Configuring Auto-Mdix On A Port - Cisco Catalyst 3750 Software Configuration Manual

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.
ES ports do not support 10 or 100 Mbps operation. When a 1000BASE-T SFP module is inserted in an
Caution
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
Table 9-2
Local Side Auto-MDIX
On
On
Off
Off
Beginning in privileged EXEC mode, follow these steps to configure Auto-MDIX on a port:
Command
Step 1
configure terminal
Step 2 interface interface-id
Step 3
speed auto
Step 4
duplex auto
Step 5
mdix auto
Step 6 end
Step 7
show controllers ethernet-controller
interface-id phy
Step 8
copy running-config startup-config
Catalyst 3750 Metro Switch Software Configuration Guide
9-16
shows the link states that results from auto-MDIX settings and correct and incorrect cabling.
Link Conditions and Auto-MDIX Settings
Remote Side Auto-MDIX With Correct Cabling
On
Off
On
Off
Purpose
Enter global configuration mode
Enter interface configuration mode for the physical interface to be
configured.
Configure the port to autonegotiate speed with the connected device.
Configure the port to autonegotiate duplex mode with the connected device.
Enable Auto-MDIX on the port.
On an ES port, setting the speed to auto can result in severe data
Note
loss if the port is connected to a 10/100 interface on another switch.
Return to privileged EXEC mode.
Verify the operational state of the Auto-MDIX feature on the interface.
(Optional) Save your entries in the configuration file.
Chapter 9 Configuring Interface Characteristics
With Incorrect Cabling
Link up Link up
Link up Link up
Link up Link up
Link up Link down
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