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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 9 Configuring the Switch Interfaces
Configuring Switch Interfaces
become active. In that scenario, a valid configuration is to install the fiber-optic under Uplink Port 1 by
having an SFP module plugged in, and to install the copper under Uplink Port 2 without the SFP module
plugged in.
Note By using the media-type auto-select command in Cisco IOS command-line interface (CLI), you can
configure the Catalyst 2950 LRE so that the SFP module port does not take precedence over the
10/100/1000 port. In that scenario, whichever media type establishes a link first will have precedence
over the other.
For more information about the media-type auto-select, media-type sfp, and media-type rj45
commands, refer to the Catalyst 2950 Desktop Switch Command Reference.
Configuring Interface Speed and Duplex Mode
The 10/100 Ethernet interfaces on the Catalyst 2950 switch operate in 10 or 100 Mbps and in either full-
or half- duplex mode. (There are no 10/100 Ethernet interfaces on the Catalyst 2950 LRE switch.) The
10/100/1000 Ethernet interfaces operate in 10, 100, or 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.
On the Catalyst 2950 LRE switch, the copper media (10/100/1000) of the Gigabit interface operate in
10/100 full-duplex or half-duplex mode and 1000 Mbps only in full-duplex mode. The fiber-optic media
of the Gigabit interface only operate in 1000 Mbps and full-duplex mode.
Note You cannot configure speed and duplex on the LRE ports by normal speed and duplex commands, but
need the special local speed and local duplex commands.
You can configure interface speed on Fast Ethernet (10/100-Mbps) and Gigabit Ethernet
(10/100/1000-Mbps) interfaces on the Catalyst 2950 switch; you cannot configure speed on
100BASE-FX, 1000BASE-SX, and Gigabit Interface Converter (GBIC) module interfaces. You can
configure duplex mode on any Fast Ethernet interfaces that are not set to autonegotiate; you cannot
configure duplex mode on 100BASE-FX, 1000BASE-SX, and GBIC-module interfaces. The
10/100/1000 interfaces can operate only in full-duplex mode.
Note The speed and duplex commands are meant for copper media. The fiber-optic media always operate as
1000 Mbps with full auto negotiation no matter what has been setting for speed and duplex from the
command line. For example, you can use the command-line interface to configure the speed to be 10
Mbps and half-duplex. If the fiber-optic medium is active, then the switch attempts to perform auto
negotiation as 1000 Mbps with full autonegotiation. If the copper medium is active, then the switch
advertises as 10 Mbps and half-duplex.