/mcpIntroduction This document describes common problems and solutions for IP multicast. Prerequisites Requirements There are no specific requirements for this document. Components Used This document is not restricted to specific software and hardware versions. The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential impact of any command. Background Information When you troubleshoot multicast routing, the primary concern is the source address. Multicast has a concept of Reverse Path Forwarding (RPF) check. When a multicast packet arrives on an interface, the RPF process checks to ensure that this incoming interface is the outgoing interface used by unicast routing in order to reach the source of the multicast packet. This RPF check process prevents loops. Multicast routing does not forward a packet unless the source of the packet passes a RPF check. Once a packet passes this RPF check, multicast routing forwards the packet based only upon the destination address. Like unicast routing, multicast routing has several available protocols, such as Protocol Independent Multicast dense mode (PIM-DM), PIM sparse mode (PIM-SM), Distance Vector Multicast Routing Protocol (DVMRP), Multicast Border Gateway Protocol (MBGP), and Multicast Source Discovery Protocol (MSDP). The case studies in this document walk you through the process to troubleshoot various problems. You can see which commands are used in order to quickly pinpoint the problem and learn how to resolve it. The case studies listed here are generic across the protocols, except where noted. Router Does Not Forward Multicast Packets to Host Due to RPF Failure This section provides a solution to the common problem of an IP multicast RPF failure. This network diagram is used as an example.