
10-13
Catalyst 3550 Multilayer Switch Software Configuration Guide
78-11194-09
Chapter 10 Configuring Interface Characteristics
Configuring Ethernet Interfaces
Configuring Interface Speed and Duplex Mode
Ethernet interfaces on the switch operate in 10, 100, or 1000 Mbps and in either full- or half-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 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.
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 10-13
•
Setting the Interface Speed and Duplex Parameters, page 10-14
Configuration Guidelines
When configuring an interface speed and duplex mode, note these guidelines:
•
If both ends of the line support autonegotiation, we highly recommend the default setting of
autonegotiation.
•
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.
•
100BASE-FX ports operate only at 100 Mbps in either full- or half-duplex mode and do not support
autonegotiation.
•
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.