$ CCNA LABS // break-fix
Inherit a broken network. Work the ticket.
Six troubleshooting labs on the five-node base topology. Each one boots straight into its broken state, hands you a symptom, and makes you find the cause on real Cisco IOS XE.
The first lab is free with no signup. Pro unlocks the other five and the whole library.
The CCNA Labs teach you to build a network from a blank config. These labs do the inverse. You get a support ticket that describes a symptom and nothing else, and your job is to localize the fault and fix it. That is the skill the CCNA 200-301 hands-on items lean on hardest, and the one most study material skips. Every fault was injected into a live CML topology, captured broken, then fixed and captured again, so the output you read is the output you will see.
How a lab runs
Each lab is a small ticket queue. Import the topology, start it, and work the tickets in order. A ticket gives you the symptom in the user's words and one success criterion. It does not tell you the cause. You reproduce the symptom, climb the OSI stack until a command contradicts what you expect, fix it, and verify. After each ticket the lab shows the root cause and the exact fix so you can check your work.
Because the topology is small, faults mask one another, exactly as they do on a real network. The method that beats this is always the same: work bottom-up, fix the lowest layer or most upstream problem first, and re-test before moving on.
The shared topology
Three routers (R1, R2, R3), one managed switch (SW1), one host (HOST1), and an unmanaged switch (SW2). R1 and R2 share the LAN 10.20.0.0/24 through SW1; R2 reaches R3 over the point-to-point link 10.30.30.0/30; each router carries a loopback. Same IP scheme and same pinglabz / PingLabz!23 credentials as the rest of the library, and it fits inside CML Free.
The six labs
Where this fits
Configure a feature in the CCNA Labs, then come here to practice fixing it when it breaks. Each troubleshooting lab names the build labs it assumes. If you want the general method first, build lab nf-11 Troubleshooting Layer Symptoms teaches the seven-step escalation drill this whole series relies on. When you are ready to build an entire campus from scratch, sit the CCNA Mega Lab.
Protocol deep-dives for the same failures
The labs above are timed ticket practice. These are the reference articles to read when you hit the same failure on a real network and need the mechanism rather than the drill. All free.
Frequently asked questions
Do I need a paid CML license?
No. Every troubleshooting lab uses the five-node base topology and fits inside Cisco Modeling Labs Free. Import the lab's .yaml, start it, and it boots into the broken state.
How are these different from the build labs?
The build labs hand you a goal and a blank slate: configure VLANs, configure OSPF, configure NAT. These hand you a broken network and a ticket. Same topology, same IP scheme, opposite skill.
Which lab should I start with?
The free ts-nf-01 Connectivity Tickets. It teaches the bottom-up method every other lab in the series relies on. Then work up through the pillars to the capstone.