Hello Protocol State Changes

The following is a brief description of the possible OSPF neighbor state changes when the Hello protocol is being used:

• Down—This is the initial state of a neighbor conversation. This state means that no information has been sent from any neighbors. This state is usually seen when a router first begins speaking OSPF in a network or when there is a problem and the router dead interval timer (Hello interval * 4) has expired for some reason, resulting in OSPF.

• Attempt—This is valid only for neighbors that are attached to NBMA networks and reflects that the router has sent Hello packets to the neighbor but has not yet received a response; therefore, the router is attempting to form a neighbor relationship.

• Init—A Hello packet has been seen from the neighbor, but in that Hello packet, the receiving router's ID was not present. Therefore, communication is initialized; however; bidirectional communication has not yet been established with the neighbor.

134 Chapter 3: OSPF Communication

• 2-Way—In 2-way, the routers see their own ID in the neighbor's Hello packet. Communication between the two routers is bidirectional. At this point, the routers decide whether to proceed and become adjacent. If they choose to, they proceed.

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