Open Shortest Path First is a routing protocol for Internet Protocol networks. It uses a link state routing algorithm and falls into the group of interior gateway protocols, operating within a single autonomous system. It is defined as OSPF Version 2 in RFC 2328 for IPv4
| Packet Name | Type/Number | Function |
|---|---|---|
| Hello | 1 | Discovers and maintains neighbors. |
| Database description | 2 | Summarizes database contents. |
| Link state request | 3 | Requests LSAs that need to be downloaded to requesting router. Only sent during Exchange, Loading, or Full state. |
| Link state update | 4 | Contains a list of the LSAs that are to be updated. Often used in flooding, as discussed later in this chapter. |
| Link state acknowledgment | 5 | Acknowledges the packets sent out during flooding to ensure efficient use of floods. |