Duplex - Cisco Catalyst 3550 Command Reference Manual

Chapter 2 Cisco IOS Commands

duplex

Use the duplex interface configuration command to specify the duplex mode of operation for Fast
Ethernet and Gigabit Ethernet ports. Use the no form of this command to return the port to its default
value.
This command is not available on Gigabit Interface Converter (GBIC) ports. The default duplex on GBIC
Note
ports is autonegotiation.
Syntax Description
auto
full
half
Defaults
The default is auto.
Command Modes Interface configuration
Command History Release
12.1(4)EA1
Usage Guidelines
Certain ports can be configured to be either full duplex or half duplex. Applicability of this command
depends on the device to which the switch is attached.
For Fast Ethernet ports, setting the port to auto has the same effect as specifying half if the attached
device does not autonegotiate the duplex parameter.
For Gigabit Ethernet ports, setting the port to auto has the same effect as specifying full if the attached
device does not autonegotiate the duplex parameter.
You cannot configure duplex mode on GBIC interfaces.
If both ends of the line support autonegotiation, we highly recommend using the default autonegotiation
settings. If one interface supports autonegotiation and the other end does not, configure duplex and speed
on both interfaces; do use the auto setting on the supported side.
If the speed is set to auto, the switch negotiates with the device at the other end of the link for the speed
setting and then forces the speed setting to the negotiated value. The duplex setting remains as
configured on each end of the link, which could result in a duplex setting mismatch.
If both the speed and duplex are set to specific values, autonegotiation is disabled.
78-11195-09
duplex {auto | full | half}
no duplex
Port automatically detects whether it should run in full- or half-duplex mode.
Port is in full-duplex mode.
Port is in half-duplex mode.
Modification
This command was first introduced.
Catalyst 3550 Multilayer Switch Command Reference
duplex
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