What is an “mrouter”?
An mrouters is a multicast capable router. In today’s Mbone most mrouters are Suns running SunOS 4.1.X with the mroute-daemon (mrouted). New developments however are underway (see appropriate questions below). Mrouters maintain connections, called “tunnels” between each other. Mrouters connecting to an ethernet also have the possibility of broadcasting the multicast packets over the ethernet. An mrouter is only an mrouter if it has at least two tunnels (or one tunnel and an ethernet interface).