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9-11
Catalyst 2950 Desktop Switch Software Configuration Guide
78-11380-05
Chapter 9 Configuring Interface Characteristics
Configuring Layer 2 Interfaces
These sections describe how to configure the interface speed and duplex mode:
• Configuration Guidelines, page 9-11
• Setting the Interface Speed and Duplex Parameters, page 9-11
Configuration Guidelines
When configuring an interface speed and duplex mode, note these guidelines:
• Ethernet ports set to 1000 Mbps should always be set to full duplex.
• Gigabit Ethernet ports that do not match the settings of an attached device can lose connectivity and
do not generate statistics.
• If both ends of the line support autonegotiation, we highly recommend the default setting of
autonegotiation.
• When connecting an interface to a 100BASE-T device that does not autonegotiate, set the duplex
mode to full or half to match the device, and set the speed to auto. Autonegotiation for the speed
setting selects the correct speed even if the attached device does not autonegotiate, but duplex mode
must be explicitly set.
• When connecting an interface to a Gigabit Ethernet device that does not autonegotiate, disable
autonegotiation on the switch and set the duplex and flow control parameters to be compatible with
the remote device.
• 100BASE-FX ports operate only at 100 Mbps and in full-duplex mode.
• GigaStack-to-GigaStack cascade connections operate in half-duplex mode, and
GigaStack-to-GigaStack point-to-point connections operate in full-duplex mode.
• 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.
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 Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Enter interface configuration mode and the physical interface
identification.
Step 3
speed {10 | 100 | 1000 | auto| nonegotiate} Enter the appropriate speed parameter for the interface, or enter auto
or nonegotiate.
Note The 1000 keyword is available only for 10/100/1000 Mbps
ports. 100BASE-FX ports operate only at 100 Mbps. GBIC
module ports operate only at 1000 Mbps. The nonegotiate
keyword is available only for 1000BASE-SX, -LX, and -ZX
GBIC ports.