To extend LDP across multiple areas of an IGP instance or across multiple IGP instances, the current standard LDP implementation based on RFC 3036 requires that all the /32 prefixes of PEs be leaked between the areas or instances. This is because an exact match of the prefix in the routing table has to install the prefix binding in the LDP Forwarding Information Base (FIB).
Multi-area and multi-instance extensions to LDP provide an optional behavior by which LDP installs a prefix binding in the LDP FIB by simply performing a longest prefix match with an aggregate prefix in the routing table (RIB). The ABR is configured to summarize the /32 prefixes of PE routers. This method is compliant to RFC 5283- LDP Extension for Inter-Area Label Switched Paths (LSPs).