About Faultline
What is Faultline?
Faultline is a hands-on network troubleshooting platform. Every lab spins up real Docker containers running an IOS-style CLI, injects a genuine fault into the topology, and grades your fix by testing live network behaviour — not by comparing your commands to a stored answer key.
Is Faultline affiliated with Cisco?
No. Faultline's CLI mimics Cisco IOS syntax because that's the vendor-neutral language most networking courses — and the CCNA/CCNP exams themselves — already teach in. Faultline isn't made by, endorsed by, or affiliated with Cisco Systems in any way.
Why is it called "Faultline"?
A fault line is where pressure builds until something breaks — that's every lab here: a network that was working, until it wasn't, and it's on you to find where.
Do I need any networking hardware or software installed?
No. Every lab runs on real containers on Faultline's own infrastructure, and you interact with them entirely through your browser. Nothing to install, no vendor images to download, no lab kit to buy.
Labs & grading
How is my work actually graded?
When you submit, Faultline runs deterministic probes — real pings, real show command output, real routing table checks — against the live containers your commands actually configured. Nothing is compared against a stored answer key, and no AI or language model is involved in grading at any point. See "How grading works" from inside any lab for the exact detail.
Is there more than one way to solve a lab?
Yes, deliberately. Grading checks the resulting network behaviour — does the ping succeed, does the route appear, is the adjacency up — not a specific sequence of commands. Two people can solve the same lab completely differently and both get full marks.
What's the difference between Guided, Troubleshoot, and Memory labs?
Guided (Lab 1) walks you through building a configuration step by step, with a "Why" box explaining what each command does. Troubleshoot (Lab 2) drops you into a topology someone else broke and asks you to find and fix it, like a real ticket. Memory (Lab 3) gives you the objective only — no steps, no hints — so you can prove you can do it unassisted.
What is NOC mode?
NOC mode frames the same real labs as incoming tickets in a simulated Network Operations Centre inbox. A "customer" reports a symptom, you investigate the actual broken network behind it, and the ticket resolves once your fix is verified live — not when you click a button that says you're done.
Do lab sessions expire?
Yes — each session has an idle timeout, shown as a countdown once you're in a lab, so containers aren't left running indefinitely. Any command you run resets the timer, and you'll get a warning before it closes.
Getting started
Do I need an account to try a lab?
No — every lab today is free to try with no sign-in at all. Accounts, progress that follows you across devices, and billing are coming; see the Roadmap.
Which tracks does Faultline cover right now?
CCNA is the most built-out today, with a full course covering addressing, VLANs, trunking, EtherChannel, spanning tree, routing, NAT, DHCP, NTP, ACLs, and Layer 2 security. CCNP exists as standalone labs today, with a fuller course structure on the way.
Is EIGRP supported?
Partly, and it's worth knowing where the edges are. EIGRP runs on a real routing daemon here like every other protocol — real adjacencies, a real composite metric, real routes at administrative distance 90 — so router eigrp, network (both the classful and wildcard-mask forms), eigrp router-id, variance, maximum-paths, metric weights, redistribute, the per-interface hello and hold timers, and show ip eigrp neighbors / interfaces / topology all do what they do on real kit.
Three commands the exams teach are not modelled: auto-summary / no auto-summary, eigrp stub, and passive-interface. The open-source EIGRP daemon Faultline is built on either doesn't implement them or rejects them outright, and rather than accept the command and quietly do nothing, the CLI tells you it isn't modelled and why. That's the rule everywhere in Faultline: a command either does something real or says it doesn't — you'll never type something that silently pretends to work.
There are no EIGRP labs yet. The protocol works if you configure it yourself in any lab that gives you routers; a dedicated set of EIGRP labs is on the list.
What if I get stuck?
Guided labs have their own step-by-step walkthrough with a "Why" box on every command. Troubleshoot and Memory labs intentionally don't hand you the fix — but Troubleshoot labs do outline the real methodology (which show commands to check, what to compare) without naming the actual fault, the same way a senior engineer would point a junior one in the right direction.
Support & what's next
I found a bug, or have a suggestion.
Get in touch — see the Contact page. Faultline is actively being built, and real feedback shapes what gets built next.
What's coming next?
Additional vendors beyond Cisco IOS, real Linux VMs in the topology, CCIE-level content, and the ability to build and share your own labs are all ideas in progress — see the full Roadmap for details.