This kind of tunnel uses IPv4 compatible IPv6 addresses for tunnel interfaces. These addresses are taken from /96 address comprised of the first 96 bits containing all zeros and the last 32 bits are derived from the IPv4 address.
These addresses are written as:
0:0:0:0:0:0:A.B.C.D or ::A.B.C.D
This is not a scalable solution and this method of addressing is not supported globally, Cisco recommends using ISATAP tunnels instead when considering this kind of solution..