What is the correct sequence of OSPF adjacency formation?
A.
Down, Init, ExStart, 2way, Loading, Exchange, Full
B.
Down, 2way, Init, ExStart, Exchange, Loading, Full
C.
Down, Init, 2way, ExStart, Exchange, Loading, Full
D.
Down, Init, 2way, Loading, ExStart, Exchange, Full
Explanation:
When OSPF adjacency is formed, a router goes through several state changes before it becomes fully adjacent with its neighbor. The states are Down -> Attempt (optional) -> Init -> 2-Way -> Exstart -> Exchange -> Loading -> Full. Short descriptions about these states are listed below:* Down: no information (hellos) has been received from this neighbor.
* Attempt: only valid for manually configured neighbors in an NBMA environment. In Attempt state, the router sends unicast hello packets every poll interval to the neighbor, from which hellos have not been received within the dead interval.
* Init: specifies that the router has received a hello packet from its neighbor, but the receiving routers ID was not included in the hello packet
2-Way: indicates bi-directional communication has been established between two routers.
* Exstart: Once the DR and BDR are elected, the actual process of exchanging link state information can start between the routers and their DR and BDR.
* Exchange: OSPF routers exchange database descriptor (DBD) packets
* Loading: In this state, the actual exchange of link state information occurs
* Full: routers are fully adjacent with each other