systemd-networkd can't set ip6tnl interface mode as any

[Yakov Shiryaev]

systemd-networkd provides "Mode=" configuration for a virtual device of "Kind=ip6tnl". But setting mode to "any" doesn't work, tunnel mode stay as ipv6/ipv6:

20/05/21 18:08:33 darkyman@mnt-myt-focal ~ > ip -6 tun show
ip6tnl0: ipv6/ipv6 remote :: local :: encaplimit 0 hoplimit inherit tclass 0x00 flowlabel 0x00000 (flowinfo 0x00000000)

I'm expecting it to be in any/ipv6 mode like:

ip6tnl0: any/ipv6 remote :: local :: encaplimit 0 hoplimit inherit tclass 0x00 flowlabel 0x00000 (flowinfo 0x00000000)

Config file attached (00-ip6tnl0.netdev), I'm using systemd `systemd 245 (245.4-4ubuntu3.6)` on a `Ubuntu 20.04.2 LTS`.
Currently I'm using systemd service as a workaround this issue, which sets mode to "any" by calling

/usr/sbin/ip -6 tunnel change ip6tnl0 mode any

And that's what networkctl thinks about this tunnel interface

● 7: ip6tnl0
             Link File: /usr/lib/systemd/network/99-default.link
          Network File: /etc/systemd/network/01-ip6tnl0.network
                  Type: tunnel6
                 State: degraded (configured)
                   MTU: 9000 (min: 68, max: 65407)
  Queue Length (Tx/Rx): 1/1
               Address: fe80::3063:1eff:febf:8aaa

May 20 17:55:36 mnt-myt-focal.example.com systemd-udevd[1062]: ip6tnl0: Could not generate persistent MAC: No data available
May 20 17:55:36 mnt-myt-focal.example.com systemd-networkd[1008]: ip6tnl0: netdev ready
May 20 17:55:36 mnt-myt-focal.example.com systemd-networkd[1008]: ip6tnl0: netdev could not be created: Invalid argument
May 20 17:55:36 mnt-myt-focal.example.com systemd-networkd[1008]: ip6tnl0: IPv6 successfully enabled
May 20 17:55:36 mnt-myt-focal.example.com systemd-networkd[1008]: ip6tnl0: Link UP
May 20 17:55:36 mnt-myt-focal.example.com systemd-networkd[1008]: ip6tnl0: Gained carrier
May 20 17:55:36 mnt-myt-focal.example.com systemd-networkd[1008]: ip6tnl0: Gained IPv6LL

[Nick Rosbrook (enr0n)]

Is this still an issue? If so, can you please enable debug logs on systemd-networkd, and then reboot, and attach those recent logs?

$ systemctl edit systemd-networkd.service
# Add the following when the editor opens:
[Service]
Environment=SYSTEMD_LOG_LEVEL=debug

$ reboot
[...]
$ journalctl -b -u systemd-networkd.service > logs.txt

[Launchpad Janitor (janitor)]

[Expired for systemd (Ubuntu) because there has been no activity for 60 days.]