Embodiments of this application relate to the data access field, including data access methods systems that enable efficient and effective data access. In one embodiment, a method includes: assigning, by an RDMA control service based on user information and a corresponding connection relationship between a switch and a first instance defined by a user, an address segment to the first instance; building, by the RDMA control service, an access control list based on the address segment assigned to the first instance, where the access control list is used for controlling access between different first instances defined by the user; and sending, by the RDMA control service, the access control list to a switch control service, such that the switch control service configures the access control list for the switch. In one embodiment, access between different instances defined by a same user can be effectively controlled, thereby effectively resolving an issue of access isolation for different users accessing an RDMA network node.