Nokia Siemens Networks This document defines how a membership test can be used to convey all or some of the EID-to-RLOC mappings from an Egress Tunnel Router to requesting Ingress Tunnel Router. This draft proposes that an authoritative ETR MAY return a group membership test in the LISP Map- Reply Message that indicates if a given EID is served by the ETR. The membership test is implemented as a Bloom filter. A Bloom filter is compact data structure to represent a set of elements. The membership test "aggregates" EIDs beyond prefix based aggregation. Membership test decreases the load of the mapping system and distributes the EID-to-RLOC resolution between an ITR and an ETR.