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Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter12 Configuring Interface Characteristics
Configuring Ethernet Interfaces
Switch models can include combinations of Fast Ethernet (10/100-Mb/s) ports, Gigabit Ethernet
(10/100/1000-Mb/s) ports, 10-Gigabit module ports, and small form-factor pluggable (SFP) module
slots supporting SFP modules.
These sections describe how to configure the interface speed and duplex mode:
Speed and Duplex Configuration Guidelines, page12-18
Setting the Interface Speed and Duplex Parameters, page12-19
Speed and Duplex Configuration Guidelines
When configuring an interface speed and duplex mode, note these guidelines:
Fast Ethernet (10/100-Mb/s) ports support all speed and duplex options.
Gigabit Ethernet (10/100/1000-Mb/s) ports support all speed options and all duplex options (auto,
half, and full). However, Gigabit Ethernet ports operating at 1000 Mb/s do not support half-duplex
mode.
You cannot configure the speed or duplex mode on 10-Gigabit module ports; these ports operate
only at 10,000 Mb/s and in full-duplex mode.
For SFP module ports, the speed and duplex CLI options change depending on the SFP module type:
The 1000BASE-x (where -x is -BX, -CWDM, -LX, -SX, and -ZX) SFP module ports support
the nonegotiate keyword in the speed interface configuration command. Duplex options are not
supported.
The 1000BASE-T SFP module ports support the same speed and duplex options as the
10/100/1000-Mb/s ports.
The 100BASE-x (where -x is -BX, -CWDM, -LX, -SX, and -ZX) SFP module ports support only
100 Mb/s. These modules support full- and half- duplex options but do not support
autonegotiation.
For information about which SFP modules are supported on your switch, see the product
release notes.
If both ends of the line support autonegotiation, we highly recommend the default setting of auto
negotiation.
If one interface supports autonegotiation and the other end does not, configure duplex and speed on
both interfaces; do not use the auto setting on the supported side.
When STP is enabled and a port is reconfigured, the switch can take up to 30 seconds to check for
loops. The port LED is amber while STP reconfigures.
Caution Changing the interface speed and duplex mode configuration might shut down and re-enable the
interface during the reconfiguration.