Disclosed herein are a method for implementing switching between layer-2 multicast route tracing and layer-3 multicast route tracing, and a method, a system, a router and an apparatus for differentiating between a layer-2 property and a layer-3 property. One of the methods includes: The query apparatus judges whether to perform layer-2 multicast route tracing, and adds an IP option of layer-2 multicast route tracing into the IGMP Tracert Query packet if layer-2 multicast route tracing needs to be performed. The last-hop router receives the IGMP Tracert Query packet, judges whether the packet carries the IP option of layer-2 multicast route tracing, and transmits the IGMP Tracert Query packet to a downstream layer-2 node transparently if the packet carries the IP option, or initiates layer-3 multicast route tracing if the packet carries no such IP option. The method, system, and router disclosed herein can implement switching between layer-2 multicast route tracing and layer-3 multicast route tracing, and enable the query apparatus to identify the layer property of each IGMP Tracert Response data block.