Internet Society France Telecom Comcast France Telecom Internet Society The completion of IPv4 address allocations from IANA and the RIRs is causing service providers around the world to question how they will continue providing IPv4 connectivity service to their subscribers when there are no longer sufficient IPv4 addresses to allocate them one per subscriber. Several possible solutions to this problem are now emerging based around the idea of shared IPv4 addressing. These solutions give rise to a number of issues and this memo identifies those common to all such address sharing approaches. Solution- specific discussions are out of scope.