Router Exchange Protocol States in OSPF

B

The correct answer is A. exstart state > loading state > exchange state > full state.

Explanation:

When a router undergoes the exchange protocol within OSPF (Open Shortest Path First), it passes through four different states. These states are:

1. exstart state: In this state, the two routers that are trying to establish an adjacency agree on their router IDs and exchange their initial sequence numbers.

2. exchange state: In this state, the routers exchange database description packets (DBDs) that contain information about their LSAs (Link State Advertisements).

3. loading state: In this state, the router that received the DBD packets requests the missing LSAs from the other router and begins receiving them.

4. full state: In this state, the routers have exchanged all of their LSAs and have established a complete OSPF database. They can now forward traffic through their network.

So, the correct order in which a router passes through each state during the OSPF exchange protocol is exstart state > loading state > exchange state > full state, which is option A.