Once a new neighbor is discovered, the intermediate systems must exchange their databases. To exchange databases, four special types of packets are used: level 1 and level 2 link state packets, complete sequence number packets (CSNPs), and partial sequence number packets (PSNPs). Each of these packet types is described below.
Level 1 and Level 2 Link State Packets
While ISO 10589 defines separate level 1 and level 2 link state information packet types, they are similar enough in structure that we are going to cover both types together, with just the differences between them noted below. Level 1 link state packets are type 18, and level 2 link state packets are type 20. In addition to the information contained in the common ...