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Configuring the OSPF Protocol
Chapter 360
Configuring the OSPF Protocol
Open Shortest Path First (OSPF) is a link-state routing protocol that
distributes routing information between routers in a single autonomous
system (AS). Each OSPF router transmits a packet with a description of
its local links to all other OSPF routers. The distributed database is built
from the collected descriptions. Using the database information, each
router constructs its own routing table of shortest paths from itself to
each destination in the AS.
OSPF allows you to organize routers, networks, and subnetworks within
an AS into subsets called areas. An area is a grouping of logically
contiguous networks and hosts. Instead of maintaining a topological
database of the entire AS, routers in an area maintain the topology for
only the area in which they reside. Therefore, all routers belonging to an
area must be consistent in their configuration of the area. The topology of
an area is hidden from systems that are not part of the area. The
creation of separate areas can help minimize overall routing traffic in the
AS. Figure 3-3 shows an example of three separate areas defined for an
AS.