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Init state

As explained in Acing the CCNA Exam: Volume 1 Fundamentals and Protocols

The Init state is an OSPF neighbor state in which a router has received a hello message that does not contain its own router ID.

The Init state means a router has received an OSPF hello message from a neighbor, but the hello does not include the local router's router ID (RID). The receiving router records the neighbor and sends a hello that includes the neighbor's RID. section 18.3.1

R2 detects R1

When R2 first receives R1's hello, R2 records R1 in Init: `show ip ospf neighbor` displays `172.16.1.1 ... INIT/DROTHER`. R1 then learns R2's RID and reaches 2-Way, while R2 reaches 2-Way after receiving R1's next hello containing R2's RID. section 18.3.1

How Acing the CCNA Exam: Volume 1 Fundamentals and Protocols covers it

How deep it goes
Explains the missing-RID condition and hello-based transition to 2-Way, but does not detail later adjacency states.
Examples
Uses an R1/R2 hello exchange and Cisco show ip ospf neighbor output showing INIT/DROTHER and 2WAY/DROTHER.
What it assumes
Assumes basic OSPF hello messages and router IDs while defining the Init condition through an R1/R2 exchange.
What you can do after
Diagnose/debug with show ip ospf neighbor by identifying neighbors stalled in the Init state.
How it connects
Connects OSPF hello messages, router IDs, neighbor states, 2-Way state, and OSPF adjacency.
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