Cisco Auto MDI/MDIX Switch Support Matrix

You don’t need to use a crossover cable anymore to connect a switch to another one. Actually, the correct name of this switch feature is Auto MDIX (Medium dependent interface crossover). Let’s make a long story short. You just need a straight-through cable in between the PC (MDI type) and switch (MDIX type). A crossover cable is necessary when you have the same type on both ends like PC-to-PC or switch-to-switch connection. If the device supports Auto MDIX, it changes its port type itself according to the other side.

You MUST enable speed and duplex auto negotiation as prerequisite. You have to write down below commands on a Cisco switch to enable it.

speed auto
duplex auto
mdix auto

However Auto MDIX does not supported by all Cisco Catalyst switches.

Cisco Switches without Auto MDIX support
Catalyst 2950
Catalyst 3550
Catalyst 4948

Cisco Switches with Auto MDIX support
Catalyst 2940
Catalyst 2960
Catalyst 2970
Catalyst 3560
Catalyst 3750
Cisco IE 3000

FAQ Section:
Q1) Which pins are in use in MDI &MDIX type ports?
MDI : Pins:1 , 2 transmit 3 , 6 receive
MDIX : Pins:1 , 2 receive 3 , 6 transmit

Q2) Does it work if I use a crossover cable with an Auto MDIX port?
Yes, it does. Both straight-through and crossover cables work fine.

Q3) Can I fix speed & duplex and use Auto MDIX?
No. Auto MDIX uses speed negotiation process to recognize the other side’s port type. You have to use a crossover cable if you want to fix speed and duplex.

Q4) Do I need Auto MDIX on both interfaces to let it works?
No. It is enough if just one interface supports Auto MDIX but speed and duplex should be auto on both interfaces.

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