TP-Link JetStream T2700G-28TQ User Manual page 198

Link State Database
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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
destination in the network as it knows. This loop-free topology is so-called the SPF algorithm
tree.
4) Each router will establish its own routing table according to the SPF algorithm tree.
OSPF Protocol Packet Type
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During the entire learning process, OSPF routing protocol uses five types of packet, all of which
are IP packets. The packets with 89 as its IP header protocol segment are OSPF ones. This
device abides by the standard RFC protocol. And we are going to introduce the packet formats
involved in the course of OSPF routing protocol running according to the definition by RFC
documentation, and attached with the images and the meaning of key segments.
1. OSPF Header
In the course of routing learning, OSPF uses five types of packet, which have the same OSPF
header, as shown below.
Figure 10-38 Discontinuous Network Segment
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