"I have no idea what I'm doing ...", sound familiar? With mcjoin you can verify IPv4 multicast connectivity without having to know what you're doing.
SMCRoute is a daemon and command line tool to manipulate the multicast routing table in the UNIX kernel. Both FreeBSD and Linux kernels are supported, but it may work on other systems as well. SMCRoute can be used as an alternative to dynamic multicast routing daemons like mrouted or pimd in situations where (only) static multicast routes should be maintained and/or no proper IGMP signaling exists.
Stand alone UNIX implementation of RFC4286 Multicast Router Discovery Protocol.
pimd is a lightweight, stand-alone implementation of the Protocol Independent Multicast-Sparse Mode (PIM-SM/SSM) specification.
Tools for multicast testing (msend and mreceive)