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9tut reddit ccna.170 Chapter 8 Implementing the IPv4 OSPF Model The IPv4 OSPF model looks similar to the conceptual diagram in Figure 8-10. Note that the diagram shows that each router has a distinct RID value. Each router has a pointer representing each of its interfaces, and because the LSAs identify neighbors, the SPF can figure out which interfaces are connected to which other routers. The network LSA completes the intra-area topology The router LSA defines most of the intra-area topology, and the network LSA defines the rest. It turns out that when OSPF elects a DR on a subnet, and this DR has at least one neighbor, OSPF treats that subnet as another node in its mathematical network model. To represent this network, the DR creates and floods a network (type 2) LSAO for that network (subnet)For example, going back to Figure 8-9, there is an Ethernet LAN and an Ethernet WAN. the Ethernet LAN between R2 and R3 will elect a DR, and these two routers will become neighbors. Therefore, whichever router is the DR, it will create a network LSA. similarly, Rl and R4 are connected to an Ethernet WAN, so the DR on that link will create a network LSA.Figure 8-11 shows the in-region LSA for the completed version of this design in region 0. Note that when a network LSA exists, the router LSA actually points to the network LSA, which allows the SPF process to connect the parts together.Figure 8-11 Type 1 and type 2 LSAs in region 0, assuming a single region design is usedHint: The first two figures work a bit like a jigsaw puzzle. The SPF algorithm basically solves the jigsaw puzzle, but the way to do that is to look at all the numbers inside the different LSAs and see which LSAs fit next to the other LSAs.Finally, note that in this single-region design example, there are no aggregated (type 3) LSAs at all. these LSAs represent subnets in other regions, and there are no other regions in the example. The next example shows some aggregated LSAs.5.2 Base Content 171LSAs in a multi-region design Migrating from a single-region design to a multi-region design has several effects on LSAs.Each region has fewer router LSAs and network LSAs.ABRs have one copy of the LSDB for each region to which they are connected.