Cisco Systems 3200 User Manual

The router cannot automatically negotiate port speed and duplex mode unless the connecting port is 
configured speed auto, duplex auto, or no speed. If the port speed is set to a value other than auto, such 
as 10, 100, or 1000-Mbps, configure the remote link partner port to match the local settings; do not 
configure the link partner port to auto.

If a copper Gigabit Ethernet port speed is configured as 1000-Mbps, it must be configured as duplex 
auto mode; otherwise the link will not come up. We recommend that you use the speed auto command 
and duplex auto command to configure a Gigabit Ethernet port.

The fiber-optic Gigabit Ethernet port does not allow users to configure the mode as speed or duplex. The 
port speed and mode are determined by the SFP module.

Changing the Ethernet port speed and duplex mode configuration might shut down and reenable the 
interface during the reconfiguration.

The procedure to set the port speed for a copper Gigabit Ethernet port is as follows:

To set the mode on a copper Gigabit Ethernet port to duplex?

The Gigabit Ethernet optical fiber interface only supports full duplex mode; a Cisco IOS command to 
set the mode is not is supported.

Router(config)# interface GigabitEthernet slot/port

Selects the Ethernet port to be configured.

Router(config-if)# speed {10 | 100 | 1000 | auto}

Sets the speed of the Ethernet interface.

Router(config-if)# no speed 

Reverts to the default configuration (speed 
auto). If you set the port speed to auto on a 
10/100/1000-Mbps Ethernet port, speed is 
autonegotiated.

Router(config)# interface GigabitEthernet slot/port 

Selects the Ethernet port to be configured.

Router(config-if)# duplex [auto | full | half] 

Sets the duplex mode of the Ethernet port.

Router(config-if)# no duplex 

Reverts to the default configuration (duplex 
auto).