone used to add ports in an area without my knowledge.

It really irks me that these days almost every bit of cheap network junk is Auto-MDIX, making it harder for me to impede their connection to my cable plant.
'chris'
Super Advisor

Re: MDI or MDIX ?

thanks !

but do I understand correctly ?

cross-over cable MDIX
straight-through cable MDI
Les Ligetfalvy
Esteemed Contributor
Solution

Re: MDI or MDIX ?

Once again, it depends on what is on the other side. Use a straight-through jumper to connect MDI to MDIX.

It is always better to use a straight-through jumper if the port can be configured.
'chris'
Super Advisor

Re: MDI or MDIX ?

thanks, now is clear.
Gerhard Roets
Esteemed Contributor

Re: MDI or MDIX ?

Hi Cris

MDI = Strait internal wiring
MDIX = Crossed over internal wiring

Some modern devices does it electronically now. From the above you can make the following deductions to get communications going.

MDI to MDI needs crossover
MDIX to MDIX need crossover
MDI to MDIX needs strait

Most end user equipment is MDI.

I hope this clears it up.

Regards
Gerhard