IPv6 scoped addresses

IPv6 introduced scoped addresses:
link-local, site-local, scoped multicast addresses.

Explicit scope designation is necessary.
Advanced API
sin6_scope_id: very limited support, ambiguous spec.

If you need to support link-local, use advanced API.
Do not generate sockaddr by yourself.
getpeername, getsockname, getaddrinfo
Scope boundary routers need a hack.
very few implementations, less experience

Text representation
we propose "<scoped_address>%<scope zone ID>"
e.g. fe80::1234%2 for fe80::1234 on the link "2".
getaddrinfo() will interpret this and set sin6_scope_id accordingly.