Hi Patrick, On 2021-May-14 23:40:04 +0200, "Patrick M. Hausen" <hau...@punkt.de> wrote: >do you have some spare time and would you be so kind to look at our discussion >here: https://github.com/AdguardTeam/AdGuardHome/issues/3015 > >Andrey from the AdGuard team references this golang issue: >https://github.com/golang/go/issues/8329 > >Which references this FreeBSD issue: >https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=193246
I've skimmed through all three issues. >What I as a sysadmin can observe is that the test code Andrey gave me >binds to *.53 on IPv4 and IPv6 although I start it with `-l 0.0.0.0` which is >clearly an IPv4 "any" address. > >I am not 100% familiar with the API but as I understand you can treat >IPv4 as IPv6 via the socket interface by using an IPv4-mapped IPv6 >address. So far so good. Yes. >But then of course you have an AF_INET6 socket and it seems that >FreeBSD does not allow setting IPv4 specific options via setsockopt() >because it's an IPv6 socket. Correct? That's my reading of the FreeBSD issue. >Why can you have a single socket on both address families, anyway? >IPv4 and IPv6 are as "related" as IP and IPX - if you go dual stack, >treat them both separately - no? This is getting outside my expertise but my understanding is that the idea behind using IPv4-mapped addressed is to simplify building dual-stack applications, particularly during the early introduction of IPv6. The main benefit is that it made it possible to support both IPv4 and IPv6 without needing 2 sockets - which means you can stick to doing an accept() on a blocking socket, rather than needing to use poll() or select() etc with a pair of non-blocking sockets. I'm not sure how to solve your problem, sorry. -- Peter Jeremy
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