This read-write setting selects the policy for handling multicast traffic that has no matching learned group entry: send it only to query ports (source-only-learning), discard it, or flood it to all ports. An admin chooses discard to prevent an unregistered multicast source from consuming bandwidth on ports that never subscribed to anything. For example, selecting discard(2) stops an unregistered multicast source, such as a misconfigured device suddenly streaming, from flooding its traffic out to every port when no host has actually joined that group.