Auto-MDIX and the Catalyst 2955

Unanswered Question
Mar 18th, 2008

Hi --

I'm setting up an industrial network using the 2955-T switches, with two Gigabit ports and 12 fast ports. I tried connecting them with various combinations of straight-thru and crossover cables, using both the gigabit and fast ports.

My experimentation suggests that these switches have auto-MDIX enabled on the 12 fast ports, but not on the 2 gigabit ports. I have to use a crossover to connect the two with the gigabit ports. However, if I connect a gigabit port on one to a fast port on the other, either type of cable works.

The config commands don't recognize anything related to auto-mdix, either for enabling/disabling it or showing the status of the ports. I can't find anything in the docs that says that the 2955 supports auto-MDIX, although I have seen indications that the feature is being implemented on most all Cisco switches. It sure acts like it's implemented on my switches, though, at least on the fast ports.

Can anyone explain this or point me to some definitive docs? Thanks.

I have this problem too.
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owillins Mon, 03/24/2008 - 14:38

Automatic medium-dependent interface crossover (Auto-MDIX) is a feature that allows the switch interface to detect the required cable connection type (straight-through or crossover) and automatically configure the connection appropriately. With Auto-MDIX enabled, you can use either a straight-through or crossover type cable to connect to the other device, and the interface automatically corrects for any incorrect cabling.

davidrfox Tue, 03/25/2008 - 07:34

Thanks, but I know what auto-MDIX is.

My question is whether this feature is on the 2955 switch. The 2955 docs that I've found say nothing about auto-MDIX, and I don't have options for enabling or disabling it from the command line.

But the switch seems to be auto-MDIX'ing on the 12 fast ethernet ports, but not on the two gigabit ports. Is this the way it's supposed to work?

glen.grant Tue, 03/25/2008 - 08:21

I don't believe auto mdix started until the 2960 series switches.


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