Cisco Catalyst 2950 Command Reference Manual page 513

Chapter 2 Catalyst 2950 and 2955 Cisco IOS Commands
If the speed is set to auto, the switch negotiates with the device at the other end of the link for the speed
setting and then forces the speed setting to the negotiated value. The duplex setting remains as
configured on each end of the link, which could result in a duplex setting mismatch. If both the speed
and duplex are set to specific values, autonegotiation is disabled.
If the speed is set to auto and the 10, 100, or 1000 keywords are also used, the port only autonegotiates
at the specified speeds.
On non-Long-Reach Ethernet (LRE) switches, Fast Ethernet ports, except for 100BASE-FX ports, can
be configured at 10 or 100 Mbps. The 10/100/1000 Ethernet interfaces on the Catalyst 2950T-24,
Catalyst 2950T-48-SI, and Catalyst 2955T-24 switches operate at 10 or 100 Mbps in either half- or
full-duplex mode or at 1000 Mbps only in full-duplex mode.
You cannot configure the speed on GBIC interfaces, but you can configure the speed to not negotiate
(nonegotiate) for the 1000BASE-SX, -LX, or -ZX GBICs, if they are connected to devices that do not
support autonegotiation. GBIC-module ports support only 1000 Mbps. The speed values of 10 Mbps
and 100 Mbps are not supported.
The 100BASE-FX and SFP ports do not support the speed command. These ports operate only at 100
Note
Mbps and in full-duplex mode.
On LRE switches, LRE Gigabit Ethernet ports are set to auto by default. A copper connection
(10/100/1000) autonegotiates with the device at the other end of the link for the speed setting and then
forces the speed setting to the negotiated value. A fiber SFP connection also autonegotiates with the
device at the other end of the link but only accepts a connection at 1000 Mbps.
On LRE switches, the speed setting for a Gigabit Ethernet port has a close relationship to the setting for
duplex mode. Fiber SFP-module ports are always forced to 1000 Mbps and to full-duplex mode. Copper
ports can run in either full- or half-duplex module at 10 or 100 Mbps but is forced to run in full-duplex
mode at 1000Mbps. When you configure the speed and duplex settings, autonegotiation is disabled, and
speed and duplex settings can cause a mismatch.
The speed command is not supported on LRE interfaces. Use the
command to set the speed of individual customer premises equipment (CPE) ports.
For guidelines on setting the switch speed and duplex parameters, see the "Configuring the Switch
Note
Interfaces" and the "Configuring LRE" chapters in the switch software configuration guide for this
release.
Examples This example shows how to set a port to 100 Mbps:
Switch(config)# interface fastethernet0/1
Switch(config-if)# speed 100
This example shows how to set a port to autonegotiate the speed:
Switch(config)# interface fastethernet0/1
Switch(config-if)# speed auto
This example shows how to set a port to autonegotiate at only 10 Mbps:
Switch(config)# interface fastethernet0/1
Switch(config-if)# speed auto 10
This example shows how to set a port to autonegotiate at only 10 or 100 Mbps:
0L-10102-01
cpe speed
Catalyst 2950 and Catalyst 2955 Switch Command Reference
speed
interface configuration
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