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
medium-dependent interface crossover (auto-MDIX) is enabled by default.
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
Auto-MDIX on an Interface
Command or Action
privileged EXEC mode. Enter your password if prompted.
Switch# configure terminal
Switch(config)# interface gigabitethernet1/0/1
physical interface to be configured, and enter interface configuration mode.
Switch(config-if)# speed auto
interface to autonegotiate speed with the connected device.
Switch(config-if)# duplex auto
interface to autonegotiate duplex mode with the connected device.
privileged EXEC mode.
Switch# copy running-config startup-config
(Optional) Saves your entries
in the configuration file.
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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