During operation, a layer-3 (L3) router can receive a trace query to trace multicast paths associated with a multicast group. In response to detecting a layer-2 (L2) switch coupled to the L3 router, the L3 router can construct a request packet and send the request packet to the coupled L2 switch. The request packet comprises a first data block indicating that the request packet is an L2 multicast trace request, thereby causing the L2 switch to propagate the request packet to downstream L2 switches until the request packet reaches a last-hop L2 switch. The L3 router can receive, from the last-hop L2 switch, a reply packet responsive to the L2 multicast trace request, the reply packet comprising one or more data blocks, with each data block comprising information about an L2 switch or client device present on a traversed multicast path for the multicast group.