This application discloses a packet sending method, apparatus, and system, and a storage medium, and relates to the communication field. The method includes: A first device receives a first packet, where the first packet includes a first address prefix, the first device is a border device in a first AS domain, the first address prefix is obtained based on an address prefix advertised by a second device, the second device is located in a second AS domain, the first AS domain is different from the second AS domain, and the first address prefix is used to send a packet to the second device. The first device obtains a second address prefix and identification information of a target flexible algorithm based on the first address prefix, where the second address prefix is used to send a packet to the second device.