Bug#1072526: DHCPv6 still non-functional in trixie installer

Hi,

As noted in
<https://lists.debian.org/msgid-search/[email protected]>
I just wanted to confirm that this problem still exists in the trixie
installer (also tested with the daily installer image).

On an IPv6-only network with no SLAAC, gateway provided by router
solicitation, d-i attempts DHCPv6 which succeeds and networking is
initially functional.

After the host name and domain name questions are answered, netcfg does
still issue a kill -TERM to the dhcp6c process. This causes dhcp6c to
send a DHCP RELEASE packet and de-configure the interface. d-i does not
request a lease again later, so it's not possible to continue the
install.

The environment is a bit unusual in that there's no SLAAC and no router
advertisements; the prefix is /127 (just this host and its gateway).
This is a valid configuration though and it does work fine from an
installed Debian using the "dhcp" method in /etc/network/interfaces.

The patch provided earlier in this bug, at
<https://salsa.debian.org/installer-team/netcfg/-/merge_requests/18>
does avoid the issue by doing kill -KILL.

A workaround is to switch to the installer shell after dhcp6c has been
killed and launch it again:

# dhcp6c -c /var/lib/netcfg/dhcp6c.conf eno1

Or, one can hack in the patch's -KILL behaviour in kill-all-dhcp before
network configuration happens:

# sed -i 's/-TERM/-KILL/' /usr/bin/kill-all-dhcp

Possibly placing a patched /usr/bin/kill-all-dhcp file there could be
done in a preseeded early_cmd if that's easier than deploying the patch.

Without this, DHCPv6 is not feasible; install on an IPv6-only network
can only be carried out when there is SLAAC or static networking
configuration.

Thanks,
Andy