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Catalyst 2950 and Catalyst 2955 Switch Command Reference
OL-10102-01
Chapter 2 Catalyst 2950 and 2955 Cisco IOS Commands
duplex
On Catalyst 2950 Long-Reach Ethernet (LRE) switches, use the duplex command to configure both the
MAC and LRE chipsets.
A 10/100/1000 LRE switch port autonegotiates with the device at the other end of the link for the duplex
setting and then forces the duplex setting to the negotiated value. A fiber-optic connection (SFP) also
autonegotiates with the device at the other end of the link but only accepts a connection at full duplex.
The duplex setting for a SFP Gigabit Ethernet port has a close relationship to the setting for speed.
Fiber-optic connections are always forced to 1000 Mbps and full-duplex mode. Copper connections can
run at either full- or half-duplex mode for 10 or 100 Mbps but are can only run in full-duplex mode at
1000 Mbps. When you manually set the speed and duplex settings, autonegotiation is disabled, and
speed and duplex settings can cause a mismatch.
Note For guidelines on setting the switch speed and duplex parameters, see the software configuration guide
for this release.
Examples This example shows how to set a port to half duplex:
Switch(config)# interface fastethernet0/1
Switch(config-if)# duplex half
This example shows how to set a port to full duplex:
Switch(config)# interface fastethernet0/1
Switch(config-if)# duplex full
You can verify your settings by entering the show interfaces transceiver properties or
show running-config privileged EXEC command.
Related Commands Command Description
cpe duplex Sets the duplex setting for customer premises equipment (CPE) Ethernet
ports.
local duplex Sets the duplex mode on an LRE port.
show running-config Displays the configuration information running on the switch. For syntax
information, select Cisco IOS Configuration Fundamentals Command
Reference for Release 12.1 > Cisco IOS File Management Commands >
Configuration File Commands.
speed Sets the port speed.
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