I built Peerfall: learn FRRouting through a browser game

Part 2 of Learn by Breaking Things. Part 1 · Kernelfall

Router A can send a ping all the way to router C. C receives it. A still reports 0 received. Where would you look next?

That’s a mission in Peerfall, the open-source game I’m building to learn FRRouting. Kernelfall started with a command and followed it into the Linux kernel. Here I wanted to follow a packet across a network and see what happens when it gets stuck.

Play Peerfall on desktop · Source on GitHub

Try one mission

In The Reply That Never Came Back, router A sends a ping to C through B. After it times out, switch to C and run nstat -az IcmpInEchos IcmpOutEchoReps. The first counter shows requests arriving. The second shows no replies going out. Does C have a route back to A? Mission source

Peerfall boots Linux in the browser using v86, the same emulator I used for Kernelfall. The routers run FRR, so you can inspect routes in vtysh and check how Linux will forward a packet with ip route get. Peerfall architecture

Peerfall is still in development. If you’re new to FRR, start with The Dark Cable and tell me which instruction made you reach for a hint. If you work with FRR and have an outage you think would make a good mission, I’d love to hear how you diagnosed it. Open an issue on GitHub