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Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter12 Configuring Interface Characteristics
Configuring Ethernet Interfaces
Configuring 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.
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 and 10/100/1000-Mb/s interfaces. It is also supported on
10/100/1000BASE-TX small form-factor pluggable (SFP)-module interfaces. It is not supported on
1000BASE-SX or -LX SFP module interfaces.
Table12-3 shows the link states that result from auto-MDIX settings and correct and incorrect cabling.
Beginning in pr ivileged EXEC mod e, follow these st eps to configure auto-MDIX on an interface:
To disable auto-MDIX, use the no mdix auto interface configuration command.
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
Table12-3 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
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 interface interface-id Specify the physical interface to be configured, and enter interface
configuration mode.
Step3 speed auto Configure the interface to autonegotiate speed with the connected device.
Step4 duplex auto Configure the interface to autonegotiate duplex mode with the connected
device.
Step5 mdix auto Enable auto-MDIX on the interface.
Step6 end Return to privileged EXEC mode.
Step7 show controllers ethernet-controller
interface-id phy
Verify the operational state of the auto-MDIX feature on the interface.
Step8 copy running-config startup-config (Optional) Save your entries in the configuration file.