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cisco braindumps.Keep in mind how the router obtains the router ID for OSPF: the maximum IP address of the active loopback interface or the maximum IP address of the active physical interface.1922 Discovering NeighborsOSPF routers learn about OSPF neighbors and create adjacency and topology tables through shared link state announcements (LSAs), of which there are many different types. To learn about connected neighbors and to monitor known neighbors, the OSPF router sends an LSA Hello message every 10 seconds. After discovering a neighbor and establishing an adjacency relationship with it, the router will expect to receive a Hello message from the neighbor; if no Hello message is received from the neighbor within the failure interval (default 40 seconds), the neighbor is declared failed. In this case, the router will announce this information to the other neighboring OSPF routers via LSA messages.RIP accepts routing updates from almost any other RIP router (unless it is using RIPv2 with authentication configured), and OSPF sets some rules about whether and how routing information is shared. First, routing information advertised by another OSPF router is accepted only when an adjacency relationship has been established with it. When this adjacency is established, the two routers become neighbors, indicating that a special relationship exists between them. For two routers to be neighbors, they must be identical in the following ways.. Area number.. Hello timers and expiration timers for the connected interfaces.. OSPF password (if configured) ;. End-of-area flags (end-of-area flags indicate the type of area; end-of-area areas are used to limit the scope of propagation of OSPF messages and routing information and are out of the scope of this book); .. The MTU value of the connected interfaces. If these aspects differ, the two routers will not establish an adjacency relationship and thus ignore routing information advertised by the other.Hello messages are used to discover other OSPF routers and to maintain an adjacency relationship with those routers. To establish an adjacency, two OSPF routers in the same zone must have the same: Hello timer and expiration timer; authentication password (if configured); type (end-section, subend-section, or non-end-section); MTU configured on the connected interfaceo