Why system reports "permission denied on key" while setting the kernel parameter "net.ipv4.conf.all.mc_forwarding" ?

Issue

• Why system reports "permission denied on key" while setting the kernel parameter net.ipv4.conf.all.mc_forwarding or net.ipv6.conf.all.mc_forwarding?

# sysctl -w net.ipv4.conf.all.mc_forwarding=1
error: "Permission denied" setting key "net.ipv4.conf.all.mc_forwarding"

# echo 1 > /proc/sys/net/ipv4/conf/all/mc_forwarding
bash: /proc/sys/net/ipv4/conf/all/mc_forwarding: Permission denied

• Setting net.ipv4.conf.all.mc_forwarding to zero is failing with the following message:

-- Unit systemd-sysctl.service has begun starting up.
Aug 19 16:30:56 fl1-tst-x.y.z  systemd-sysctl[3603]: Failed to write '0' to '/proc/sys/net/ipv4/conf/all/mc_forwarding': Permission denied
Aug 19 16:30:56 fl1-tst-x.y.z  systemd[1]: systemd-sysctl.service: main process exited, code=exited, status=1/FAILURE
Aug 19 16:30:56 fl1-tst-x.y.z systemd[1]: Failed to start Apply Kernel Variables.
-- Subject: Unit systemd-sysctl.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit systemd-sysctl.service has failed.
-- 
-- The result is failed.
Aug 19 16:30:56 fl1-tst-x.y.z systemd[1]: Unit systemd-sysctl.service entered failed state.