Some of the considerations in choosing the OSPF topology depend on its method of updating the network and its effect on network overhead. These considerations are mentioned in RFC 1586, which suggests that the different virtual circuits have different functions:
• A point-to-point circuit—Although no DR or BDR is required, each circuit will have an adjacency, which will create many more adjacencies on the network and will increase the need for network resources.
• An NBMA environment—This may require a DR and a BDR, unless the underlying technology is viewed as point-to point. This is economical for most routers, requiring only two adjacencies, except for the DR and BDR. However, it may require more administration in terms of configuration.
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