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Catalyst 3750 Switch Command Reference
OL-8552-07
Chapter 2 Catalyst 3750 Switch Cisco IOS Commands
duplex
duplex
Use the duplex interface configuration command to specify the duplex mode of operation for a port. Use
the no form of this command to return the port to its default value.
duplex {auto | full | half}
no duplex
Syntax Description
Defaults The default is auto for Fast Ethernet and Gigabit Ethernet ports.
The default is full for 100BASE-x (where -x is -BX, -FX, -FX-FE, or - LX) SFP modules.
Duplex options are not supported on the 1000BASE-x (where -x is -BX, -CWDM, -LX, -SX, or -ZX)
SFP modules.
For information about which SFP modules are supported on your switch, see the product release notes.
Command Modes Interface configuration
Command History
Usage Guidelines This command is not available on a 10-Gigabit Ethernet interface.
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.
Note Half-duplex mode is supported on Gigabit Ethernet interfaces if the duplex mode is auto and the
connected device is operating at half duplex. However, you cannot configure these interfaces to
operate in half-duplex mode.
auto Enable automatic duplex configuration; port automatically detects whether it
should run in full- or half-duplex mode, depending on the attached device mode.
full Enable full-duplex mode.
half Enable half-duplex mode (only for interfaces operating at 10 or 100 Mb/s). You
cannot configure half-duplex mode for interfaces operating at 1000 or
10,000
Mb/s.
Release Modification
12.1(11)AX This command was introduced.
12.1(20)SE Support for the half keyword was added for the 100BASE-FX SFP module.
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