MDIX Configuration
Before Modern Networking, specific cable types (straigh-through / crossover in particular) were required to connect intermediary devices together (Switch-Switch) (Router-Router)
Nowadays we use what we know as (auto-MDIX). This is a feature on an interface that eliminates the need for a specific cable. The interface will automatically detect the required cable connection type and configures the connection as needed. In other words, you can use a normal straight-through cable to connect intermediary devices together.
With auto-MDIX enabled, any ethernet cable can be used, and the interface will automatically adjust to communicate successfully.
When using auto-MDIX on an interface, the interface speed and duplex must be set to auto so that the feature operates correctly.
Configuring Auto-MDIX
Command to enable Auto-MDIX
S1(config-if)# mdix auto
[NOTE] Usually Auto-MDIX is enable by default on modern devices.
Enter interface configuration mode
S1(config)# interface [interface-id]
Configure the interface Duplex
S1(config-if)# duplex [mode]
Configure the interface Speed
S1(config-if)# speed [speed]
Switchport Duplex and Speed Configuration Example
s1> enable S1# configure terminal S1(config)# interface fa0/1 S1(config-if)# duplex auto S1(config-if)# speed 1000 S1(config-if)# exit S1(config)#
[NOTE] Full-Duplex is always used when devices are operating at 1000Mbps/1Gpbs and/or Fiber-Optic 1000BASE-SX