In this paper we deal with the design issues that need to be considered when creating a mobility protocol for MPLS. We explain what decisions need to made when the connection-oriented static MPLS architecture is to be combined with the connectionless and dynamic mobile IP protocol. In addition to the outlining of the design considerations, we describe a protocol that is based on the interworking of MPLS with Hierarchical Mobile IPv6 (HMIPv6) in an "overlay" fashion. The combined protocol is explained with the use of detailed signaling diagrams.