Specification unclarity/incompatibility

Port number space
What is the relationship of port number space between TCP over v4 versus TCP over v6?
Does bind(2) ordering matter?
Solution: Take the safest side, do not assume kernel behavior
getaddrinfo(AI_PASSIVE)
bind(2) to all addresses returned
Die only if all bind(2) fails

IPv6 wildcard bind...
may receive IPv4 traffic as IPv4 mapped addr (RFC2553)
Leads to mistakes/vulnerabilities, low portability, don't use it
Use setsockopt(IPV6_V6ONLY, 1) to avoid mistake
IPV6_V6ONLY is just recently introduced, so platforms may not support this