This is one of multiple videos that help you troubleshoot CCNA scenarios in preparation for the CCNA
exam.
We've been told that PC one on the left in this topology is unable to ping.
PC two.
In this topology, I'm using three and Cisco EOS V Routers.
As rather one and rather two and to mimic the PCs in the topology.
And don't trust a user when they tell you something.
As Ronald Reagan said, trust but verify.
We've been told that PC one is not able to ping PC two and we've verified that that's true.
Notice we're getting a U in the output, which means that the traffic is being forwarded to a router
and that router doesn't know what to do with a traffic.
Now to ensure that.
Traceroute runs quickly all disabled IP domain lookup and then we'll run a trace route to PC to notice
that traffic is getting to write a one but is not going any further.
So it looks like there's a problem on Ryder one.
On Router one.
Show IP route.
Shows us that the only routes in the routing table are directly connected networks and the local IP
addresses on the router.
Because this is a remote network, we need to run routing protocols on router one and router two to
exchange routes.
So router one needs to learn about Network ten 130 from router two.
So on router one, show IP protocols.
Are we running a routing protocol?
And the answer is yes, we are.
We're running OSPF.
OSPF is enabled in area zero on gigabit zero zero and in area one on gigabit zero one.
So show ip ospf neighbor.
We don't have any neighbor relationships though.
Show IP ospf interface brief.
OSPF is enabled on gigabit zero zero in Area zero and it's enabled on gigabit zero one in Area one.
So rather one looks good.
What about router to show IP protocols?
We are running OSPF on the other two, but can you spot the problem?
You should be able to see it in the output of this command to help you show IP OSPF interface brief.
Notice OSPF is not running on any interfaces on router two.
Why is that?
Look at this output.
It's routing for networks.
Ten
.1.0.000 0 to 55.
This means there's an exact match on the first three octets.
In other words, OSPF is only running on network ten 10.0.
Do we have any interfaces in that network?
Show IP interface brief.
No, we don't.
We have an IP address configured as follows and one configured as follows.
OSPF is not running on any interfaces on this router, so run pipe section ospf that allows us to view
the OSPF configuration.
So OSPF has been configured, but notice the network command has been configured incorrectly.
So router ospf one?
No.
Network ten 100.
The command should be ten 100.
002 55 255 Now you don't have to do it that way, but that's one of the options.
Notice suddenly a neighbor relationship is established.
Let's have a look at the output against the show IP OSPF interface and let's rather do a brief because
that's too much output.
Notice OSPF is now enabled on both interfaces of router to show IP protocols.
This looks a lot better.
Show IP OSPF neighbor neighbor relationship is established to write a one show IP route.
We have an inter area route en route to to network ten 110 and en route of one show ip ospf neighbor.
We have a neighbor relationship to ten 131 show IP route.
We have learnt a route through OSPF.
Now notice it's not an inter area route.
The route is in the routing table but it's showing as an intra area route.
Whereas this route is an entire area route.
Can PC one ping?
PC two Answer is yes.
So this is a decision that you would need to make based on your design.
Show IP protocols on router one shows us that OSPF has one interface gigabit is zero zero in area zero.
That's fine.
This interface is in area one.
Whereas on router two.
We have both interfaces in Area zero, so the network works, but perhaps you want to do it this way.
So rather OSPF one network ten 1 to 0 and do it more explicitly and then network ten one.
Three zero.
I'll show you the output in a moment.
If you weren't sure about what I was typing.
So show run section OSPF.
We have two network commands configured.
This network is an area zero based on this command, and this network is in area two based on this command
show, IP.
OSPF Neighbor neighbor relationship is established.
We have an internal area root on router two and on router one.
We now see an entire area root ten 130 slash 24 in other words.
This network.
Is.
In Area Zero.
This is area two.
And this is Area one.
It's important that you update your documentation and make sure that you configure your network correctly
per the documentation.
So to confirm that, show IP protocols.
This is correct.
It's area zero.
This is also correct.
That's Area one.
Show IP protocols on Ryder to.
Output looks as follows.
This network ten 1 to 0 is an area zero, and this one is an area two.
Now, the reason why we have a difference in the output.
Is notice the interfaces on router two don't have OSPF commands on them.
We enabled OSPF in the writing process using the network command, whereas on router one.
OSPF was enabled on the interfaces individually and not under the OSPF process.
Both methods work in IP version four.
In IP version six.
You need to use this method to enable OSPF on individual interfaces.
So that's an example of how to troubleshoot OSPF.
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Thanks for watching and all the very best.