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Software Configuration Guide—Release 12.2(25)SG
OL-7659-02
Chapter4 Configuring Interfaces
Configuring Optional Interface Features
You can configure the interface speed and duplex mode parameters to auto and allow the Catalyst 4500
series switch to negotiate the interface speed and duplex mode between interfaces. If you decide to
configure the interface speed and duplex commands manually, consider the following:
•If you enter the no speed command, the switch automatically configures both interface speed and
duplex to auto.
•When you set the interface speed to 1000 (Mbps) or auto 1000, the duplex mode is full duplex. You
cannot change the duplex mode.
•If the interface speed is set to 10 or 100, the duplex mode is set to half duplex by default unless you
explicitly configure it.
Caution Changing the interface speed and duplex mode configuration might shut down and restart the interface
during the reconfiguration.
Setting the Interface Speed
If you set the interface speed to auto on a 10/100-Mbps Ethernet interface, speed and duplex are
autonegotiated. The forced 10/100 autonegotiation feature allows you to limit interface speed auto
negotiation up to 100 Mbps on a 10/100/1000BASE-T port.
To set the port speed for a 10/100-Mbps Ethernet interface, perform this task:
This example shows how to set the interface speed to 100 Mbps on the Fast Ethernet interface5/4:
Switch(config)# interface fastethernet 5/4
Switch(config-if)# speed 100
This example shows how to allow Fast Ethernet interface5/4 to autonegotiate the speed and duplex
mode:
Switch(config)# interface fastethernet 5/4
Switch(config-if)# speed auto
Note This is analogous to specifying speed auto 10 100.
This example shows how to limit the interface speed to 10 and 100 Mbps on the Gigabit Ethernet
interface1/1 in auto-negotiation mode:
Switch(config)# interface gigabitethernet 1/1
Switch(config-if)# speed auto 10 100
This example shows how to limit speed negotiation to 100 Mbps on the Gigabit Ethernet interface 1/1:
Switch(config)# interface gigabitethernet 1/1
Switch(config-if)# speed auto 100
Note Turning off autonegotiation on a Gigabit Ethernet interface will result in the port being forced into
1000 Mbps and full-duplex mode.
Command Purpose
Step1 Switch(config)# interface fastethernet
slot/interface
Specifies the interface to be configured.
Step2 Switch(config-if)# speed [10 | 100 | auto [10 | 100]] Sets the interface speed of the interface.