Alibaba Group Alibaba Group Cisco Systems, Inc. Cisco Systems, Inc. Cisco Systems, Inc. British Telecom On a multi-access network, one of the PIM-SM (PIM Sparse Mode) routers is elected as a Designated Router. One of the responsibilities of the Designated Router is to track local multicast listeners and forward data to these listeners if the group is operating in PIM-SM. This document specifies a modification to the PIM-SM protocol that allows more than one of the PIM-SM routers to take on this responsibility so that the forwarding load can be distributed among multiple routers.