Understanding the Features of Auto-MDIX

[Translator]

Hello, my client company replaced the equipment and connected the cable, but I received a message that the link did not live.

Only the trunk setting is set.


C1000FE-24T-4G-L
interface gi 1/0/1
switchport mode trunk

C1000FE-48T-4G-L
interface gi 1/0/1
switchport mode trunk


While I was looking for documents, I found out about the functions of Auto-MDIX
Someone says the link might not live if Auto-MDIX check cycles are the same on both sides with a very rare probability.
Can anyone explain this to me?

Both switches are version 15.2(7)E7 or later.

[marce1000]

 - I doubt if auto-mdix is involved because these days all of that is automated and every device 'has it'
   Check logs on the devices when the trunk link connection is attempted , also look at the status of the interfaces
   and the port counters (for instance)

 M.

[Giuseppe Larosa]

Hello ,

the Auto MDIX allow the two ports to detect the need for one of them to "cross connect"  in order to build a connection using a straight LAN cable.

Before MDIX introduction we needed to use crossover LAN cables to interconnect switch to switch or router to router or PC to PC.

To be noted a switch port is different from a PC or router port and it is ready to  serve a PC or router port using a straight cable.

One possible option is to have the customer to try to use a crossover cable.

In some specific cases this is still needed usually for some multi vendor connections

Hope to help

Giuseppe

[Joseph W. Doherty]

"Someone says the link might not live if Auto-MDIX check cycles are the same on both sides with a very rare probability."

Unaware of such, so if someone could provide a reference, that would be nice.

Not all devices support auto-MDI.  I don't know if those devices do.  On Cisco devices that do, auto negotiation normally needs to be enabled.

@Giuseppe Larosa makes a good suggestion, try a cross over cable.  If not already tried, try a different straight thru cable too.

[Leo Laohoo]

Default the config of Gi 1/0/1.  

Connect Gi 1/0/1 to, say, Gi 1/0/12.  Does the ports go "up"?