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.br...@gmail.com> writes: > Hello Vincent, > > Vincent Truchseß <debian-u...@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
