OVERVIEW OF OSPF
OVERVIEW OF OSPF
OSPF is a link state protocol that distributes routing information between routers belonging to a single IP domain, also known as an autonomous system. In a link state routing protocol, each router maintains a database describing the topology of the autonomous system. Each participating router has an identical database maintained from the perspective of that router.
From the link state database (LSDB), each router constructions a tree of shortest paths, using itself as the root. The shortest path tree provides the route to each destination in the Autonomous System. When several
LINK STATE DATABASE
Upon initialization, each router transmits a link state advertisement (LSA) on each of its interfaces. The LSA contains the following information for each link:
•IP network number of the link
•Subnet mask of the link
•Metric for the link
•Operation status (up or down) of the link
LSAs are collected by each router and entered into the LSDB of each router. OSPF uses flooding to distribute LSAs between routers. Any change in routing information is sent to all of the routers in the network. All routers within an area have the exact same LSDB.
AREAS
OSPF allows parts of a networks to be grouped together into areas. The topology within an area is hidden from the rest of the autonomous system. Hiding this information enables a significant reduction in LSA traffic, and reduces the computations needed to maintain the LSDB. Routing within the area is determined only by the topology of the area.
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