To ensure reliability, typical implementations of the flooding algorithm send new information via all interfaces other than the one the new piece of information was received on. This redundancy is necessary to guarantee that flooding is performed reliably, but implies considerable overhead of utilized bandwidth and CPU time if neighboring routers are connected with more than one link. This document describes a method that reduces this overhead. It may sometime be necessary for OSPF routers to resynchronize their LSDBs. OSPF standard, however, does not allow routers to do so without actually changing the topology view of the network.
Routers find new and detect unreachable neighbors via Hello subprotocol.
Hello OSPF packets are also used to ensure two-way connectivity within time. When a router restarts its OSPF software, it may not know its neighbors. If such a router sends a hello packet on an interface, its neighbors are going to reset the adjacency, which may not be desirable in certain conditions. This memo provides a mechanism that allows OSPF routers to inform their neighbors about the restart process. Note that this mechanism requires support from neighboring routers.