Configuring Interface Speed And Duplex Mode; Configuration Guidelines; Setting The Interface Speed And Duplex Parameters - Cisco WS-C3550-12G Software Configuration Manual

Configuring Layer 2 Interfaces

Configuring Interface Speed and Duplex Mode

These sections describe how to configure the interface speed and duplex mode:
•
•

Configuration Guidelines

When configuring an interface speed and duplex mode, note these guidelines:
•
•
GigaStack-to-GigaStack cascade connections operate in half-duplex mode, and
Note
GigaStack-to-GigaStack point-to-point connections operate in full-duplex mode.
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

You can configure interface speed on Fast Ethernet (10/100-Mbps) and Gigabit Ethernet
(10/100/1000-Mbps) interfaces; you cannot configure speed on Gigabit Interface Converter (GBIC)
interfaces. You can configure duplex mode on any Fast Ethernet or Gigabit Ethernet interfaces that are
not set to autonegotiate; you cannot configure duplex mode on GBIC interfaces. Because collisions are
major constrictions in Ethernet networks, full-duplex communication is an effective solution. Normally,
10-Mbps ports operate in half-duplex mode, which means that stations can either receive or send. 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.
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.
Catalyst 3550 Multilayer Switch Software Configuration Guide
8-14
Configuration Guidelines, page 8-14
Setting the Interface Speed and Duplex Parameters, page 8-14
If both ends of the line support autonegotiation, we highly recommend the default autonegotiation
settings.
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.
Chapter 8 Configuring Interface Characteristics
78-11194-03