Figure 10-37 ABR Route Summarization
Figure 10-38 Discontinuous Network Segment
Link State Database
When the routers in the network completely synchronize the link state database through LSA
exchanges, they can calculate the shortest path tree by basing themselves as the root node.
The OSPF protocol routing calculation is simply presented as below.
1)
Each OSPF router would generate LSA according to its own link state or routing
information, and then send it through the update packets to the other OSPF routers in the
network. LSA is to describe the network topology and the routing information. For instance,
Router-LSA describes the link state of routers; Summary-LSA describes the inter-area
route; and so on.
2)
Each OSPF router collects LSA advertised by the other routers to form an LSDB. All the
Router-LSA and Network-LSA in the LSDB describe the entire intra-area network topology,
while the other types of LSA describe the route to a certain destination in other areas or
external AS.
3)
When all the routers in the network completely synchronize their LSDB, each OSPF router
will calculate a loop-free topology by SPF algorithm to describe the shortest path to every
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