I've been recently playing with IPv6 but I have a vexing problem with my
little Ubuntu box. Systemd-networkd (from systemd 245.4) is supposed to
understand a directive like this:

IPv6Token=prefixstable:my_prefix

where my_prefix is exactly what my router sends in its RA, 64 bits,
ending in a double colon (::), verified by tcpdump. And what I wish to
get out of this is an IPv6 address generated as described in RFC7217,
i.e. a stable address where the lower 64 bits are not based on my MAC
address.

Unfortunately systemd-networkd does not seem to agree. It accepts the
directive without comment but I still get the EUI-64 address. Even if I
set log level to debug there's nothing in the log about this. I've tried
other forms in my_prefix but then networkd eagerly tells me it's wrong
but not what would be correct and actually *work*.

I can work around this in a bunch of ways so not looking for that,
but getting this to work would be easiest.

I looked but I haven't found any bug reports about this so I have a
feeling it should work. Any ideas?

Am 02.11.2022 um 16:16:12 Uhr schrieb Anssi Saari:

> where my_prefix is exactly what my router sends in its RA, 64 bits,
> ending in a double colon (::), verified by tcpdump. And what I wish to
> get out of this is an IPv6 address generated as described in RFC7217,
> i.e. a stable address where the lower 64 bits are not based on my MAC
> address.
>
> Unfortunately systemd-networkd does not seem to agree. It accepts the
> directive without comment but I still get the EUI-64 address. Even if
> I set log level to debug there's nothing in the log about this. I've
> tried other forms in my_prefix but then networkd eagerly tells me
> it's wrong but not what would be correct and actually *work*.

Is netplan still active?
Please show your netplan config.

Marco Moock <mo01@posteo.de> writes:

> Is netplan still active?
> Please show your netplan config.

I know next to nothing about netplan so it probably has a default
config. I guess it's active since I have a
/run/systemd/network/10-netplan-eth0.network with this content:

[Match]
Name=eth0

[Link]
RequiredForOnline=no

[Network]
DHCP=ipv4
LinkLocalAddressing=ipv6

[DHCP]
RouteMetric=100
UseMTU=true

Does this override whatever I have in /etc/systemd/network/eth0.network
or? Or in fact, I don't really have anything there, except for
IPv6Token=.

There's also /etc/netplan/50-cloud-init.yaml with this:

# This file is generated from information provided by the datasource. Changes
# to it will not persist across an instance reboot. To disable cloud-init's
# network configuration capabilities, write a file
# /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the following:
# network: {config: disabled}
network:
ethernets:
eth0:
dhcp4: true
optional: true
version: 2

These seem to somewhat match what was put into
/run/systemd/network/10-netplan-eth0.network.

So what happens if I remove the netplan package(s)? Nothing works or
things actually start working the way I expect? Assuming I have a
complete /etc/systemd/network/eth0.network, that is.

Can I edit that file under /run for testing and restart
systemd-networkd?

Am 02.11.2022 um 17:19:40 Uhr schrieb Anssi Saari:

> There's also /etc/netplan/50-cloud-init.yaml with this:
>
> # This file is generated from information provided by the datasource.
> Changes # to it will not persist across an instance reboot. To
> disable cloud-init's # network configuration capabilities, write a
> file # /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the
> following: # network: {config: disabled}
> network:
> ethernets:
> eth0:
> dhcp4: true
> optional: true
> version: 2

Only place the following in /etc/netplan/50-cloud-init.yaml

network:
version: 2
renderer: networkd

Then "sudo netplan try".
Then restart the OS and check if networkd does what you like.

Marco Moock <mo01@posteo.de> writes:

> Am 02.11.2022 um 17:19:40 Uhr schrieb Anssi Saari:

> Only place the following in /etc/netplan/50-cloud-init.yaml
>
> network:
> version: 2
> renderer: networkd
>
> Then "sudo netplan try".
> Then restart the OS and check if networkd does what you like.

Brilliant, thanks. At least temporarily it's exactly what I needed and
IPv6Token=prefixstable:myprefix works exactly as the manual says.

I'll save the reboot for when I'm at the system and can access the
serial console, just in case.