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Catalyst 2940 Switch Software Configuration Guide
78-15507-02
Chapter 9 Configuring the Switch Interfaces
Configuring Ethernet 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 operate at 10, 100, or 1000 Mbps. The Gigabit Ethernet
interfaces operates in 10 or 100 Mbps in either full- or half-duplex mode and in 1000 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 a Gigabit interface. 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 can configure duplex mode on any Fast Ethernet interfaces that are
not set to autonegotiate.
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 9-12
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.
• A Gigabit Ethernet port that does not match the settings of an attached device can lose connectivity
and does 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.
• 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.
• When Spanning Tree Protocol (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.
Port Fast Disabled.
Auto-MDIX Disabled.
Table 9-1 Default Ethernet Interface Configuration (continued)
Feature Default Setting