Configuring the Port Speed and Duplex

Configuring the Port Speed and Duplex
By default, all 10/100 ports on the 2950, 3550, and 4000 are set to auto-detect the speed and
duplex of the port.
4000 Series Set-Based Switch
Because the ports on a 10/100 card are auto-detect, you don’t necessarily have to set the speed
and duplex. However, there are situations where the auto-detect does not work correctly, and
by setting the speed and duplex, you can stabilize the link:
Terry_4000> (enable) set port speed 2/1 ?
Usage: set port speed <mod_num/port_num> <4|10|16|100|auto>
Terry_4000> (enable) set port speed 2/1 100
Port(s) 2/1 speed set to 100Mbps.
If you set the port speed to auto, both the speed and duplex are set to auto-negotiate the link.
You can’t set the duplex without first setting the speed:
Terry_4000> (enable) set port duplex 2/1 ?
Usage: set port duplex <mod_num/port_num> <full|half>
Terry_4000> (enable) set port duplex 2/1 full
Port(s) 2/1 set to full-duplex.
Terry_4000> (enable) ^C
Notice that the command Ctrl+C was used in the preceding code. This is a break sequence used
on both types of switches.
You can view the duplex and speed with the show port command:
Terry_4000> (enable) show port 2/1
Port Name Status Vlan Level Duplex Speed Type
----- ------------- ---------- ----- ------ ------- ----- -----
2/1 Sales Printer notconnect 2 normal full 100 10/100BaseTX
Connecting and Logging In to a Switch 437
2950 and 3550 Switches
You can configure multiple options on any port. Speed can be set to 10, 100, or auto, and duplex
can be set to half, full, or auto. You cannot configure duplex to full if the speed is set to auto. Here
is an example from a 2950:
Terry_2950(config)#int fa0/1
Terry_2950(config-if)#speed ?
10 Force 10 Mbps operation
100 Force 100 Mbps operation
auto Enable AUTO speed configuration
Terry_2950(config-if)#speed 100
Terry_2950(config-if)#duplex ?
auto Enable AUTO duplex configuration
full Force full duplex operation
half Force half-duplex operation
Terry_2950(config-if)#duplex full
Terry_2950(config-if)#^Z
Terry_2950#
Terry_2950#sho int fa0/1
FastEthernet0/1 is down, line protocol is down
Hardware is Fast Ethernet, address is 000b.be53.2c01 (bia 000b.be53.2c01)
Description: Finance_VLAN
MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/s