The scenario
R1, R2 and R3 are connected in a triangle by three /30 links, and each has one host network behind it: Host-A on 10.0.1.0/24 behind R1, Host-B on 10.0.2.0/24 behind R2, and Host-C on 10.0.3.0/24 behind R3. The hosts have default routes to their router; the routers have no static routes at all. Every router runs OSPF, forms an adjacency with its two neighbours, and learns the other routers' networks from them. Host-A reaches Host-B over the direct R1-R2 link, because that path is cheaper than going through R3. When you unplug that link, R1 and R2 recalculate and the traffic moves to R1-R3-R2 with no change to any configuration.
What you will work out
Understand how OSPF learns routes, picks the cheapest path, reroutes around a failed link, and why a router that stops running OSPF cuts off the network behind it.
Why this matters
Links fail, get unplugged and get cut, and a network that needs someone to edit routes every time is down until they do. Link-state protocols such as OSPF and IS-IS are how many enterprise and service-provider networks route around failures on their own. Knowing what drives the recovery time (interfaces going down, hello and dead intervals, SPF) and what redundancy cannot fix (a single router in front of a network) is the difference between designing for failure and hoping for the best.
Running it
OSPF Failure Recovery opens on a canvas, already wired and addressed. Trace a packet through it hop by hop, or run the same topology live on real Linux network namespaces. How the two modes differ.
Open OSPF Failure Recovery
Runs in your browser. No install, no signup, and the simulation starts instantly.
Open the lab →