Netplan has no option to enable dhcpv6 prefix delegation like ifupdown did

[Bryce Larson]

When using ifupdown, you can put 'request_prefix 1' in order to specify for dhclient to request an dhcpv6 prefix delegation. I also understand that systemd-networkd also supports this, see https://github.com/systemd/systemd/issues/1080 If netplan is to fully replace ifupdown feature for feature, it needs to support this functionality as I am using that feature with ifupdown and cannot upgrade to netplan without it.

I understand from the netplan.io website that you guys want cases like this to be reported here. Let me know if that is not the case or if there is a better place to put things like this.

[Bryce Larson (bryceml)]

Another thing that relates to this is the ability to specify what the duid is that is sent in the dhcpv6 request. If I recall correctly systemd-networkd offers the ability to specify the duid.

[Ryan Harper (raharper)]

Hi Bryce,

Thanks for taking the time to report this issue.

netplan doesn't yet support setting dhcpv6 prefix delegation. Thanks for the link.

The relevant networkd sections are available and documented here:

https://www.freedesktop.org/software/systemd/man/systemd.network.html

IPv6PrefixDelegation=

[IPv6PrefixDelegation] Section Options

We'll need to see what, if any support for this there is in NetworkManager and then determine what key/values to use to control and then add support to the backend renders.

W.r.t the DUID, networkd currently sends an RFC4361-compliant Client ID, which is the combination of IAID and DUID; this is generated automatically by systemd. If you need to override this value currently you need to create a global override to /etc/systemd/network.conf, details here.

https://www.freedesktop.org/software/systemd/man/networkd.conf.html#

That's not currently modeled in the yaml or backends either.

[Wladimir Mutel (mwg)]

1 year has definitely passed since the release of Ubuntu 18.04
netplan had been updated through 0.36 -> 0.40 -> 0.97 -> 0.98
any progress in supporting dhcp6-pd there ???

[John Ioannidis (ubuytu)]

It's now 2020. I really have to ask: who writes networking software, let alone making it the default, and does not consider fully-supporting IPv6 a requirement?

[John Ioannidis (ubuytu)]

When will this be fixed? Why was netplan made the default when it does not have feature parity with ifupdown? Why is this question being ignored?

[Konstantin Novitsky (novitk)]

+1
Gave up on Ubuntu in a router/network appliance space due to this. Sure, I can remove netplan and use ifupdown, but why bother when openwrt just works!

[Wladimir Mutel (mwg)]

Fortunately, with systemd-networkd + wpa_supplicant you could go without any of {netplan, ifupdown, NetworkManager} on both modern Ubuntu or modern Debian. As you may imagine, netplan is just a frontend generating ("rendering") configs for one of possible backends within {networkd, NetworkManager}. So you just copy /run/systemd/network/* into /etc/systemd/network/ , after which you may remove all netplan and related packages and go ahead with systemd-networkd only (which, unfortunately, is nailed to the core of modern Linuxes pretty firmly and not that easily detachable).

[David Burrow (dnburrow)]

Would still love to see IPv6-PD implemented in netplan.

[DanyChen (danychen)]

I have this problem too, netplan has so many ancient bugs that are still open, I don't know why ubuntu integrate netplan, why don't make cloud-init just write networkd config files.

[Avamander (avamander)]

Well this is an annoying bug, makes netplan useless for the biggest IPv6 ISP in the country.

[Mike Borsetti (mborsetti)]

Ugly workaround until this bug is fixed, but this seems to work with Ubuntu 20.04.3 LTS and 21.04. It's executed at startup, e.g. from rc.local, as root; br0 in this case is the interface to a WAN network so adapt to your system before running.

echo "IPv6SendRA=yes" >> /run/systemd/network/10-netplan-br0.network
echo "DHCPv6PrefixDelegation=yes" >> /run/systemd/network/10-netplan-br0.network
echo "IPv6PrivacyExtensions=yes" >> /run/systemd/network/10-netplan-br0.network
systemctl restart systemd-networkd
/usr/lib/systemd/systemd-networkd-wait-online

Yes, it's ugly and am sure breaks a whole lot of Netplan's goals, but at this point is Netplan that breaks the goal of having a prefix-delegated network so it's a (much) lesser evil IMHO.

[Lukas Märdian (slyon)]

A more elegant way to implement this workaround would probably be to put that configuration snippet into a drop-in override (as described here https://www.freedesktop.org/software/systemd/man/systemd.network.html), e.g.:

$ cat /etc/systemd/network/10-netplan-br0.network.d/override.conf
[Network]
IPv6SendRA=yes
DHCPv6PrefixDelegation=yes
IPv6PrivacyExtensions=yes

[Mike Borsetti (mborsetti)]

Lukas,

Thank you!

For the benefit of others, the drop-in file must have appropriate section headers, so the correct file is as follows:

$ cat /etc/systemd/network/10-netplan-br0.network.d/ipv6_pd_ra.conf
[Network]
IPv6SendRA=yes
DHCPv6PrefixDelegation=yes

If the ISP gives you a /60 (or /48, /52, /56) prefix delegation on request, and you want one, then the following works (ISP-specific, YMMV):

$ cat /etc/systemd/network/10-netplan-enp1s0.network.d/ipv6_pd.conf
[DHCPv6]
PrefixDelegationHint=::/60

[Sifr Moja (simplexion)]

Why is the importance of this set to wishlist? Why is IPv6 seen as a second class citizen in this?

[Erik Nygren (erik+ubuntu)]

The version of systemd-networkd in Ubuntu 22.04 makes substantial improvements to DHCPv6-PD support and addresses lots of the shortcomings in 20.04. I've written up some details on how to configure this via overrides:

https://erik.nygren.org/dhcpv6-pd-on-ubuntu-2204.html

It would be vastly preferable if this was just exposed via netplan.
Note that the syntax of the configuration changed in recent versions of systemd-networkd (ie, some things moved into distinct stanzas).

[Mike Borsetti (mborsetti)]

Hi Erik,

Great write-up (thanks!).

Just as an FYI, going through it I found that it includes the "ForceDHCPv6PDOtherInformation" directive, which is not a known networkd directive per https://www.freedesktop.org/software/systemd/man/systemd.network.html. Indeed it has been deprecated per https://github.com/systemd/systemd/issues/22493.