TP-Link T3700G-28TQ T3700G-28TQ V1 UG - Page 182
Area and Route Summarization, Area Model
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Figure 10-32 Flooding of the LSA 1) DROthers multicast the LSA update of its directly-connected network to DR and BDR. 2) After receiving the LSA update, DR floods it to all the adjacent routers. 3) After receiving the LSA update from DR, the adjacent routers flood it to the other OSPF interfaces in their own areas. Area and Route Summarization OSPF protocol gets every router in the network to obtain a complete network topology through adjacency relationship, thus to calculate the routing table and accomplish the forwarding of network data. As the network grows in size, every router has to spend plenty of resources to store LSDB and calculate routing table, so any delicate changes in the network topology will require the routers in the entire network to re-synchronize and re-calculate, which will cause the network to be in the state of frequent "oscillation". In order to run effectively and efficiently in a large-scale network, OSPF protocol can divide the routers in an autonomous system into logic areas identified by Area ID. After the area partition, the intra-area routers will accomplish the route addressing and data forwarding according to the standard OSPF routing protocol. While the boundary routers of multiple areas will have to summarize the information from the routers of all areas to the backbone area that is identified as Area 0, and then the backbone area will advertise these summary to the other areas. As below is the model of area partition. Figure 10-33 Area Model As shown above, a large-scale network is divided into three areas: Area 0, Area 1 and Area 2. Area 1 and Area 2 exchange the routing information via Backbone Area, which has to maintain its 171