Re: systemd-networkd: IPv6 prefix delegation lost when changing prefixes
For anyone stumbling upon this in the future, there is some more
discussion on the systemd-devel mailing list:
https://lists.freedesktop.org/archives/systemd-devel/2020-April/044358.html
and I opened an issue on GitHub:
https://github.com/systemd/systemd/issues/15455
Tobias Brink <tobias.brink@gmail.com> writes:
> Hello Vincent,
>
> Vincent Truchseß <debian-user@v-tr.org> writes:
>
>> I've had the same Issue here delegating prefixes to my VPN-Gateway in my
>> home-hetwork.
>
> Good to know that it's not just me. For posterity, I did some further
> tests:
>
> * It does not matter if the router sets the "Other Configuration" or the
> "Managed" flags, as long as I use "ForceDHCPv6PDOtherInformation=yes"
> in systemd-networkd. The behavior is the same.
>
> * Playing around with tcpdump, I found that while a new prefix on my
> external interface enp3s0 is announced (and received) correctly via
> router advertisement, neither the ISP's router nor systemd-networkd
> trigger any DHCPv6 activity. I am not sure about the relevant RFCs and
> if a change in prefix should trigger a DHCPv6 Solicit or if the router
> has to send some other message, but as far as I understand, the router
> advertisement should be enough. The server *could* send Reconfigure
> messages, but my ISP's router does not seem to do it.
>
> * Nevertheless, when systemd-networkd sends out a solicit or renew and
> the DHCPv6 server answers with NoBinding, the client is supposed to
> send a request message to try to get another prefix in reply (at least
> that's how I read RFC 8415, Sec. 18.2.10.1). It does not do this.
>
> I also tried with the systemd-networkd from yesterday's git master of
> the systemd git repo, but it behaves the same in my limited testing. I
> strongly assume systemd-networkd is still buggy in this area.
>
> An additional problem is that the routes for old prefixes do not seem to
> be removed. That might also lead to problems.
>
>> My solution back then was to ditch systemd-networkd for this setup and
>> rely on configuring dhcpcd and radvd accordingly. Systemd's
>> DHCP-implementation seems to a little bit out of whack, depending on the
>> version.
>>
>> Unfortunately that VPN-Gateway got decommissioned and I don't have a
>> backup of those two config-files. If I remember right, I kept the config
>> close to what the ArchLinux-Wiki suggests.
>
> Thanks for the info, but I will rather contact systemd upstream about
> this, so that this software can be fixed. I found it to be a very
> pleasant network managing daemon with very clear configuration and
> otherwise quite a bit more reliable than NetworkManager or ifupdown, so
> I think improving it is the better long-term solution.
>
> Tobias
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