In a LISP architecture, which device receives map-requests and determines the appropriate ETR for the requested mapping?

The map resolver (MR) is a core LISP component that receives map-requests from an Ingress Tunnel Router (ITR). Its primary function is to look up the requested Endpoint Identifier (EID) to Routing Locator (RLOC) mapping in the LISP mapping system and then forward the map-reply from the appropriate Egress Tunnel Router (ETR) back to the requesting ITR. A proxy ETR (pETR) is a device that acts as an ETR for LISP sites that do not have their own ETR, but it doesn't resolve mappings. A routing locator (RLOC) is simply the IP address of an ETR, not a device itself. A map server (MS) stores EID-to-RLOC mappings and receives registrations from ETRs, but it doesn't directly resolve map-requests; it works in conjunction with the map resolver to provide the mapping information.