To configure Layer 2 parameters, if the interface is in Layer 3 mode, you must enter the switchport interface configuration command without any parameters to put the interface into Layer 2 mode. This shuts down the interface and then re-enables it, which might generate messages on the device to which the interface is connected. When you put an interface that is in Layer 3 mode into Layer 2 mode, the previous configuration information related to the affected interface might be lost, and the interface is returned to its default configuration.
Automatic medium-dependent interface crossover (auto-MDIX) is enabled by default. When you enable auto-MDIX, you must also set the interface speed and duplex to auto so that the feature operates correctly.
Auto-MDIX is supported on all 10/100/1000-Mb/s and on 10/100/1000BASE-TX small form-factor pluggable (SFP)-module interfaces. It is not supported on 1000BASE-SX or -LX SFP module interfaces.
Restrictions for Auto-MDIX
The switch might not support a pre-standard powered device—such as Cisco IP phones and access points that do not fully support IEEE 802.3af—if that powered device is connected to the switch through a crossover cable. This is regardless of whether auto-MIDX is enabled on the switch port.
Information about Configuring Auto-MDIX
Auto-MDIX on an Interface
When automatic medium-dependent interface crossover (auto-MDIX) is enabled on an interface, the interface automatically detects the required cable connection type (straight through or crossover) and configures the connection appropriately. When connecting switches without the auto-MDIX feature, you must use straight-through cables to connect to devices such as servers, workstations, or routers and crossover cables to connect to other switches or repeaters. With auto-MDIX enabled, you can use either type of cable to connect to other devices, and the interface automatically corrects for any incorrect cabling. For more information about cabling requirements, see the hardware installation guide.
This table shows the link states that result from auto-MDIX settings and correct and incorrect cabling.
Table 1 Link Conditions and Auto-MDIX Settings
Local Side Auto-MDIX
Remote Side Auto-MDIX
With Correct Cabling
With Incorrect Cabling
How to Configure Auto-MDIX
Configuring Auto-MDIX on an Interface
Command or Action
Switch# configure terminal
Enters global configuration mode
Switch(config)# interface gigabitethernet1/0/1
Specifies the physical interface to be configured, and enter interface configuration mode.
Switch(config-if)# speed auto
Configures the interface to autonegotiate speed with the connected device.
Switch(config-if)# duplex auto
Configures the interface to autonegotiate duplex mode with the connected device.
Switch(config-if)# mdix auto
Enables auto-MDIX on the interface.
Returns to privileged EXEC mode.
show controllers ethernet-controllerinterface-idphy
Verifies the operational state of the auto-MDIX feature on the interface.
Example for Configuring Auto-MDIX
This example shows how to enable auto-MDIX on a port:
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