Cisco Catalyst 3750 - Configuring Auto-MDIX on a Port

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Catalyst 3750 Metro Switch Software Configuration Guide
78-15870-01
Chapter 9 Configuring Interface Characteristics
Configuring Ethernet Interfaces
Configuring Auto-MDIX on a Port
When automatic medium-dependent-interface crossover (Auto-MDIX) is enabled on an port, the port
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 disabled by default. When you enable Auto-MDIX, you must also set the speed and
duplex on the port to auto in order for the feature to operate correctly. Auto-MDIX is supported on all
10/100 Mbps ports and on 10/100/1000 BASE-T/TX SFP module ports. It is not supported on
1000 BASE-SX or -LX SFP module ports.
Caution ES ports do not support 10 or 100 Mbps operation. When a 1000BASE-T SFP module is inserted in an
ES module port, if you set the speed to auto to enable Auto-MDIX, be sure that the interface is connected
to a Gigabit interface. Setting the speed to auto can result in severe data loss if the interface is connected
to a 10/100 interface on another switch.
Table 9-2 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 a port:
Table 9-2 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 port to autonegotiate speed with the connected device.
Step 4
duplex auto Configure the port to autonegotiate duplex mode with the connected device.
Step 5
mdix auto Enable Auto-MDIX on the port.
Note On an ES port, setting the speed to auto can result in severe data
loss if the port is connected to a 10/100 interface on another switch.
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.