Hello PDU

Hello PDU
Hello PDUs, as we’ve previously discussed, are used to initialize and maintain router adjacencies.
There are actually three types of Hello PDUs:
Level 1 LAN IS-IS Hello PDU The Level 1 LAN IS-IS Hello PDU is used by Level 1 routers to
form adjacencies on broadcast multi-access networks. These PDUs are passed only between
Level 1 routers and L1/L2 routers to form Level 1 adjacencies.
Level 2 LAN IS-IS Hello PDU As you can probably guess from the name, the Level 2 LAN
IS-IS Hello PDUs are used to form Level 2 adjacencies on broadcast multi-access networks.
Level 2 and L1/L2 routers use these PDUs to form Level 2 adjacencies.
Point-to-Point IS-IS Hello PDU The point-to-point IS-IS Hello PDU is used on point-to-point
connections to form adjacencies. The point-to-point IS-IS Hello PDU can be used to form a
Level 1 or Level 2 adjacency.
If you remember from our earlier discussion, an L1/L2 router could use a combination of
these Hello PDUs to form its Level 1 and Level 2 adjacencies