NBMA (non-broadcast multiple access) is one of four network types in the OSPF (Open Shortest Path First) communications protocol. NBMA is used to accurately model X.25 and frame relay environments in multiple-access networks where there are no intrinsic broadcast and multicast capabilities. The other OSPF network types are: broadcast, point-to-point, and point-to-multipoint. In an NBMA configuration, OSPF sends HELLO packets (packets sent periodically to establish and confirm neighbor relationships between routers) to each router one at a time rather than multicasting them. The HELLO timer (which tells the router how often to send HELLO packets) is extended from 10 to 30 seconds and the dead router timer (which tells the router how long to wait before it decides that a neighboring router is not functioning) is extended from 40 to 120 seconds.
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