I guess it is https://github.com/openSUSE/mirrorbrain/issues/4 , where mirror cannot do ipv6 (and client cannot do ipv4).

I recommend you try mirrorcache-eu.opensuse.org (assuming that you are in Europe) instead of download.opensuse.org, it should give more priority for those mirrors that support ipv6 if client uses ipv6.
You can check the mirror list e.g. with command:
curl -s https://mirrorcache-eu.opensuse.org/download/repositories/mozilla/openSUSE_Tumbleweed/x86_64/MozillaFirefox-88.0-1.1.x86_64.rpm.metalink

(the command should be retried few minutes later if it doesn't show anything for locations which nobody ever checked),

MirrorCache is a pilot alternative to download.opensuse.org , so it is not official way yet - use it on own risk.
To enable MirrorCache - backup content of /etc/zypp/repos.d and then execute command as root:
sed -i 's,download.opensuse.org,mirrorcache-eu.opensuse.org/download,' /etc/zypp/repos.d/*.repo

Regards,
--
Andrii Nikitin <andrii.nikitin@suse.com>
DevOPS Automation and Build Service Engineer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5
90409 Nuremberg
Germany

(HRB 247165, AG München)
Managing Director: Felix Imendörffer

From: Per Jessen <per@opensuse.org>
Sent: Monday, April 26, 2021 12:05 PM
To: mirror@opensuse.org <mirror@opensuse.org>
Subject: Re: mirror.tspu.ru is not resolvable, but is the only mirror that serves Mozilla repo
 
Nicolas FORMICHELLA wrote:

> Hello,
>
> The default mirror for my region (EU) mirror.tspu.ru, is unresolvable,
> but it still redirect me to the mirror, which fails update because
> this the only mirror that serves the mozilla repo
>
(https://download.opensuse.org/repositories/mozilla/openSUSE_Tumbleweed/x86_64/)

AFAICT,

mirror.tspu.ru resolves just fine.  (

According to the marker, "mirror.tspu.ru" does not carry repositories,
but it seems to do so anyway :-)

when I pick a file from

http://download.opensuse.org/repositories/mozilla/openSUSE_Tumbleweed/x86_64

I get offered 6 EU mirrors, including mirror.tspu.ru.



--
Per Jessen, Zürich (13.2°C)
http://www.hostsuisse.com/ - dedicated server rental in Switzerland.