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Catalyst 3750 Switch Software Configuration Guide
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Chapter 11 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, refer to the hardware installation guide.
Auto-MDIX is enabled by default. When you enable Auto-MDIX, you must also set the speed and duplex
on the interface to auto in order for the feature to operate correctly. Auto-MDIX is supported on all
10/100 and 10/100/1000 Mbps interfaces and on 10/100/1000 BASE-T/TX SFP interfaces. It is not
supported on 1000 BASE-SX or -LX SFP interfaces.
Table 11-2 shows the link states that results from Auto-MDIX settings and correct and incorrect cabling.
Beginning in privileged EXEC mode, follow these steps 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
Switch(config-if)# mdix auto
Switch(config-if)# end
Table 11-2 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
Step 1
configure terminal Enter global configuration mode
Step 2
interface interface-id Enter interface configuration mode for the physical interface to be
configured.
Step 3
speed auto Configure the interface to autonegotiate speed with the connected device.
Step 4
duplex auto Configure the interface to autonegotiate duplex mode with the connected
device.
Step 5
mdix auto Enable Auto-MDIX on the interface.
Step 6
end Return to privileged EXEC mode.
Step 7
show controllers ethernet-controller
interface-id phy
Verify the operational state of the Auto-MDIX feature on the interface.
Step 8
copy running-config startup-config (Optional) Save your entries in the configuration file.
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