CERNET Center/Tsinghua CERNET Center/Tsinghua This document discusses an extension of the algorithmic translation between IPv4 and IPv4-translatable IPv6 addresses. The extended address format contains transport-layer port set identification (PSID) which allows several IPv6 nodes to share a single IPv4 address with each node managing a different range of ports. This address format extension can be used for IPv4/IPv6 translation, as well as IPv4 over IPv6 tunneling.