Internet Topology Discovery Using mrinfo

The Internet Group Management Protocol (IGMP - RFC1112) was initially designed to allow hosts to report their active multicast groups to the multicast router on their LAN. However, IGMP also provides some management tools such as the messages used by mrinfo. In practice, an mrinfo reply provides similar information as a show command on the router's command line interface. Therefore, mrinfo allows us to silently collect useful topological information.