About this interactive
The OSPF neighbor state machine is usually met as six words in a row — Init, 2-Way, ExStart, Exchange, Loading, Full — and a student who can recite that list still cannot say what has to be true before any one of those transitions can happen, or which of them actually moves routing information. Closing that gap is what this set is for, and it is why no card opens with its state name. Each card describes the mechanism and ends with the state the neighbor table records, so the vocabulary is attached to the behaviour rather than standing in for it. The chronology here is real rather than conventional. Every step is blocked by something the previous one produces, and the two constraints that do most of the work are worth stating plainly because they are what the cards are written to expose. The first is that nothing about the topology crosses the link until the two routers have settled who is leading the conversation: the Database Description packets of ExStart are deliberately empty, and they exist only to elect a master and fix the starting sequence number, without which neither router could later tell a retransmission from a new packet. The second is that a router cannot ask for something it does not know exists. Exchange sends an index — the headers of every link-state advertisement each router holds, not the advertisements themselves — and that index is precisely what lets each side work out what it is missing. Loading is then the request for those specific entries, and it is the only step in the entire adjacency where real topology data actually moves. A student who sees that will never again put Loading before Exchange, because the ordering stops being a convention to memorise and becomes a dependency. The two-way check at 2-Way is the other place the reasoning bites. Hearing a Hello proves only that a neighbor is audible; finding your own Router ID inside the Hello coming back is what proves the link works in both directions, and that is a different claim. It is also the moment the DR and BDR election happens on a multi-access segment, which is why this set carries the priority and Router ID terms even though neither appears as a card of its own. The last two cards deliberately leave the state machine behind, and this is the judgment the set makes about the module it sits in. snc3-06's own lesson, OSPF Process, does not teach the six neighbor states at all — it teaches a five-step arc: hello packets establish neighbors, link-state advertisements are exchanged, the link-state database is built, Dijkstra's algorithm produces the shortest path first tree, and the best route is installed on the routing table. Ending this activity at FULL would have built something technically correct that floats free of the lesson the student just watched. Ending it at the routing table nests the ticket's six states inside the module's own arc, and it forces the distinction the lesson makes explicitly and that students routinely lose: every router in the area holds an identical link-state database, but each runs the SPF calculation from its own position and therefore reaches its own conclusions, and only the routing table ever moves a packet. All eight cards are presented on every run rather than sampled. This is the naturally finite domain the pool guideline makes an exception for: an adjacency with a step removed is not a shorter version of the same object, it is a broken dependency chain, and the chain is the entire skill being assessed. Padding it would mean inventing states OSPF does not have. This pairs best with the module's configuration demos — run it after OSPF Process and before DEMO: Configuring OSPF, so that when show ip ospf neighbor prints FULL/DR in a live capture, the student already knows what had to happen for that word to appear.
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