Re: debian-installer and DHCPv6 / IPv6-only - is this a known problem?

Hi Bastian,

TL;DR: I think it's actually https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1072526

On Sun, Aug 09, 2026 at 08:34:35AM +0200, Bastian Blank wrote:
> On Sun, Aug 09, 2026 at 04:52:11AM +0000, Andy Smith wrote:
> > I'm trying to install Debian 13 on a system that (initially) only has
> > IPv6 connectivity which it has to get from DHCP. There is no SLAAC nor
> > Router Advertisements.
> 
> DHCPv6 is not expected to work without RA. An RA tells systems to use
> DHCPv6, via the M or O flags,

I don't think that is the case. There isn't any MUSTs for RAs in any of
the DHCPv6 RFCs and in RFC 9915 section 18 signalling by flag M or O is
only one of the scenarios in which DHCPv6 might be initiated. The client
deciding to do so is a valid configuration and in fact d-i does do this.

> and provides the router address.

Gateway of course can't come from DHCPv6 but it can come from router
solicitation; d-i does currently do an rdisc6 to get my correct gateway
of fe80::1 before it attempts DHCPv6.

d-i is in fact working with DHCPv6 past the point where the M flag and
gateway would be an issue, which is why I observe this to work up until
host name and domain name questions are answered. Then netcfg kills the
dhcp6c client process with SIGTERM, causing its signal handler to do a
DHCP RELEASE and d-i never asks for a lease again.

Still, we did wonder if it might make a difference so we enabled RAs
with M flag in them. It did not make a difference.

I'll follow up in #1072526 but essentially I can reproduce the same
issue there and the patch or manual workarounds in that bug do resolve
this problem for me, so I'm fairly confident it's that bug.

Thanks,   A
Andy