Embodiments of this application disclose a communications method, apparatus, and system. Specifically, after receiving information about a multicast area from a sender of a multicast service, a first core network device in a first network obtains, based on the information, indication information indicates that the first network cannot support the multicast service in the multicast area, or indicates that the first network supports the multicast service in a portion of areas of the multicast area; and sends the indication information to the sender. In this way, the sender of the multicast service can determine whether the first network supports the multicast service in the multicast area.