This application provides a method for implementing a Layer 3 virtual private network (L3VPN) and an apparatus. The method includes receiving, by a first PE, an attachment notification packet sent by a first terminal device, a first site attaches to an L3VPN by using the first PE; a second site attaches to the L3VPN by using a second PE, and a first terminal device attaches to a second site before attaching to the first site. The method also includes obtaining, by the first PE, an IP address of a second terminal device, and the second terminal device attaches to the second Site; and sending, by the first PE, a binding update notification packet to the first terminal device, where the binding update notification packet carries a MAC address of the first PE and the IP address of the second terminal device.