This is one of a multiple plan or local area network troubleshooting videos.
In this video we have four switches running ingenius three switch one and switch two are configured
as layer three switches switch 3 and switch for configured as lead to 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 away Sivi lead to.
And what I've done is simply disable IP routing on switch 3 and switch 4.
So we have four switches in the topology and two Iowas V-Rod is Rato one and Rodek to acting as PCs.
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-connect.
I'm not going to do that in the trouble shooting video.
Have a look in my CCN a course which is linked below for a more complex topology running HAARP optimized
spending tree redundancy between the call and the access layer and multiple other options that 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 a network connectivity issues.
You've been told that to this user 10 1 to 1 in violent 2 he's unable to ping the fuse that has a PC
with IP address turned off one or two 1:57 in the villa and three you've been told that switch three
is connected to switch one as follows.
So which one is connected to switch to and switch to 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 typology a one he's acting as PC one 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 at 1 2 3 2 2 which is the IP address of router to acting as PC to.
OK 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 ROFFT shows us no routes in the writing table but it shows us that the default gateway is set
to 10 not 1 2 2 5 4.
Now that's because IP routing has been disabled on this router in the apology we've got one acting as
a PC.
So when IP routing is disabled this is what the writing table looks like.
The default gateway has been configured on the PC 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 telling that to the right IP address.
So the device is there but we are told that a password is required but none is set.
So hopefully the default gateway and this typologies either switch one or switch to which all of the
call three switches so which one show IP interface brief we can see that villain one violent turn violent
three have an IP address configure.
And that's the IP address on the land too.
So those should be the device that the PC is pinging.
I'll do a debug IP ICMP on that switch and get the pc to ping the default gateway.
Now you need to be careful with debugging in a real world environment.
Yeah because we studding for the CCMA we can simply enable any debug command because that'll help you
learn the debugs 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 all 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.
OK so the pings do arrive on this default gateway so that's good.
I'm going to turn off IP domain look up in the lab here to make things happen quicker.
And then what we'll do is trace 10 one or two three to two which should be PC to not apology.
Let's see how far it gets.
So it gets to the default gateway which we've now determined the switch one.
So what we should do is update the documentation so we could say that these are the IP addresses on
the villans 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 route shows us that the traffic gets to the default gateway but then doesn't go anywhere as
let's check if PC to ping its default gateway.
Now a test I like to do is to make sure that the local device can paying the other villain of the default
gateway.
So in other words the PC is in veel and two it's in submit 10 1 2 0 and I'm checking that it can ping
the subnet of the device that we try 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 routing is working on the last three switch but now let's
check the connectivity of PC to can it get to its default gateway.
So this is Rodda to acting as PC to show IP interface brief IP address looks right per the diagram subnet
mask looks right now that information is once again not shown in the diagram.
So we'd want to add that somewhere and you may want to add that on individual devices or make a note
some way that the subnets have a flash 24 mosque show IP wrote shows us the default gateway of PC to
so Kennet ping its default gateway.
No it can't.
So there's something wrong either here or here.
Or let's have a look at Switch for switch forwards the local access switch show Oppy interface brief.
It has an IP address of 10 1 1 4th can it paying such one in villaine one.
Yes it can show IP Raat default gateways tendered one does wonder too far for Kennet paying $10.
One but three to five four yes it can kinda ping the PC in the villa and three.
No it can't.
So the switch kipping the default gateway into Fillon routing is working on the default gateway but
it can ping the PC traffic from the switch to this PC you'd have to traverse to here to get to the default
gateway and then it would have to come back again.
That'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 to 0 0 is up.
Which is the link to the core network pings that were previously so.
So we have an indication that those interfaces are already up and working.
Interface trunk is 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 violent 3 Can you see the problem in the south.
Put into face name is gigabit.
0 1 it's enabled us to switch port administer of moders dynamic order.
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 trunking with.
Notice the problem access mode villain is one show run interface Gieger bitches are one the sport is
not in villaine three
interface gigabit.
0 1 is currently in Villon 1.
So switch port access land 3 show interface gigabit to 0 1 switch port Port is now an access port in
villans 3 show run interface gigabit to 0 1.
There's our configuration.
Let's check if the local switch can ping that PC at the moment it still can't.
It may take a while for spending tree and other protocols to converge.
So you may just need to wait a bit before you see that there's a problem but spanning tree at this point
looks good.
So it shows GDP neighbors.
We can see that rodded to he's connected to Gigabit 0 1 using gigabit 0 0 show interface gigabit to
0 1 switch port confirms that the port is in violent three.
So let's go back onto the PC 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 has made any
difference.
Kennet paying wrote a one acting PC one.
Yes it can.
So it looks like we've solved the problem.
We could trace to the PC 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 layer two issues but remember to check your interfaces
check your villans check your encapsulations and other videos.
I will show you all the problems that you may encounter.
I need to troubleshoot this topology.
Ok enjoy this video.
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I wish you all the very best.