Yes rather one which is this device and I'll ping router two from router one to see if ping succeed.
So ping ten 112 pings succeed.
But notice we are getting a message that there's a duplex mismatch between the router and the 2951 switch.
So we've been told that there's a duplex problem here.
And on the switch we're seeing that there's a duplex mismatch on fast Ethernet 203 to the router.
So we've been told that there's a duplex problem here, but we're also told that there's a duplex issue
on Fost Ethernet zero four.
To the 2952 switch on Fast Ethernet zero four.
So there's a problem here as well.
Now you may not be physically connected to the console and hence you may not see these issues.
That's a good reason to use a syslog server or a management application from a company such as SolarWinds.
So let's ping rather to.
Again, Ping succeeds.
So pings aren't necessarily a good way to test for duplex mismatches.
However, I'll do an extended ping to.
That rather.
So let's try that again.
Ten one, one, two.
I'll send a thousand pings and I'm going to make the data gram size a large size.
So we want to send a lot of traffic onto the network and hopefully we'll encounter a problem.
And there you go.
We've got a message saying a late collision has occurred.
So this is a problem you may encounter.
One side may tell you that there are late collisions, as you can see over there.
We're getting a number of late collisions.
On the other side, we're not seeing that.
So on the switch show interface if 0/3.
We're not seeing a lot of elite collisions.
The configuration of that interface is set to a speed of ten meg and duplex of full.
But notice on this side show run interface f zero.
The side has its speed set to 100.
Let's confirm that show interface f is zero.
Notice the duplex is half.
Speed is set in this example to ten megabits per second.
So the router because it can't negotiate properly with the other device, in this case, the 2950 switch
has set its speed to a value of ten meg of duplex.
So the point to remember is when there is a mismatch, the side that is set for half duplex.
We'll see a late collisions on the connection.
But this only occurs when you sending enough traffic.
So extended ping doesn't show that problem.
But when a large amount of traffic is sent on this half duplex connection, we're getting a late collisions.
On the switch side show interface if 0/3.
Notice the speed is full duplex, ten megabits per second, whereas on the router it's half duplex ten
megabits per second.
Even though I configured it to use 100 megabits per second, it's using a fail back position of the
worst case scenario, which is ten meg of duplex.
And in this case, we're having that problem.
Notice this is 100 based TCF, whereas this side is 100 based TCS.
So in this example, the router has gone for half duplex ten megabits per second, whereas the switch
is using ten meg full duplex and hence we've got a duplex mismatch.
So in summary, we get told by CDP that there is a duplex mismatch.
The local interface is not using full duplex, whereas the other side is using full duplex.
Pinging a device doesn't tell us that there's a problem, but when large packets are sent.
User's main counter drops.
Poor throughput and you may see late collisions.
So let me saturate that link again.
Send 1000 pings, large data, gram size.
Show interface f0/3.
Notice we are now seeing the late collisions taking place on the interface.
So on the half duplex side.
We see this output of late collisions on the interface show interface zero.
Notice the number of late collisions is increased.
On the full duplex side, we may get input errors such as CRC errors or runt frames.
So in this example, we've got 28 input errors, 15 crosses.
We aren't seeing any runs, but we are receiving duplex mismatch messages.