One embodiment of the present invention provides a system for facilitating layer-2 subnet extension. During operation, the system can query, from a first administrative domain, a remote database of a second administrative domain for configuration information associated with one or more remote network segments. The system can obtain, from a user interface of the first administrative domain, an instruction for performing layer-2 subnet extension from a first network segment under the first administrative domain to a second network segment of the one or more remote network segments for providing a common layer-2 broadcast domain. The system can then send a remote instruction executable in the second administrative domain for configuring a remote endpoint for the extension. The system can also configure a local endpoint in the first network segment for the extension. Subsequently, the system can establish a data connection between the local and remote endpoints for the extension.