Applications that deliver substantially the same content at substantially the same time to multiple destination devices, such as Internet Protocol Television (IPTV), web-conferencing, video conferencing, and other multi-user applications, typically use multicast communication, or “multicasting,” to reduce network bandwidth consumed and ease server burdens. Multicasting network packet data involves using network devices to replicate packets for receipt by multiple recipients and thereby reduce the transmission burden on the sender, leading to scalability and more efficient packet delivery to multiple recipient devices. Because the network replicates multicast packets at these network devices, multicasting may reduce the redundant transmission that may occur when transmitting data for the above multi-user applications.
Collections of interested receivers receiving the same stream of Internet Protocol (IP) packets, usually from the same multicast source, are referred to as multicast groups. Routers in an IP multicast network use a multicast routing protocol to build a multicast distribution tree to deliver multicast traffic, addressed to a group IP address, to the interested receivers. In a router that participates in implementing a multicast distribution tree for a particular multicast group, interfaces that lead toward the sources and receive multicast packets from a parent router of the tree are inbound interfaces. The router internally replicates multicast packets received at inbound interfaces and outputs the replicated multicast packets to one or more outbound interfaces leading toward the receivers.