Original subtitles

Duplex and speed negotiation is also important for connections between a PC and a switch.

in this example the PC is connected to the switch using this interface Ethernet 2

at the moment the speed negotiated is 100 Mbps.

so here’s the switch, sh int f1/0/5

this interface is currently running at full duplex 100 meg on the switch

and that’s what been negotiated on the PC, so we can see 100 Mbps.

now we could change some of these settings on the PC.

So if we wanted to, we could change the speed and duplex negotiation at the moment using

auto negotiation but we could make a mistake and set it to 1 gigabit per second full duplex. 10

On the switch we see that the interfaces gone down, it’s supposedly come up again 11

so I'll just look at the duplex and the output. 12

The switch is using 100 meg full duplex and on the network card 13

it's actually moved down to 100 meg rather than using the gigabit speed 14

that we configured but if the PC had accepted that speed of 1 gigabit per second 15

full duplex we would have a duplex and speed mismatch 16

between the switch and the PC which would have caused problems. 17

Let’s set the PC to 10 meg and see if they can still negotiate properly. 18

So interface has gone down, it's come up and in this case it has negotiated properly. 19

In gigabit Ethernet even when set manually the device will still tell the other side 20

what speed and duplex it's using. 21

So things are a lot better than they were in the past. 22

Let's set the side for auto negotiation 23

but what I’ll do now is on the switch configure it manually. 24

so interface F1/0/5 25

do sh run int f1/0/5 duplex and speed are not set 26

but let's set the speed to 100 meg duplex to full. 27

So the configuration looks as follows interface has come up 28

what is the side using? It’s using 100 Mbps. 29

so do sh int f1/0/5 type include duplex that looks good. 30

Let's set the duplex to half and the speed to 10. 31

On this side negotiation has taken place successfully. 32

So things are a lot better than they were years ago 33

with duplex and speed but generally the recommendation is to use 34

Auto negotiation of speed and duplex, allow both sides to negotiate 35

to the highest speed and duplex that they both support. 36

So I’ll try and break this by going to the 100 full duplex. 37

Interface is going down and come up but it's still successfully negotiated 38

so it's still showing speed of 10 meg. 39

Let’s however configure it to go to the best possible speed and duplex. 40

So I’ll set it to use auto negotiation and on the switch. 41

Well set this, speed to auto, duplex to auto 42

and as we can see sh int f1/0/5 include duplex. 43

The output shows full duplex 100 meg 44

so it has successfully negotiated with the PC to use 100 meg full duplex. 45

So in summary again auto negotiation is the way to go today 46

if you are gonna hard-code, make sure that you hard-code correctly on both sides.