Original subtitles

This is one of a multiple land or local area network troubleshooting videos.

In this video we have four switches running ingenious three switch one and switch two are configured

as Layer three switches switch three and switch for configured as Layer two switches so I could change

the symbol as an example

to indicate that that's a layer to switch however these four switches are running.

IOW a v layer to

and what I've done is simply disable IP running on switch three and switch four.

So we have four switches in the topology and two Iowa's v Rogers right a one and write it to acting

as pieces.

This is a very simple topology where we have a core and an access layer.

Typically you would connect the core to the access layer using cross connects.

I'm not going to do that in this troubleshooting video.

Have a look in my CCN a course which is linked below for a more complex topology running HSR P optimized

spanning tree redundancy between the core and the access layer and multiple other options.

But this network will suffice for our basic troubleshooting.

So now let's assume that a new hire has made some configuration changes on the network and users are

complaining about network connectivity issues you've been told that to this user 10 1 to 1 in VLAN 2

is unable to ping this user that has a P.C. with IP address 10 dot 1.0 3 or 2 in V land 3.

You've been told that switch 3 is connected to switch 1 as follows.

So each one is connected to switch 2 and switch 2 is connected to switch for but as Ronald Reagan said

Trust but verify.

And what I like to say is don't trust anything that you've been told about a network until you've checked

it yourself.

So you're not topology right a 1 is acting as P.S. 1 show IP interface brief shows us the IP address

on the gigabit interface that looks right the IP address looks right subnet mask looks right.

Let's see if we can ping 10 but wonder 3 or 2 which is the IP address of Rada t acting as P.S. To

Okay so the ping is failing we don't seem to be able to ping that device so that piece of information

is true.

Show IP rot shows us no roots in the routing table but it shows us that the default gateway is set to

tend on 1 2 2 5 4.

Now that's because IP routing has been disabled on this Radha in this topology we've got Radha one acting

as a P.C. so when IP writing is disabled this is what the writing table looks like.

The default gateway has been configured on the P.C. so that's good.

Let's check if we can ping the default gateway yes we can.

Now where is the default gateway.

We could try and Telnet to the default gateway

and let's try and Telnet to the right type of address so the device is there.

But we're told that a password is required but none is set.

So hopefully the default gateway in this topology is either switch one or switch to which all of the

core Layer 3 switches.

So here's switch one show IP interface brief we can see that a villain one villain tune villain 3 have

an IP address configured and that's the IP address on VLAN 2.

So this should be the device that the P.C. is pinging.

I'll do a debug IP ICMP on that switch and get to the P.C. to paying the default gateway.

Now you need to be careful with debugging in a real world environment.

Yeah.

Because we studying for the CCMA we can simply enable any debug command because that'll help you learn

the debug that are available but in the real world.

Be careful with simply enabling a debug especially on a core device.

You may get so much output on the console that you can't read anything or in a very bad situation the

device may fall over so we don't want that.

So in the real world.

Be careful with debugging.

Okay so the pings do arrive on this default gateway so that's good.

I'm gonna turn off IP domain look up in the lab here to make things happen quicker.

And then what we'll do is trace tendered one dot three or two which should be P.C. to an auto apology.

Let's see how far it gets.

So it gets to the default gateway which we've now determined is which one.

So what we should do is update the documentation so we can say that these are the IP addresses on the

V lands of that switch.

That once again can be seen on switch one by using the show IP interface brief command and there they

are once again

the trace rot shows us that the traffic gets to the default gateway but then doesn't go anywhere else.

Let's check if P.S. two components default gateway now a test I'd like to do is to make sure that the

local device can ping the other VLAN of the default gateway.

So in other words this P.C. is in Vila and 2 it's in subnet 10 1 2 0 and I'm checking that it camping

the subnet of the device that we're trying to go to but this is the IP address of the default gateway

into that villain.

In other words we've proven that interval and writing is working on the layer 3 switch but now let's

check the connectivity of PCI 2 can it get to its default gateway.

So this is rather to acting as P.C. to show IP interface brief IP address.

Looks right.

Per the diagram subnet mask looks right now that information is once again not shown on the diagram.

So we'd want to add that somewhere and you may want to add that on individual devices or make a note

somewhere that these subnets have a slash 24 mask show IP run it shows us the default gateway of PCI

2 so cannot ping its default gateway No it can't so there's something wrong.

Either here or here or here let's have a look at switch for switch forwards the local access switch

show IP interface brief it has an IP address of 10 1 1 4 can it paying such 1 in VLAN 1 yes it can show

IP wrought default gateways tendered 1 1 2 5 4 can it paying tendered 1 dot 3 2 5 4 yes it can can it

ping the P.C. in the violent 3 No it can't so the switch camping the default gateway into V Line routing

is working on the default gateway but it can't ping this P.C. traffic from the switch to this piece

you would have to traverse to here to get to the default gateway and then it would have to come back

again let's confirm the ports on switch for so firstly show IP interface brief let's confirm that interfaces

are up all interfaces look up including gigabit 0 1

that interfaces up gigabit 0 0 is up which is the link to the core network pings that were previously

so so we have an indication that this interfaces are ready up and working.

Show interface trunk there's a trunk to the core on gigabit 0 that looks good let's have a look at the

gigabit.

0 1 interface show interface gigabit 0 1 switch port this interface should be in villain three.

Can you see the problem in the this.

Put interface.

Name is gigabit 0.

It's enabled as a switch port administrative mode is dynamic auto.

It's currently acting as a static access port so dynamic trunk protocol or DTP did not negotiate to

form a trunk so DTP is on but there wasn't a switch to negotiate drinking with noticed the problem access

mode.

A villain is one show run interface gigabit to 0 1 this port is not in VLAN 3.

Interface gigabit 0 1 is currently in VLAN 1.

So switch port access.

Vigeland 3 show interface gigabit.

0 1.

Switch port Port is now an access port in VLAN 23 show run interface gigabit.

0 1 There's a configuration.

Let's check the local switch can ping that P.C. at the moment it still can't.

It may take a while for spanning tree and other protocols to converge

so you may just need to wait a bit before you assume that there's a problem but spanning tree at this

point looks good.

So show CTP neighbors we can see that right it to is connected to gigabit 01 using gigabit 00 show interface

gigabit 01 switch port confirms that to this port is in V land 3 so let's go back on to the P.C. and

check if it can ping its default gateway.

It can now.

So once again you may just have to wait a little bit before you assume that your change hasn't made

any difference Kennett paying

a one acting as P.S. 1.

Yes it can.

So it looks like we've solved the problem

we could trace to the P.C. which didn't work before that now works.

So previously when we traced to 10 1 3 2 it failed at the default gateway but now it's working and we

could do a ping to prove it.

And do a debug on the side to prove that the traffic arrives so that was an example of how to troubleshoot

a local area network it can sometimes be complicated to troubleshoot a layered two issues but remember

to check your interfaces check your v lands check your encapsulation as in other videos.

I will show you other problems that you may encounter and need to troubleshoot in this topology open

joint of this video.

If he did please like it.

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I wish you all the very best.