NMR cancelations cancel previous nonmembership announcements. Following this message is a collection of routing information that can be used by the routers to coordinate the various multicast routing trees in accordance with the RPM algorithm. Metric is used to indicate the metric distance to the route destination. Flags are used for additional control of network routes. Defined flags include an indication that the destination is unreachable and that a split-horizon route is being transferred within the message.
Infinity allows the flexible definition of infinity for the routes being carried by the message.
This is different than RIP, which defaults to infinity being equal to 16. While this provides the advantage of supporting larger networks, care must be taken with large values for infinity. When routing loops are not detected, slow convergence effects can take extremely long periods of time to resolve themselves. Requested destination address provides a list of addresses that the requester is seeking. NMR indicates multicast groups not supported by the advertising router.