Specifications

11-11
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
78-11380-07
Chapter 11 Configuring the Switch Interfaces
Configuring Switch Interfaces
Configuring Interface Speed and Duplex Mode
The 10/100 Ethernet interfaces on the switch operate in 10 or 100 Mbps and in either full- or half- duplex
mode. The 10/100/1000 Ethernet interfaces on the Catalyst 2950T-24 switch operate at 10, 100, or
1000 Mbps only in full-duplex mode. The 10/100/1000 Ethernet interfaces on the Catalyst 2955T-24
switch operate at 10 or 100 Mbps in either half- or full-duplex mode or at 1000 Mbps only in full-duplex
mode.
In full-duplex mode, two stations can send and receive at the same time. When packets can flow in both
directions simultaneously, effective Ethernet bandwidth doubles to 20 Mbps for 10-Mbps interfaces,
to 200 Mbps for Fast Ethernet interfaces, and to 2 Gbps for Gigabit interfaces. Full-duplex
communication is often an effective solution to collisions, which are major constrictions in Ethernet
networks. Normally, 10-Mbps ports operate in half-duplex mode, which means that stations can either
receive or send.
You can configure interface speed on Fast Ethernet (10/100-Mbps) and Gigabit Ethernet
(10/100/1000-Mbps) interfaces. You cannot configure speed on 100BASE-FX, 1000BASE-SX, and
Gigabit Interface Converter (GBIC) interfaces.
You can configure duplex mode on any Fast Ethernet interfaces that are not set to autonegotiate. You can
configure duplex mode on the 10/100/1000 ports on the Catalyst 2955T-24 switch but cannot configure
duplex mode on these interfaces:
• 100BASE-FX ports on the Catalyst 2950C-24 switch
• 1000BASE-SX ports on the Catalyst 2950SX-24 switch
• GBIC ports
• 10/100/1000 ports on the Catalyst 2950T-24 switch
Note You cannot configure speed or duplex mode on Gigabit Interface Converter (GBIC) ports, but for certain
types of GBICs, you can configure speed to not negotiate (nonegotiate) if connected to a device that
does not support autonegotiation.
These sections describe how to configure the interface speed and duplex mode:
• Configuration Guidelines, page 11-11
• Setting the Interface Speed and Duplex Parameters, page 11-12
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 speed to
a non-auto value (for example, nonegotiate) and set the duplex mode to full or half to match the
device. The speed value and duplex mode must be explicitly set.