From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 17651 invoked by alias); 12 Nov 2018 17:43:54 -0000 Mailing-List: contact libc-help-help@sourceware.org; run by ezmlm Precedence: bulk List-Subscribe: List-Post: List-Help: , Sender: libc-help-owner@sourceware.org Received: (qmail 17640 invoked by uid 89); 12 Nov 2018 17:43:54 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-1.4 required=5.0 tests=BAYES_00,KAM_NUMSUBJECT,SPF_HELO_PASS autolearn=no version=3.3.2 spammy=proxy, administrator, phillip, networks X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Mon, 12 Nov 2018 17:43:52 +0000 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 9031858E27; Mon, 12 Nov 2018 17:43:51 +0000 (UTC) Received: from oldenburg.str.redhat.com (ovpn-116-54.ams2.redhat.com [10.36.116.54]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D19451019632; Mon, 12 Nov 2018 17:43:50 +0000 (UTC) From: Florian Weimer To: Phillip Hellewell Cc: libc-help@sourceware.org Subject: Re: RFC 6724 References: <87lg5yr17v.fsf@oldenburg.str.redhat.com> Date: Mon, 12 Nov 2018 17:43:00 -0000 In-Reply-To: (Phillip Hellewell's message of "Mon, 12 Nov 2018 09:50:27 -0700") Message-ID: <87ftw6nqcv.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-IsSubscribed: yes X-SW-Source: 2018-11/txt/msg00009.txt.bz2 * Phillip Hellewell: > On Mon, Nov 12, 2018 at 4:20 AM Florian Weimer 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