| Packet or PDUs Protocol Data Unit | |
| IS-IS hello (IIH) PDUs | |
| Link-state PDUs | state of adjacencies to neighboring IS-IS systems on PtP links ack by CSNPs |
| Complete sequence number PDUs (CSNPs) | |
| Partial sequence number PDUs (PSNPs) | |
| DIS Election | on Broadcast & multi-access |
router with the higher priority Default priority: 64 Priority = 0 >> ineligible | |
| Highest priority | |
| priority tie >>> highest SNAP or Mac@ | |
| pseudo-node ( Bcst Network = router ) | on Broadcast & multi-access |
| all router adv a single link ( not all the adj ) to the pseudo-node | |