[ipv6-wg] RIPE 80 IPv6 wg session Wilhelms DSL broke, some unanswered questions

>App Developers try to avoid IPv6, I know. We cannot force them to use 
>IPv6. But we have to force them to use libraries that work with IPv6 and 
>IPv4, not some old stuff useing IPv4 only. Then there is golden rule: no 
>IP addresses in code or config files, use names

My experience is that for simple applications, if you avoid hardcoding
addresses then using just address family agnostic library calls
(getnameinfo and getaddrinfo) should result in something that support s
both IPv4 and IPv6. Note that getnameinfo and getaddrinfo can do a lot of
stuff if you pass the right flags.  Obviously in languages other than C
that only works if equivalent functions are available.

However, for logging it is common to log <addr>:<port>. Obviously if
<addr> is an IPv6 address then you get something that is hard to parse
later. IPv6 addresses are logged as [<ipv6-addr>]:<port>.

Typically you want -4 and -6 switches. Though you can work around that in DNS.

Many applications have some kinds of ACLs or interface configuration. Again
parsing <addr>:<port> doesn't work in IPv6.

It gets more tricky when an IPv6 socket can receive both IPv4 and IPv6 
connections or packets. In that case you may end up with IPv4-mapped 
addresses (::ffff:<ipv4-address>). Note that the presentation format has dots.

A bonus from IPv6, you can bind to ::%<interface-name> to specify a specific
interface to use.