From: Florian Weimer <fweimer@redhat.com>
To: Phillip Hellewell <sshock@gmail.com>
Cc: libc-help@sourceware.org
Subject: Re: RFC 6724
Date: Mon, 12 Nov 2018 17:43:00 -0000 [thread overview]
Message-ID: <87ftw6nqcv.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <CA+dWQFppeQKhKJqCj=PqaPD+=tDwNexHVPVeGXo+Um6wRYNoQg@mail.gmail.com> (Phillip Hellewell's message of "Mon, 12 Nov 2018 09:50:27 -0700")
* Phillip Hellewell:
> On Mon, Nov 12, 2018 at 4:20 AM Florian Weimer <fweimer@redhat.com> wrote:
>>
>> RFC 3484 has always been rather problematic (particularly Rule 9, which
>> we do not implement).
>>
>> I seriously doubt that there is any benefit from address sorting. It's
>> a layering violation, and it makes renumbering harder because you now
>> need to consider the impact on address sorting. Its core assumptions
>> are also quite wrong on many networks (e.g., private addresses often
>> have less georeplication than public Internet service, so public
>> addresses are closer by).
>>
>> In any case, I think address sorting should be performed by the caching
>> DNS resolver, not the stub resolver.
>
> An administrator of a given machine may not have any control over the
> DNS server, yet they should still be able to control address order,
> e..g., to prefer IPv4 over IPv6 or vice-versa.
If you can edit /etc/gai.conf, you can install Unbound or dnsmasq, too.
>> Do you have a setup that actually relies on address sorting? Do you
>> have any examples where DNS provides a set of addresses for a single
>> name with different labels/precedence, so that sorting the addresses
>> actually has an effect?
>
> Yes, this happens all the time. Look no further than google.com. It
> has both A and AAAA. As a system administrator, I should be able to
> set up my prefix policy table to prefer IPv4 over IPv6 if desired.
> That is just one example.
Do you have another example that does not involve sorting merely by
protocol? Something that you have encountered personally?
> One should be able to control address order without having to set up
> and run their own special DNS server/proxy/whatever.
To be honest, I don't see any other way to get full RFC 6724 support
because the RFC requires various things for which I do not see direct
kernel support.
If we disable or limit sorting in glibc, at least you will be able to
get RFC 6724 support with a suitable NSS service module or caching DNS
server.
Thanks,
Florian
next prev parent reply other threads:[~2018-11-12 17:43 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-11 20:45 Phillip Hellewell
2018-11-11 21:09 ` Phillip Hellewell
2018-11-12 11:21 ` Florian Weimer
2018-11-12 16:50 ` Phillip Hellewell
2018-11-12 17:43 ` Florian Weimer [this message]
2018-11-13 4:50 ` Phillip Hellewell
2018-11-13 10:51 ` Florian Weimer
2018-11-13 16:49 ` Phillip Hellewell
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