If you are on an IPv6 network, you can access to an IPv4 address. We just have to use the 2002: prefix.
for exemple 184.108.40.206 can be converted to hexadecimal : 9D36:1. So we can contact it via 2002:9D36:1::
ISATAP (Intra-Site Automatic Tunnel Addressing Protocol)
If you are on an IPv4 network, you can be contacted via an IPv6 address:
[64bits prefix]:0:5EFE: and the 32bits of the IPv4 address
For exemple : FE80::5EFE:192.168.41.30
If you cannot use 6to4 because of NAT you may use Teredo.
Teredo Prefix is: 2001:0000::/32.