A method for selecting a router node in a LLN (Low power and Lossy Network) type telecommunication network wherein, upon receipt by a router node of a data packet from a host node or an adherence request to a multicast group from a host node, the router node transmits to a root node a MER_Request request of configuration as a multicast router node to serve the host node, and upon receipt of the MER_Request request, the root node determines, from an association table, a configuration of the router node and transmits to the router node a MER_Reply reply message including the determined configuration.