Welcome to this troubleshooting video.
This is one of multiple videos that you'll find on my YouTube channel which help you prepare for the
CCNA certification.
Now, we've been told in this topology that PC one is not able to ping PC two.
So let's do some investigation in this example.
PC one is actually an iOS router.
So I'm running iOS V with Indian as three show IP route.
Shows us that there are no routes on this router acting as a PC.
If you see output such as this default gateway is something and the IP routing table isn't displayed.
But you see something such as ICMP redirect caches empty.
It's probably because routing has been disabled on this router.
So notice this command, no IP routing that simply turns this router into an expensive, very basic
PC.
So if it was a physical router, you essentially disabling the functionality of the router can.
PC one ping.
PC two based on the information that we've been given.
As you can see in the output, it's not able to ping PC to notice we're getting you don't you don't
you you means unreachable.
That means that PC one is forwarding traffic to a router, which could be rather one.
And that router doesn't have a route to the remote network that this host resides on.
Now to speed things up, I'm going to use the command.
No IP domain lookup.
And then I'm going to trace route to 10.1 to 3.2.
So notice we are able to get to write 110 111, but rather one doesn't know where to forward the traffic.
So there seems to be a problem on rather one zone, rather one show IP interface brief.
This looks correct.
This IP address is configured on this interface.
Gigabit is error one.
This IP address is configured on this interface.
Gigabit zero zero can write a one ping router to.
The answer is yes it can.
Initial ping failed because it was doing an op for the MAC address of router two.
So let's have a look at the routing table.
Show IP route in the output, we can see that we only have connected routes and local routes.
No other routes have been learnt.
We only see Network ten 110 and Network ten 120 slash 24 and the local host addresses on the interfaces
of the router.
We don't see a network ten one three is zero.
Are we running a routing protocol on this router?
So show IP protocols shows us that we are running a routing protocol.
In this case it's OSPF process.
One router ID of the router is this it's an area border router.
It has an interface gigabit zero zero in area zero.
In other words, this network here is an area zero and this interface gigabit is zero.
One is an area one.
Show IP OSPF interface brief is another useful command.
This gives us brief information so we can see that gigabit is zero zero.
With OSPF, process one is in area zero.
We can also see the IP address and subnet mask used on that interface.
Subnet masks need to be the same.
An IP version for four routers to form a neighbor relationship.
Gigabit zero one is in area one of OSPF process one and it's got this IP address.
Show IP OSPF neighbor.
No neighbor.
Relationships have been formed.
So OSPF is running on gigabit.
Zero zero of right of one but is not forming a neighbor relationship with of two.
So let's have a look at rather two and see if we can find a problem.
Show IP protocols.
OSPF process one is running on this router and in the output.
Can you see the problem?
You should already be able to determine the problem by that output.
But I'll also use this command show ip ospf interface brief to help you.
Can you see the problem?
Notice on rata one.
This interface gigabit is zero zero is an OSPF area zero on router two.
Gigabit is zero zero is an area two.
It's a requirement in OSPF that both sides of the link be configured in the same area.
So show run interface gigabit zero zero shows us that this interface has been configured in OSPF Process
one but in area two.
Whereas on the side show run interface gigabit zero zero shows us that that interfaces in area zero.
So to fix this, we need to change the area to area zero.
So do show run interface gigabit zero zero.
Notice the OSPF area has changed.
Show IP ospf interface brief.
The area has now been set properly, show IP protocols.
Shows us now that this interface is an area zero, whereas gigabit or zero one is in area to show IP
OSPF neighbor and neighbor relationship has been established.
Now why were we not seeing output on the screen?
One of the reasons for that is that a logging could be disabled.
So do show run pipe include log.
Notice this command has been added to the running config.
No logging console.
I added that on purpose so that you didn't see warning messages on the screen to help you determine
what the problem was.
So now, as an example, if I shut down gigabyte zero zero.
Or rather should remove the no logging console and enable logging.
And now go into the interface and shut it and then no, shut it.
We should see output as in we should see that the interface comes up and there you go.
And we should see that OSPF relationships are formed.
And there you go.
Be careful of your logging if you telnet or ssh to a router.
Don't forget to use the command to monitor so that you see logging on the VI lines.
Logging is enabled by default on the console, but I had purposely disabled it, so things are looking
better.
We have a neighbor relationship show ip ospf neighbor shows us that on the side show ip is.
OSPF.
Neighbor.
Neighbor relationship is there.
Show IP route.
Notice we now see an inter area ospf route to ten 130 via ten 122.
So can this router ping the remote PC?
Yes, it can.
Can PC one ping the remote PC?
Yes, it can.
And when we do a trace, that's also successful.
Let's test in the reverse direction just to make sure everything is good.
That looks fine.
Notice the problem with traceroute.
If you don't disable IP domain lookup, the trace root is going to take a long time while it tries to
resolve the names.
So I've disabled the trace.
No IP domain.
Look up.
Do the trace again.
Notice it's a lot quicker now because it's not doing a domain lookup.
I'll do that again.
There you go.
So PC one sends traffic to router two.
And then it sends traffic to router one.
And it then hits the destination.
So that was an example of troubleshooting.
OSPF Don't forget that with OSPF you can configure it one of two ways.
You can configure it on an interface, as I've done in this example, or you can use the network command
under the writing process.
I'll leave the troubleshooting of that to a separate video.
So if you get a simulation in the exam, make sure that you check that OSPF areas have been configured
properly.
Thanks for watching.
Let me know which videos you want me to record.
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All the very best.