OSPF (OPEN SHORTEST PATH FIRST)


•OSPF is a Link State Routing Protocol define in (RFC 1131/1247/1583). OSPF version 2 is in RFC 2328, 1998.
•Is a interior gateway protocol (IGP)
•It builds a complete topology map of the network.
•Use Dijkstra’s algorithm to complete the shortest path to each network, thus requires more CPU power to determine route.
•Maintains a Topological Database to a destination which allows OSPF routers to find an alternative route much faster than a RIP router (faster convergence).
•Design for large, scalable internetworks


ADVANTAGES OF OSPF

•OSPF is not dependent upon hop count for choosing the optimal path.
•Highlights of OSPF standard
–Speed of convergence
–Support Variable length subnet masks.
–OSPF updates procedures (better bandwidth utilization)
–Multi-path selection
–Least cost routing
–Routing authentication
–Area routing (support scalable network)

OSPF TERMINOLOGY

•Neighbour
–Referes to a connected (adjacent) router that is running an OSPF process with the adjacent interface assigned to the same area.
•Adjacency
–Refers to the logical connection between a router and its corresponding designated routers and backup designated routers
•Link
–Refers to a network or router interface assigned to any given network.
•Interface
–Is the physical interface on the router
•Designated router (DR)
–Is used only when OSPF router is connected to a broadcast (multi-access) network
•Backup Designated router (BDR)
–Is a hot standby for the Designated Router on broadcast (multi-access) network.
•OSPF Area
–Areas used to establish a hierarchical network.

NETWORK TYPE

Three types of OSPF networks :
Broadcast Networks - network with more than two routers to share a
common network.

Non-Broadcast - network with more than two routers connected Networks to the same network but does not offer broadcast /multicast functionality.

E.g. frame relay.

Point-to-Point - network that connects a single pair of routers.
Network E.g. leased line.