What mechanism does IS-IS use for neighbor relationship establishment reliability?

The three-way handshake is fundamental for establishing reliable neighbor relationships in the IS-IS (Intermediate System to Intermediate System) protocol. This mechanism involves three steps: the sending of a Hello message, the response from the neighbor confirming the receipt, and finally, an acknowledgment that solidifies the relationship as being mutually recognized.

This process ensures that both ends of the link agree on the existence and status of the connection before proceeding to exchange routing information. It enhances reliability by verifying that both routers are not only able to communicate but also that they recognize and accept each other as valid neighbors within the network.

In contrast, other mechanisms like status synchronization, checksum verification, and aging timers serve different purposes in managing and maintaining the integrity and currency of routing information or device states but do not specifically focus on the establishment of neighbor relationships as effectively as the three-way handshake does.