6in4
6in4 is an IPv6 transition mechanism for migrating from Internet Protocol version 4 ( IPv4 ) to IPv6 . 
<triplet> IPv6 transition mechanism <subj> IPv6 <obj> facet of <triplet> Internet Protocol version 4 <subj> IPv6 <obj> followed by <triplet> IPv6 <subj> Internet Protocol version 4 <obj> replaces