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It is currently impossible to enable ipv6 forwarding on a per-interface basis like in ipv4. To enable forwarding on an ipv6 interface we need to enable it on all interfaces and disable it on the other interfaces using a netfilter rule. This is especially cumbersome if you have lots of interfaces and only want to enable forwarding on a few. According to the sysctl docs [0] the `net.ipv6.conf.all.forwarding` enables forwarding for all interfaces, while the interface-specific `net.ipv6.conf.<interface>.forwarding` configures the interface Host/Router configuration. Introduce a new sysctl flag `force_forwarding`, which can be set on every interface. The ip6_forwarding function will then check if the global forwarding flag OR the force_forwarding flag is active and forward the packet. To preserve backwards-compatibility reset the flag (on all interfaces) to 0 if the net.ipv6.conf.all.forwarding flag is set to 0. Add a short selftest that checks if a packet gets forwarded with and without `force_forwarding`. [0]: https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com> Signed-off-by: Gabriel Goller <g.goller@proxmox.com> Link: https://patch.msgid.link/20250722081847.132632-1-g.goller@proxmox.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>