Comment # 5 on bug 1175641 from Dominik Platz

(In reply to Jonathan Kang from comment #4)
> Hi Dominik
> 
> Upstream developers left some feedback there. Do you agree that it's due to
> router misconfiguration?
> 
> It seems that there is nothing left to do at NetworkManager side. But as you
> mentioned in comment#0, modifying the default value of accept_redirects can
> help. If you think this should be changed in Tumbleweed, please modify the
> bug title to reflect the issue. I'll re-assign this bug to someone who is in
> charge of this to take a look.
> 
> Thanks.

I would not say that there is a misconfiguration of the router. The router's
behavior is basically understandable and makes sense (in principle). 
The behavior of NetworManager also makes sense.

Only solution #1 (comment#0) remains as practicable.
=> Enable redirects from router.
"sudo sysctl net.ipv6.conf.enp0s3.accept_redirects=1"

BTW: All the Ubuntu distributions do this (tested with Linux Mint 20
(Cinnamon), Neon (KDE & NetworkManager), Kubuntu 20.04.3) as well as Arch
Linux.