[systemd-devel] systemd-networkd: IPForward with ipv6

[Lennart Poettering]

On Wed, 03.06.15 19:18, Sébastien Luttringer (seblu at seblu.net) wrote:

> Hello,
> 
> Since systemd v220, IPForward= parameter in [Network] set kernel
> parameters by interface (/proc/sys/net/ipv[46]/conf/*/forwarding).
> This is nice and works perfectly for ipv4.
> 
> Unfortunately, ipv6 forwarding doesn't works until we manually set
> /proc/sys/net/ipv6/conf/all/forwarding to 1.

Are you saying that /proc/sys/net/ipv6/conf/$interface/forwarding is a
NOP in the kernel for anything except $interface being "all"?

That sounds seriously broken in the kernel. They should not expose a
setting that is a NOP like that...

> 
> In term of user experience, IPforward=ipv6 doesn't enable ipv6
> forwarding on the interface. That's tricked me.
> 
> From:
> https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt
> 
> conf/all/forwarding - BOOLEAN
>         Enable global IPv6 forwarding between all interfaces.
> 
>         IPv4 and IPv6 work differently here; e.g. netfilter must be
> used
>         to control which interfaces may forward packets and which not.
> 
> An maybe better explained here:
> http://www.tldp.org/HOWTO/Linux+IPv6-HOWTO/proc-sys-net-ipv6..html

This documentation is not particularly good, but it certainly doesn't
suggest the option was a NOP. 

Can you elaborate on this?

Do you have any references that clarify that IPv6 and IPv4 handling of
this setting is really different?

Lennart

-- 
Lennart Poettering, Red Hat