Although the configuration of speed and duplex is incredible easy, the concept behind them is somewhat important.
Duplex defines how traffic will be sent and can be related to a 2-way radio vs. A telephone.
With a 2-way radio, more so when there are more than 2 people on the same radio frequency, only 1 person may speak at the same time. If 2 people were to push the PTT (push to talk) button at the same time, they would hear a squelch. Both people would hear the squelch, release the PTT button and try again at a random time interval. Hopefully only 1 person would press the button this time and would be able to speak on the radio frequency, of course if both people pressed the button at the same time again, they would have to repeat the procedure until they managed to be the only person communicating.
In terms of Duplex, a 2-way radio would be the same as ‘Half-Duplex’ were only 1 person may communicate at the same time, if computers tried to talk at the same time, they would have a ‘collision’. Like the people, the 2 computers notice the collision and wait a random time frame before transmitting the packet again.
Full duplex on the other hand is like a telephone. Both parties in a telephone call can talk at the same time. Granted most humans cannot hear and talk at the same time on the phone, but the telephone is able to transmit both flows of traffic from both sides of the telephone line at the same time. If 2 computers wished to send data to each other, and full duplex was available, they would be able to transmit and receive at the same time.
NOTE: A hub can ONLY run at half-duplex. It is not possible for a hub to run at full duplex. A Switch however can be configured for either.
AOIP.ORG_Switch# show interface f0/7
In the live demo below you will notice I have highlighted the current status of the interface (Auto-duplex, Auto-speed)
AOIP.ORG_Switch# conf t
AOIP.ORG_Switch(config)# interface fastethernet 0/7
Enter the interface you wish to configure
AOIP.ORG_Switch(config-if)# duplex full
Set the Duplex to Full, Half or Auto. Auto doesn’t always end up with the best result, so forcing the duplex to the correct value to recommended
AOIP.ORG_Switch(config-if)# speed 100
Set the speed of the interface. Depending on the interface will depend on the possible options. Ethernet can only be set at 10Mbps, FastEthernet can be set at either 10Mbps or 100Mbps, and GigabitEthernet can be set to 10/100/1000 mbps
AOIP.ORG_Switch(config-if)# no shut
Activate the interface
AOIP.ORG_Switch(config-if)# do show interface f0/7
Confirm the new setting have taken effect.
Here is the live demo.