My prediction about covering network types was wrong. I’m going to puke out some information about neighbor states for now. As is always the case, corrections are welcome.
Down : No hellos have been received from this router.
Attempt : This state only applies to manually-configured neighbors on an NBMA network. In this state, a router has sent unicast hellos to the neighbor but has not received any back from it.
Init : The router has received hellos, but none of the hellos have the router’s RID included as a known neighbor.
2way : The router has received hellos with its RID included. This means the other router has received the hellos from this router, so they now have 2-way communication going. The DR and BRD is elected at the end of this stage.
ExStart: When a router grows up and starts to have feelings for other routers, it enters the ExStart state to have further relations with a neighbor. This is where the master/slave relationship and the initial sequence numbers are established.
Exchange : Once we know who wears the pants in this relationship, the master sends over a DBD with it’s LSAs listed. In response, the slave does the same so that both routers have all the LSA headers they both know.
Loading : This is where the LSRs and LSUs flow. If a router need the full LSA from the neighbor, it sends an LSR, and the neighbor should send an LSU in response.
Full : After the LSR/LSU exchange, the routers should both be in sync, so they each send an LSAck to the other to confirm.
As a bonus, here’s a nifty little animation showing neighbor states.
https://masto.ai/@aconaway
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