A number of years ago I had a customer who had a connection from the head office to a data center in
London and they raised a ticket stating that the connection to the datacenter was very slow.
They were connecting to a router with a VPN to the data center and throughput was very poor.
In other words they could ping the data center without any problems.
But when they sent large files the connections were very very slow.
I went to site and on investigation I found that there was a duplex mismatch between a Cisco router
and a Cisco switch duplex mismatches used to cause a lot of problems in the past.
The negotiation of Duplaix often failed on 10 one hundred links.
And in those days it was recommended that you hard code speed and duplex on links between devices such
as Cisco routers and switches today fortunately things are a lot better today it's generally recommended
that you allow switches and routers to use auto negotiation of duplex as well as speed.
Now in some cases you may want to hard code at the speed and duplex between your switches and your routers
but be aware that if you configure it incorrectly you may end up with an issue such as the following.
Notice the switch is stating that there is a duplex mismatch on fossa.
Ethan it is 0 4 to another switch on Fosset Ethernet 0 4 on the router.
We have a duplex mismatch on FASA Ethan and 0 to the switch on fossa.
Ethan it is 0 3 in this video.
I'm not using Jeana's 3 I'm using physical switches and I'm simply using genius 3 to show you what the
topology looks like.
I have two routers each in turn connected to 29 50 switches which are connected to 750 switches and
I have a laptop connected on port 0 5 to the first 30 750 switch.
So let's have a look at some of the issues you may encounter with Duplaix mismatches.
Remember that with full duplex a device can transmit and receive at the same time.
Whereas with half duplex only one side can send in other words a device cannot send and receive simultaneously
with half duplex one party transmits and one party receives with full duplex.
Both parties can transmit and receive at the same time half duplex was required for connections to hubs
these days because of the use of Ethan switches.
We generally want to use full duplex which means as an example on this 100 megabits per second link
the switch can send traffic to the course which at 100 megabits per second and at the same time the
cost switch can send traffic to the 29 50 switch at 100 megabits per second.
So we actually have a throughput in theory of 200 megabits per second 100 in each direction when using
full duplex now cabled the link here to show you a problem with Duplaix between two 29 fifties.
And I'll also demonstrate Orta negotiation of speed and duplex between thirty seven fifties and 29 50s
as well as a PC and a switch.
But before we do that let's have a look at some of the problems you may encounter when you have a duplex
mismatch.
As mentioned your throughput may be a problem.