Intermediate System to Intermediate System Hello (IIH) packets discover IS-IS neighbors and establish and maintain IS-IS adjacencies. An IIH is sent in every Hello-interval to maintain the established adjacency. If a node has not heard IIHs from its neighbor for (hello-interval x hello-multiple) seconds, the node tears down the adjacency. IIH carries TLV 143 and SPB B-VLAN Sub-TLV (among other sub-TLVs). For two nodes to form an adjacency the B-VLAN pairs for primary B-VLAN and secondary B-VLAN must match.
Link State Packets (LSP) advertise link state information. The system uses the link state information to compute the shortest path. LSP also advertises MT-capability TLV 144 and SPB instance Sub-TLV, and SPB I-SIDs Sub-TLV.
Complete Sequence Number Packets (CSNP) contain the most recent sequence numbers of all LSPs in the database. CSNP notifies neighbors about the local LSDB. After a neighbor receives a CSNP, it compares the LSPs in the CSNP with the LSP in the local LSDB. If the neighbor is missing LSPs, it sends a Partial Sequence Number Packets (PSNP) to request the missing LSPs. This process synchronizes the LSDBs among neighbors. A synchronized LSDB among all nodes in the network is crucial to producing a loop-free shortest path.