Re: net.ipv6.conf.all.accept_ra=0 net.ipv6.conf.default.accept_ra=0 not working?!

[Jeffrey Walton <noloader@gmail.com>]

On Sun, Jan 11, 2026 at 4:58 AM Reinder <reinder@reinder.nl> wrote:
>
> >
> > At the moment I am thinking maybe ifup is still doing something? Though
> > there is no inet6 configuration in /etc/network/interfaces:
> >
> It seems to be indeed an ifupdown issue, forcing a static ipv6 in
> /etc/network/interfaces works, see below.
> Problem is I did not want to do this. Will debug some more.

If I am not mistaken... If you are not using NetworkManager, and you
are not using Systemd, and you are not using Kea, then you are
probably using dhcpcd-base+ifupdown.

Maybe there's something in dhcpcd-base that will provide the next path
to go down.

> root@reinder:~# sysctl -a | grep accept_ra\
> net.ipv6.conf.all.accept_ra = 0
> net.ipv6.conf.default.accept_ra = 0
> net.ipv6.conf.ens18.accept_ra = 0
> net.ipv6.conf.ens19.accept_ra = 1
> net.ipv6.conf.lo.accept_ra = 1
> root@reinder:~# sed 's#[0-9]*:*:*:*:*:#xx:xx:xx:xx:xx:#'
> /etc/network/interfaces
> # This file describes the network interfaces available on your system
> # and how to activate them. For more information, see interfaces(5).
>
> source /etc/network/interfaces.d/*
>
> # The loopback network interface
> auto lo
> iface lo inet loopback
>
> # The primary network interface
> allow-hotplug ens18
> iface ens18 inet dhcp
> iface ens18 inet6 static
>          address xx:xx:xx:xx:xx:7b8:627:2::d59a:fd8c/64
>          autoconf 0
>          accept_ra 0
>
> # The secondary network interface
> allow-hotplug ens19
> iface ens19 inet dhcp
> root@reinder:~# ip a s dev ens18|grep kernel_ra|sed
> 's#[0-9]*:*:*:*:*:#xx:xx:xx:xx:xx:#'
> root@reinder:~#
>