[systemd-devel] networkd 249.11 fails to create ip6gre and vti6 tunnels

[Mantas Mikulėnas]

Kernel and systemd changes aside, I kind of want to say that you need to
specify an interface for the link-local endpoint to be bound to – just as
with regular sockets. If the tunnel were device-bound and not independent,
that would happen by default.

It also seems weird that the tunnel has endpoints with different scopes; I
think I've seen routers reject such packets with a "Scope Mismatch" error.

I would try building systemd from Git source; if I remember correctly,
systemd-networkd could be run directly from the build directory, making it
possible to `git bisect` down to the change that fixed this.

On Mon, Nov 27, 2023, 19:38 Danilo Egea Gondolfo <
danilo.egea.gondolfo at gmail.com> wrote:

> Hello,
>
> I'm looking for help to understand an issue we are observing on Ubuntu
> 22.04.
>
> networkd is failing with "netdev could not be created: Invalid argument"
> when I try to create either an ip6gre or vti6 device.
>
> We believe this problem started when we pulled this change [1] in to the
> kernel 5.15. The problem also happens with the most recent upstream kernel
> so it's not an issue introduced by Ubuntu.
>
> The problem doesn't happen on recent versions of systemd but we'd like to
> fix it on systemd 249 (used by Ubuntu 22.04).
>
> How to reproduce the problem (tested on Ubuntu 22.04 (jammy) with systemd
> 249.11-0ubuntu3.11 and kernel 5.15.0-89-generic):
>
> --- /etc/systemd/network/tun0.netdev ---
> [NetDev]
> Name=tun0
> Kind=ip6gre
>
> [Tunnel]
> Independent=true
> Local=fe80::1
> Remote=2001:dead:beef::2
> ------
>
> --- /etc/systemd/network/tun0.network ---
> [Match]
> Name=tun0
>
> [Network]
> LinkLocalAddressing=ipv6
> ConfigureWithoutCarrier=yes
> ------
>
> After restarting networkd I see this in the logs
> tun0: netdev could not be created: Invalid argument
> tun0: netdev removed
>
> If we boot a kernel that doesn't have [1], the interface tun0 is created.
>
> Here is the full log with debug enabled
> https://paste.ubuntu.com/p/dPbPxgRThW/
>
> As I said, the problem seems to be fixed already in systemd, but I'm
> looking for help to understand what changes fixed it.
> The theory is that the netlink attributes used to configure the tunnel
> local/remote IPs might be wrong.
>
> This problem is documented here
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2037667
>
> Thanks in advance.
>
> [1] -
> https://github.com/torvalds/linux/commit/b0ad3c179059089d809b477a1d445c1183a7b8fe
>
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