Auto MDIX

[pliew]

Dear all,

I was trying to connect a Cat2950 to a Cat3750 via their gigaports. The 3750 was set with auto MDIX.

I was using straight cat-6 cables. The connection is not up. Any idea?

Thanks a lot.

Peter

[pflunkert]

Hi Peter,

here a statement from Cisco:

" You can use the mdix auto interface configuration command in the CLI to enable the automatic medium-dependent interface crossover (Auto-MDIX) feature. When the Auto-MDIX feature is enabled, the switch detects the required cable type for copper Ethernet connections and configures the interfaces accordingly. Therefore, you can use either a crossover or a straight-through cable for connections to a copper 10/100, 10/100/1000, or 1000BASE-T SFP module port on the switch, regardless of the type of device on the other end of the connection.

The Auto-MDIX feature is enabled by default on switches running Cisco IOS Release 12.2(18)SE or later. For releases between Cisco IOS Release 12.1(14)EA1 and 12.2(18)SE, the Auto-MDIX feature is disabled by default. For configuration information for this feature, refer to the switch software configuration guide or the switch command reference."

URL: http://www.cisco.com/en/US/partner/products/hw/switches/ps5023/products_installation_guide_chapter09186a00801f2707.html

You checked the cable??

Which software you use?

How is the interface configuration on both sites. When you want we can make a test in our lab.

Regards

Peter

[alagrawa]

Hi Peter,

The cat2950 doesnt support auto-mdix.

http://www.cisco.com/en/US/partner/products/hw/switches/ps628/prod_bulletin09186a00801ce930.html#wp42270

Hence you need to use cross-over cable for the link to come up.

Hope that helps.

regards

-Alok

[pflunkert]

Hi,

but the cat 3750 support this feature. This should be enough. Perhaps i should made a test in our lab ;-))

Regards

Peter.

[pliew]

Hi Peter and Alok,

Thanks so much for your feedback.

Well, apparently the problem is with the settings

on the 3700 switch. One of my engineers set the

port to have "duplex full". This setting however

will work with a cross cable between the 3700 and the 2950. But with a straight cable, it only works

with the 3700 set to "duplex auto". Stange.

Thanks a lot for your help.

Rgds

Peter

[alagrawa]

Hi,

Peter, you are probably correct. I was under the impression that both switches have to support auto-mdix to use straight-through cable.

Regarding link not coming up with with duplex full, I found the following bug: CSCee89665

http://www.cisco.com/cgi-bin/Support/Bugtool/onebug.pl?bugid=CSCee89665

Symptom:

When a switch interface is configured for speed auto and duplex full or duplex half, auto-mdix does not work.

Workaround:

Configured duplex auto instead to enable auto-mdix.

Hence, when the the duplex was configured as duplex full, auto-mdix stopped working, and so the link would not come up with a straight-through cable.

This is a known hardware limitation on the cat3750.

regards

-Alok