OSPF uses the priority to select a designated router (DR) and a backup DR (BDR).
?– DR and BDR IP addresses: These are the IP addresses of the DR and BDR for the speci?¬?c
network, if they are known.
?– Authentication password: If router authentication is enabled, two routers must exchange the
same password. OSPF has three types of authentication: Null (no authentication), simple
(plain-text passwords), and MD5. Authentication is not required, but if it is enabled, all peer
routers must have the same password.
?– Stub area ?¬‚ag: A stub area is a special area. Designating a stub area is a technique that
reduces routing updates by replacing them with a default route. Two routers must agree on the
stub area ?¬‚ag in the hello packets.
SPF Algorithm
The SPF algorithm places each router at the root of a tree and calculates the shortest path to each
node, using Dijkstra??™s algorithm, based on the cumulative cost that is required to reach that
destination. LSAs are ?¬‚ooded throughout the area using a reliable algorithm, which ensures that
all routers in an area have the same topological database. Each router uses the information in its
topological database to calculate a shortest path tree, with itself as the root.
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