What will you learn?
Start with three routers and a destination network, then change one setting or break one link at a time. You will learn to explain the result before checking the commands. By working through the lessons, you can:
- Explain how Hello packets discover neighbours and when those neighbours form a full adjacency.
- Read link-state advertisements, follow their flooding scope and calculate a path using interface costs.
- Configure single-area OSPFv2, passive interfaces and default-route advertisement, then verify the result.
- Compare network types, DR/BDR elections, multi-area designs, authentication and special area types.
- Investigate a failed adjacency or missing route using evidence, then confirm the repair.
Course at a glance
29 learning pages in 6 modules, including 4 labs, 1 course test and a reference sheet. The format combines written explanations, labelled diagrams, command examples, interactive exercises and quizzes. The basic configuration lessons use Cisco IOS-style syntax; each lab describes its starting conditions.
Choose a lesson from the menu on the right on desktop, or expand Course contents above the page on mobile. The links below explain where to start; the menu gives you the complete lesson list.
Start with the OSPF overview →
Before you start
You do not need previous OSPF experience. You should be comfortable identifying an IPv4 subnet, reading a routing table and explaining an interface and a next hop. If those ideas are new, work through IP addressing and the routing basics first.
You can read the explanations and use the page exercises without a router. For the configuration labs, prepare an isolated router environment with the features required by that lab. Command examples show what to configure and check; interactive page exercises practise specific decisions rather than emulate an entire router.
How OSPF fits together
A link-state advertisement (LSA) describes routing information. Routers exchange these records to build a link-state database (LSDB). Within an area, synchronised routers share the area’s topology information, but each calculates paths from its own position. Having the same map does not mean having the same next hop.
Neighbour discovery, database synchronisation and packet forwarding are different jobs. A Full neighbour is useful evidence, but it does not prove that a user can reach a server. You must also check the destination route, the return path and the hosts’ settings.
OSPF also maintains its information while the network is stable: Hellos continue and LSAs are refreshed. The operation lesson distinguishes those messages from updates caused by a topology change.
Find your learning path
Begin with the routing problem
Follow a failed link and ask which router needs new information. Why networks need OSPF explains the problem with maintaining static routes. Then how OSPF works connects neighbour discovery, the database, path calculation and the routing table.
Follow neighbours and election
Being connected by a cable is only the beginning. Start with Router ID and Hello and Dead timers. Then trace the neighbour states and database exchange, followed by DR/BDR election and failure on a shared LAN. Notice which routers should reach Full and which can correctly remain at 2-Way.
Configure, then prove the result
Use the single-area OSPFv2 lesson to build a working IPv4 example. Check the interfaces, neighbours and destination routes before testing traffic. Once that sequence is familiar, configure OSPFv3 for IPv6 and compare its addressing and verification.
Explain a route or a missing neighbour
Change interface costs and reference bandwidth to predict the preferred path. Compare network types when discovery or election behaves differently. The same module covers passive LANs, default routes and LSA types, so you can connect a setting to its effect.
Build it, break it and recover
Start the three-router lab, then tackle the troubleshooting tickets. Write down a diagnosis before revealing the repair. Use the reference sheet when revising and the course test to check your reasoning.
Extend into area design and security
Once the basic lab works, study areas and ABRs, then compare stub and NSSA designs. Continue with authentication and external routes. These lessons build on the earlier examples; choose them when you can already explain a neighbour table and a single-area route.
Protocol reference
The OSPFv2 protocol behaviour is defined in RFC 2328. Use the vendor references in each configuration lesson to check commands and platform assumptions.