Re: IPv4 and IPv6 addresses in resolv.conf

[Rob <robpilling@gmail.com>]

Rich Felker, Sat, 30 Nov 2013:
>>
>> It is EAFNOSUPPORT if no kernel support at all.
>>
>> Actually I don't think there can be any cases where sending to the
>> v4-mapped address (ie ::ffff:1.2.3.4) can fail where an ipv4 socket
>> will succeed because those are basically ipv4 sockets with just ipv6
>> notation, those addresses can't be routed by the ipv6 stack. So it
>
> One thing I'm confused about is the addresses on the actual packets.
> If we've already called bind for address :: and gotten assigned port
> N, does this also reserve port N on 0.0.0.0, which will be needed when
> sending from (and receiving back) IPv4 packets? Also, is there some
> kernel option we might need to worry about that prevents :: from
> receiving packets sent to IPv4 addresses, or does that only apply to
> TCP, not UDP?

I've been seeing this output consistently from mpd at startup:

 	listen: bind to '0.0.0.0:6600' failed: Address already in use
 	(continuing anyway, because binding to '[::]:6600' succeeded)

mpd is the only program on my machine that binds to 6600 so it would
appear that :: port bindings reserve the ipv4 port too. Could be a
kernel configuration option though...

Rob