To facilitate the establishment of Label Switched Paths (LSPs) that would span multiple IGP areas in a given Autonomous System (AS)@ this document describes a new optional Longest-Match Label Mapping Procedure for the Label Distribution Protocol (LDP). This procedure allows the use of a label if the Forwarding Equivalence Class (FEC) Element matches an entry in the Routing Information Base (RIB). Matching is defined by an IP longest-match search and does not mandate an exact match.