[systemd-devel] systemd-networkd: IPv6 prefix delegation disabled by ipv6forwarding=true

[Kevin P. Fleming]

On Mon, Jan 13, 2025, at 12:58, Barry Scott wrote:

> This sets net.ipv6.conf.all.forwarding = 1 but, prefix delegation is broken.
>
> If I remove Ipv6Forwarding=true and then set 
> net.ipv6.conf.all.forwarding = 1 mnaually forwarding works.

It could be useful to note that this setting does not actually enable or disable forwarding of IPv6 packets! I learned this recently after upgrading to systemd 257, where the option names have changed to better reflect what they actually do (the behavior is not new, the names were just always misleading).

This kernel setting sets the IPv6 stack to 'host' mode or 'router' mode, which carries with it a few other settings. If you read the release notes for systemd 256/257 you'll get a better understanding of what they actually do... and yes, they do affect prefix delegation.