Cisco Systems Cisco Systems Cisco Systems Since IPv6 connectivity is not yet broadly available, there is a need in NEMO for a simple technology that allows a MIPv6 based Mobile Router to roam over IPv4 networks. The Doors Protocol proposed in this memo allows an arbitrary Mobile Node to roam even within private IPv4 address spaces, across both Network Address Translations (NAT), reverse NAT, and even Port Address Translation (PAT), in order to cope with the reality of today's Internet.