Configuring Auto-MDIX

Prerequisites for Auto-MDIX

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.

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

On

On

Link up

Link up

On

Off

Link up

Link up

Off

On

Link up

Link up

Off

Off

Link up

Link down

How to Configure Auto-MDIX

Configuring Auto-MDIX on an Interface

Procedure

  Command or Action Purpose
Step 1

enable

Example:


Switch> enable

Enables privileged EXEC mode. Enter your password if prompted.

Step 2

configure terminal

Example:


Switch# configure terminal

Enters global configuration mode

Step 3

interface interface-id

Example:


Switch(config)# interface gigabitethernet1/0/1

Specifies the physical interface to be configured, and enter interface configuration mode.

Step 4

speed auto

Example:


Switch(config-if)# speed auto

Configures the interface to autonegotiate speed with the connected device.

Step 5

duplex auto

Example:


Switch(config-if)# duplex auto

Configures the interface to autonegotiate duplex mode with the connected device.

Step 6

end

Example:


Switch(config-if)# end

Returns to privileged EXEC mode.

Step 7

show controllers ethernet-controller interface-idphy

Verifies the operational state of the auto-MDIX feature on the interface.

Step 8

copy running-config startup-config

Example:


Switch# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

Example for Configuring Auto-MDIX

This example shows how to enable auto-MDIX on a port:


		Switch# configure terminal
		Switch(config)# interface gigabitethernet1/0/1
		Switch(config-if)# speed auto
		Switch(config-if)# duplex auto
		Switch(config-if)# mdix auto
		Switch(config-if)# end

Additional References

Error Message Decoder

Description Link

To help you research and resolve system error messages in this release, use the Error Message Decoder tool.

https://www.cisco.com/cgi-bin/Support/Errordecoder/index.cgi

MIBs

MIB MIBs Link

All supported MIBs for this release.

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs

Technical Assistance

Description Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/support