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Chapter 9
Configuring Interface Characteristics
Speed and Duplex Configuration Guidelines
When configuring an interface speed and duplex mode, note these guidelines:
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Caution
Changing the interface speed and duplex mode configuration might shut down and re-enable the
interface during the reconfiguration.
Setting the Interface Speed and Duplex Parameters
Beginning in privileged EXEC mode, follow these steps to set the speed and duplex mode for a physical
interface:
Command
Step 1
configure terminal
Step 2
interface interface-id
Step 3
no shutdown
78-17058-01
You can configure interface speed on Fast Ethernet (10/100-Mbps) and Gigabit Ethernet
(10/100/1000-Mbps) ports. You can configure Fast Ethernet ports to full-duplex, half-duplex, or to
autonegotiate mode. You can configure Gigabit Ethernet ports to full-duplex mode or to
autonegotiate. You also can configure Gigabit Ethernet ports to half-duplex mode if the speed is 10
or 100 Mbps. Half-duplex mode is not supported on Gigabit Ethernet ports operating at 1000 Mbps.
With the exception of when 1000BASE-T SFP modules are installed in the SFP module slots, you
cannot configure speed on SFP module ports, but you can configure speed to not negotiate
(nonegotiate) if connected to a device that does not support autonegotiation.
However, when a 1000BASE-T SFP module is in the SFP module slot, you can configure speed as
10, 100, or 1000 Mbps, or auto, but not as nonegotiate.
On a 100BASE-FX SFP module, you cannot configure the speed as nonegotiate.
You cannot configure duplex mode on SFP module ports; they operate in full-duplex mode except
in these situations:
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When a Cisco1000BASE-T SFP module is in the SFP module slot, you can configure duplex
mode to auto or full. Half-duplex mode is supported with the auto setting.
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When a Cisco100BASE-FX SFP module is in the SFP module slot, you can configure duplex
mode to half or full. Although the auto keyword is available, it puts the interface in half-duplex
mode (the default for this SFP module) because the 100BASE-FX SFP module does not support
autonegotiation.
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. On the Cisco ME switch, STP is supported
only on NNIs.
Purpose
Enter global configuration mode.
Specify the physical interface to be configured, and enter interface
configuration mode.
Enable the port, if necessary. By default, UNIs are disabled, and NNIs
are enabled.
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
Configuring Ethernet Interfaces
9-15
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