Neighbor Discovery

When an intermediate system is first attached to a link (or physical interface, either through the booting process, configuration, or bringing the link up), it will begin sending hello packets, which discover and maintain neighbor adjacencies. If it receives hello packets back from any other IS, it will begin building an adjacency with this new neighbor. On point-to-point links, a three-way handshake is used to establish a reliable adjacency between the two end points. This mechanism is an extension to the two-way handshake described in ISO Standard 10589. On broadcast networks, the local MAC (physical layer) address of the IS must be in the hello packets received from other intermediate systems for a neighbor relationship ...

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