How you represent the address is arbitrary, using a colon instead of a dot matters little as underneath it's just an integer with the only difference being 32 o

How you represent the address is arbitrary, using a colon instead of a dot matters little as underneath it's just an integer with the only difference being 32 or 128bit. Using a dot causes its own problems, because it conflicts with DNS. DNS allows fully numeric domain names, but they conflict with legacy ip so are not used on a the public DNS. Using hex would make the problem worse as it's perfectly valid to have an ipv6 address ending "de" for example, which is the TLD for germany. Legacy addresses can be represented via hex too - try ping 0xdeadbeef. The socket apis between v6 and legacy ip are largely as compatible as they can be, you need to use sockaddr_in6 and AF_INET6 which is the same as you propose. You can open an AF_INET6 socket and still connect to legacy addresses with it. For higher level languages that don't deal with fixed size memory structures directly it's pretty much fully compatible, you can just say "connect www.google.com tcp/443" or equivalent, and the system takes care of resolving what protocol and address to connect to.