Down to Init State

When OSPFv2 is enabled on the interface, R1 transitions from Down to Init and starts
sending OSPFv2 Hellos out of the interface in an attempt to discover neighbors.

Init State

When a R2 receives a hello from the previously unknown router R1, it adds R1’s router ID
to the neighbor list and responds with a Hello packet containing its own router ID.

Two-Way State

R1 receives R2’s hello and notices that the message contains the R1 router ID in the list of R2’s neighbors.
R1 adds R2’s router ID to the neighbor list and transitions to the Two-Way State.
If R1 and R2 are connected with a point-to-point link, they transition to ExStart
If R1 and R2 are connected over a common Ethernet network, the DR/BDR election occurs.

Elect the DR & BDR

The DR and BDR election occurs, where the router with the highest router ID or highest priority
is elected as the DR, and second highest is the BDR

Synchronizing OSPF Databases

• Decide first router: The router with the highest router ID sends its DBD first.
• Exchange DBDs: As many as needed to convey the database. The other router must acknowledge each DBD with an LSAck packet.
• Send an LSR: Each router compares the DBD information with the local LSDB. If the DBD has more current link information, the router transitions to the loading state.

After all LSRs have been exchanged and satisfied, the routers are considered synchronized and in a full state. Updates (LSUs) are sent:

• When a change is perceived (incremental updates)
• Every 30 minutes