Why we built this

We're network engineers. For years we kept running into the same thing at work: the people around a network — the product managers writing requirements for it, the testers verifying it, the software engineers building the tools that manage and automate it — are smart and good at what they do, but very few of them have ever seen the whole picture of how a network actually works, from the fiber in the ground up to the application on top. That's not their fault. Networking is genuinely wide and genuinely deep, and most of what's written about it is either a vendor manual or a certification cram guide. There was no single place where you could sit down for an afternoon and walk through layer 1 to layer 7 end to end.

So everyone knows their own corner, and nobody quite sees how the corners fit together. That costs real time: requirements that don't match how the protocol behaves, test plans that miss the one case that actually breaks, tools that model the network wrong and only show it in production. We've watched it happen more times than we'd like, and we've given the same whiteboard explanation more times than we can count.

Routing Lab is our answer to that. Open a browser and learn — nothing to install, no account to create. Nothing here is a diagram; every protocol is a simulation that really runs. Change a link cost, cut a fiber, add a router, and it re-converges in front of you, with the packets, LSAs, label stacks and routing tables changing step by step. We want a product manager, a tester, a developer, or a student to be able to spend a few afternoons here and come away seeing the network whole, from layer 1 to layer 7.

What's here

There are 21 modules, arranged roughly in the order a packet travels. Layer 1 first: what happens on the fiber between two data centers (OTN/ODF optical networks), and how the facilities in a region are laid out and back each other up (IDC topology). Then layer 2 — switching, STP and VLANs; layer 3 — static routing, OSPF, IS-IS, EIGRP, RIP, and eBGP and iBGP; a transport and fabric group with MPLS, SR-TE and spine-leaf data centers; applications and security — DNS, load balancing, VPN and SSL/TLS; and finally high-performance networking: RDMA and InfiniBand. Every module has a sequenced set of lessons, a few preset scenarios, a glossary and quick-reference sheet, and a short self-test.

How we'd suggest using it

Pick a module and read the first lesson. They're short, and each one answers a single question — "why does OSPF need areas?", "what actually happens the moment a fiber is cut?", "why does active-active only work within a metro?". Wherever a lesson says "try it", click it: it loads the matching scenario for you, and you can change things on the topology, break things, and watch how the protocol reacts, with the reason written next to every step. When you think you've got it, take the dozen or so questions at the end — the explanations for the wrong answers are often more useful than the lesson itself.

If you're not a network engineer, don't start with BGP. Start with Layer 2 Switching and Static Routing, then OSPF — after that you'll notice that most of what follows is the same idea showing up at a different layer.

Being honest about what this is

These are teaching models, not real equipment. The protocol behaviour is faithful enough to reason with and to teach from, and every module's core logic is guarded by dozens to hundreds of automated self-tests before it ships; but vendor-specific timing, platform quirks and performance numbers are things you only learn on real gear. What this is good at is the "why" — not replacing the switch on your desk.

Who we hope it helps

Product managers, testers and developers who work next to a network and want to finally understand it end to end; students preparing for CCNA / CCNP / HCIP who want the "why" and not just the answers; engineers who've just joined a team and need to read the company's topology by next week. It's in English and Chinese (switch in the top-right corner), it's free, and it will stay free.

If something here is wrong, missing, or you'd like a module that doesn't exist yet, tell us: isppub.com@gmail.com.