Rules of thumb (1)

Do not use in_addr and in6_addr
Use sockaddr, sockaddr_in and sockaddr_in6
(Using u_long for IPv6 is out of question)
in6_addr does not identify peer (no scope information)

Do not use functions that deals with in_addr/in6_addr
gethostbyname gethostbyaddr getipnodebyname getipnodebyaddr
inet_ntop inet_pton inet_aton inet_ntoa