A method and apparatus for implementing multicast. When a multicast source performs route advertisement, route update is performed on a cross-DC integrated device, and a received device identifier and a received AS number are replaced with a device identifier and an AS number that are of the integrated device. In this way, when a multicast user joins the multicast source, each network device in the network can trace the multicast source based on a received route, and determine a multicast path that is from the multicast source to the multicast user. Therefore, it is possible to accurately perform, in a NG MVPN, cross-DC multicast on traffic of the multicast source.