linux 4.0-2
systemd 219-6

Now effects both ipv4 and ipv6 settings.

Note:

$ systemctl is-enabled systemd-sysctl.service
static

$ systemctl status sysinit.target
● sysinit.target - System Initialization
Loaded: loaded (/usr/lib/systemd/system/sysinit.target; static; vendor preset: disabled)
Active: active since Thu 2015-04-23 12:44:01 MDT; 26min ago
Docs: man:systemd.special(7)

Apr 23 12:44:01 topaz systemd[1]: Reached target System Initialization.
Apr 23 12:44:01 topaz systemd[1]: Starting System Initialization.

$ strace -e open /usr/lib/systemd/systemd-sysctl 2>&1 | grep \\.conf
open("/etc/sysctl.d/30-ipforward.conf", O_RDONLY|O_CLOEXEC) = 4
open("/usr/lib/sysctl.d/50-coredump.conf", O_RDONLY|O_CLOEXEC) = 4
open("/usr/lib/sysctl.d/50-default.conf", O_RDONLY|O_CLOEXEC) = 4

$ find /usr/lib/systemd/ -name "*systemd-sysctl*"
/usr/lib/systemd/system/systemd-sysctl.service
/usr/lib/systemd/system/sysinit.target.wants/systemd-sysctl.service
/usr/lib/systemd/systemd-sysctl

Immediately after boot:

$ sudo sysctl -a|grep forw
net.ipv4.conf.all.forwarding = 1
net.ipv4.conf.all.mc_forwarding = 0
net.ipv4.conf.default.forwarding = 1
net.ipv4.conf.default.mc_forwarding = 0
net.ipv4.conf.enp0s7.forwarding = 0
net.ipv4.conf.enp0s7.mc_forwarding = 0
net.ipv4.conf.enp4s0.forwarding = 0
net.ipv4.conf.enp4s0.mc_forwarding = 0
net.ipv4.conf.lo.forwarding = 1
net.ipv4.conf.lo.mc_forwarding = 0
net.ipv4.ip_forward = 1
net.ipv4.ip_forward_use_pmtu = 0
net.ipv6.conf.all.forwarding = 1
net.ipv6.conf.default.forwarding = 1
net.ipv6.conf.enp0s7.forwarding = 0
net.ipv6.conf.enp4s0.forwarding = 0
net.ipv6.conf.lo.forwarding = 1
[ 48.494836] nr_pdflush_threads exported in /proc is scheduled for removal

Subsequent to boot, run manually:

$ sudo sysctl --system
* Applying /etc/sysctl.d/30-ipforward.conf ...
net.ipv4.conf.all.forwarding = 1
net.ipv4.conf.default.forwarding = 1
net.ipv4.conf.enp0s7.forwarding = 1
net.ipv4.conf.enp4s0.forwarding = 1
net.ipv4.conf.lo.forwarding = 1
net.ipv4.ip_forward = 1
net.ipv6.conf.default.forwarding = 1
net.ipv6.conf.all.forwarding = 1
net.ipv6.conf.enp0s7.forwarding = 1
net.ipv6.conf.enp4s0.forwarding = 1
net.ipv6.conf.enp0s7.accept_ra = 2
* Applying /usr/lib/sysctl.d/50-coredump.conf ...
kernel.core_pattern = |/usr/lib/systemd/systemd-coredump %p %u %g %s %t %e
* Applying /usr/lib/sysctl.d/50-default.conf ...
kernel.sysrq =16
kernel.core_uses_pid = 1
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.default.accept_source_route = 0
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.default.promote_secondaries = 1
net.ipv4.conf.all.promote_secondaries = 1
net.core.default_qdisc = fq_codel
fs.protected_hardlinks = 1
fs.protected_symlinks = 1
* Applying /etc/sysctl.conf ...
sysctl: cannot open "/etc/sysctl.conf": No such file or directory

Could systemd-networkd be interfering?

Bug 89509 - systemd-networkd: net.ipv4.conf.default.forwarding is ignored in 219
https://bugs.freedesktop.org/show_bug.cgi?id=89509

"Yeah this was an underdocumented change in 219: we manage the IP forwarding setting per interfac now. You have to set IPForward=yes in the .network files explicitly now, otherwise you will not get IP forwarding on that interface."

Seriously?!

"Either way, Tom really needs to sign off on this."

So then, Tom gets to decide personally, for the entire world-wide Linux-using community, whether to unilaterally "break" sysctl?

Seriously?!  Something like "the poster child for 'arrogant'" comes to mind...

(In reply to James from comment #2)
>
> So then, Tom gets to decide personally, for the entire world-wide
> Linux-using community, whether to unilaterally "break" sysctl?

Nope. I make the change in networkd. And it's not for the "entire world-wide Linux-using community", but only for those who decide to use networkd for network management.

*** This bug has been marked as a duplicate of bug 89509 ***

(In reply to Lennart Poettering from comment #3)
> (In reply to James from comment #2)
> >
> > So then, Tom gets to decide personally, for the entire world-wide
> > Linux-using community, whether to unilaterally "break" sysctl?
> 
> Nope. I make the change in networkd. And it's not for the "entire world-wide

Oops, wanted to say "I *made* that change in networkd".