Open Shortest Path First (OSPF) Adjacency process
OSPF routers exchange several packet types while forming an adjacency and synchronizing the LSDB.
| Packet | Role in adjacency |
|---|---|
| Hello | Discover neighbors, agree on timers and area |
| DBD | Exchange summary of the local LSDB |
| LSR | Request missing LSA details |
| LSU | Deliver requested LSAs |
| LSAck | Acknowledge LSU |
Neighbor state must reach FULL before the LSDB is considered synchronized.
1. OSPF packet
Section titled “1. OSPF packet”
Version: OSPFv2 or OSPFv3
Type:
1- Hello
2- DBD Database Descriptor
3- LSR Link State Request
4- LSU Link State Update (LSA Link State Advertisements are inside LSUs)
5- Link State Acknowledgment
Router ID: Of the advertising router, and interface
Authentication Type:
0 - No password
1 - Plain text password
2 - MD5 authentication
2. Hello packets
Section titled “2. Hello packets”- OSPF discover each other and form adjacencies via Hello packets.
- They send Hello packets out each interface where OSPF is enabled (except passive interfaces)
- Multicast to 224.0.0.5
- Sent every 10 seconds by default