IPv4 only mirrors are still loaded via metalink when ip_resolve=6

[paulcdejean]

$ dnf --version
dnf5 version 5.2.17.0
dnf5 plugin API version 2.0
libdnf5 version 5.2.17.0
libdnf5 plugin API version 2.2

I have an ipv6 only machine. I have this config for /etc/dnf/dnf.conf

[main]
ip_resolve=6

My fedora repository is using metalink:

[fedora]
name=Fedora $releasever - $basearch
#baseurl=http://download.example/pub/fedora/linux/releases/$releasever/Everything/$basearch/os/
metalink=https://mirrors.fedoraproject.org/metalink?repo=fedora-$releasever&arch=$basearch
enabled=1
countme=1
metadata_expire=7d
repo_gpgcheck=0
type=rpm
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-fedora-$releasever-$basearch
skip_if_unavailable=False

However I'm still getting dnf try and pull ipv4 only mirrors...

 Fedora 43 openh264 (From Cisco) - aarch64                                                                                                                               100% |   3.9 KiB/s |  10.3 KiB |  00m03s
 Fedora 43 - aarch64                                                                                                                                                     100% |  14.8 MiB/s |  55.1 MiB |  00m04s
>>> Curl error (6): Could not resolve hostname for http://mirror.cs.princeton.edu/pub/mirrors/fedora/linux/releases/43/Everything/aarch64/os/repodata/repomd.xml [Could not resolve host: mirror.cs.princeton.edu
>>> Curl error (6): Could not resolve hostname for http://mirror.uoregon.edu/fedora/linux/releases/43/Everything/aarch64/os/repodata/repomd.xml [Could not resolve host: mirror.uoregon.edu] - http://mirror.uore
>>> Curl error (6): Could not resolve hostname for http://mirror.cs.princeton.edu/pub/mirrors/fedora/linux/releases/43/Everything/aarch64/os/repodata/5717f03894a6e3eafb8fb078c8d183e3b703de7a5f375f66333d0594f15
>>> Curl error (6): Could not resolve hostname for http://mirror.cs.princeton.edu/pub/mirrors/fedora/linux/releases/43/Everything/aarch64/os/repodata/99c57cbe3029af9f7665c7acb36829177c5e4f2472dbdbaeaa5e2204d0c
>>> Curl error (6): Could not resolve hostname for http://mirror.uoregon.edu/fedora/linux/releases/43/Everything/aarch64/os/repodata/5717f03894a6e3eafb8fb078c8d183e3b703de7a5f375f66333d0594f150e9e3-filelists.x
>>> Curl error (6): Could not resolve hostname for http://mirror.uoregon.edu/fedora/linux/releases/43/Everything/aarch64/os/repodata/99c57cbe3029af9f7665c7acb36829177c5e4f2472dbdbaeaa5e2204d0c06ed2-comps-Every
 Fedora 43 - aarch64 - Updates

mirror.uoregon.edu and mirror.cs.princeton.edu are both domains that exclusively have A records, and don't have AAAA records.

[ppisar]

I see. That's obnoxious. The cause is that DNF5 does not know what domain has which DNS record and thus cannot skip domains without appropriate record or at least suppress the messages for them.

DNF5 delegates operations to librepo which uses libcurl. The messages you see come from libcurl. libcurl reports them because it handles each mirror as a separate URL and the last error of each of them as fatal. librepo then reports each of the libcurl failure and tries one mirror after another.

Here librepo would need to buffer the error messages and report the errors only after exhausting all the mirrors. But someone could object that he want to see the errors immediately (as is done now) instead of waiting to the very end of the mirror list.

I'm curious what other DNF5 developers think about this. I worry this issue is more about how much verbose the download should be.

Another problem is that libcurl does not distinguish between the-domain-does-not-have-required-record and some-other-DNS-error. Users definitively want to see the other DNS errors. That could be worked around by resolving the domains manually in librepo before passing them to libcurl. But that would wasted the DNS resolution, unless librepo would fill librepo's DNS cache manually (is it possible?).

Completely different approach would be enhancing the mirrors list returned from a mirror manager with deails about expected network family support. But that would require changes in Fedora infrastructure.

[paulcdejean]

Released issue: fedora-infra/mirrormanager2#306

[ppisar]

DNF5 developers discussed this topic and nobody was able to propose a good solution.

It was pointed that mirrors become unusable for other reasons than A/AAAA DNS records and that librepo needs more capable mirror selector (with respect to network latency, bandwith, country (#1483), network family). Compare to https://man.archlinux.org/man/extra/reflector/reflector.1.en. So this issue will be probably addressed when librepo gets these capabilities. A part of those capabilities should be remembering the last optimal mirror between DNF5 invocation.