CML Lab - OSPF 1

Time for me to share a problem for you to solve in Cisco Modeling Lab that aims to help solidify the trouble-shooting of OSPF in a network.

Intro:

TLDR; there a misconfiguration of OSPF on one of the routers, leading to users of PC1 not being able to ping 3.3.3.3 (R3 loopback address). Find the bug and solve it.

It was a quiet night in the network... too quiet.

Rain tapped against the server room window like a metronome counting down to chaos. Somewhere in the labyrinth of routers and cables, a mistake had been made—subtle, silent, and almost fatal. The city was humming, but R3’s loopback address? Dead silent.

Users were starting to talk. Whispers of downtime. Pings lost in the void. And all fingers pointed to a ghost in the machine—a misconfiguration buried in the shadows of a router that should’ve known better.

They brought me in to clean it up.
Preconfigured or not, something didn’t add up.
And in this line of work, every bad route has a story... and every story ends with someone getting traced.

How to get started

1. Download the .yaml file from my github: Download

2. Import it in CML, in the dashboard you can import the lab.

Good luck solving the mysterious error!

Solution [Spoiler-alert!]

Okey, are you ready?

To find the issue im sure you used some of these command:

show ip ospf neighbor
show ip ospf interface
show ip route ospf
show ip ospf database

But the most useful command in this case is show running-config | section ospf. Here you will see that the misconfiguration on R1:

R1# show running-config | section ospf
router ospf 1
 network 10.0.0.0 0.0.0.255 area 0
 network 192.168.1.0 0.0.0.255 area 1

There we have it! The 192.168.1.0 network is in area 1.

To fix the configuration:

Router(config)# router ospf 1
Router(config-router)# no network 192.168.1.10 255.255.255.0 area 1
Router(config-router)# network 192.168.1.10 255.255.255.0 area 0

Conclusion

Great work solving this issue on the network! Tricky to solve if you don’t know where to look in the first place. The show commands listed above are really handy to solve this kinds of issue.

I’m planing to release more small challenges like this one, I hope you will give them a go as well!

Are there any lab you want me to share, please give me a shout out in the comments, and I will do my best to post it here.

Until next time,
Cheers!