Open Shortest Path First is a link state routing algorithm used in interior gateway routing. Routers maintain a database of all routers in the autonomous system with links between the routers, link costs, and link states (up and down).
Open Shortest Path First (OSPF) is a routing protocol for Internet Protocol (IP) networks. It uses a link state routing (LSR) algorithm and falls into the group of interior gateway protocols (IGPs), operating within a single autonomous system (AS).
| Communication protocol | |
| Purpose | Routing protocol |
|---|---|
| Introduction | 1989 |
| RFC(s) | 1131, 1247, 1583, 2178, 2328, 3101, 5709, 6549, 6845... |
| Communication protocol | |
| Introduction | 1999 |
|---|---|
| RFC(s) | 2740, 5340, 6845, 6860, 7503, 8362... |
OSPF gathers link state information from available routers and constructs a topology map of the network. The topology is presented as a routing table to the Internet Layer for routing packets by their destination IP address. OSPF supports Internet Protocol Version 4 (IPv4) and Internet Protocol Version 6 (IPv6) networks and supports the Classless Inter-Domain Routing (CIDR) addressing model.
OSPF is widely used in large enterprise networks. IS-IS, another LSR-based protocol, is more common in large service provider networks.
Originally designed in the 1980s, OSPF is defined for IPv4 in protocol version 2 by RFC 2328 (1998). The updates for IPv6 are specified as OSPF Version 3 in RFC 5340 (2008). OSPF supports the Classless Inter-Domain Routing (CIDR) addressing model.
