Microsoft IGMPv3 for IPv4 adds the capability for applications to express source filters on multicast group memberships, which allows receiver applications to determine the set of senders (sources) from which to accept multicast traffic. This capability also simplifies support of one-to-many type multicast applications. It is expected that in the future, the same capability will be available in IPv6 as well. This document specifies new socket options and ioctl commands to manage source filters for IP Multicast group memberships. It also defines the socket structures to provide input and output arguments to these new APIs. These extensions are designed to provide access to the source filtering features, while introducing a minimum of change into the system and providing complete compatibility for existing multicast applications.