A Location/Identifier Separation Protocol (LISP) mapping server, including: a network interface for communicating with a LISP-enabled network; a mapping database; an extranet policy table; and a shared subnetwork mapping engine (SSME), including at least a hardware platform, configured to: receive a map request from a first endpoint serviced by a first xTR, the first endpoint on a first subnetwork, the map request for a second endpoint; determine that the second endpoint is not a member of the first subnetwork; query the extranet policy table to identify a second subnetwork that the first subnetwork subscribes to, and to determine that the second endpoint is a member of the second subnetwork; and provide to the first subnetwork a routing locator (RLOC) of an xTR servicing the second endpoint.