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

[Jeffrey Walton <noloader@gmail.com>]

On Sat, Jan 10, 2026 at 11:30 AM Reinder <reinder@reinder.nl> wrote:
>
> Hello Debian Users!
>
> Maybe I am doing something silly, but I am confused, so please educate
> me if I am seeing/doing this wrong.
>
> When trying to disable automatic binding of a (wrongly) advertised ipv6
> IP I got stuck and only got it to work with the bottom two lines below
> in my /etc/sysctl.d/am-no-ipv6.conf:
>
> root@reinder:~# cat /etc/sysctl.d/am-no-ipv6.conf
> net.ipv6.conf.all.accept_ra=0
> net.ipv6.conf.all.autoconf=0
> net.ipv6.conf.default.accept_ra=0
> net.ipv6.conf.default.autoconf=0
> net.ipv6.conf.ens18.accept_ra=0
> net.ipv6.conf.ens19.accept_ra=0
> root@reinder:~#
>
> This is, to me, unexpected, even unwanted behavior?
> I would expect disabling default and all to work and prevent ipv6
> routing and perhaps need of firewalling?!

Is the package linux-sysctl-defaults installed?  See
<https://www.debian.org/releases/trixie/release-notes/issues.html#etc-sysctl-conf-is-no-longer-honored>.

Also, which version of Debian?

> What I also tried before and still have access but does not prevent an
> ipv6 from binding:
>
> root@reinder:~# tail -7 /etc/dhcpcd.conf
> ## only ipv4
> ipv4only
> ipv6ra_noautoconf
> nodhcp6
> noipv6
> noipv6rs
> noipv4ll
> root@reinder:~#
>
> root@reinder:~# cat /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
>          autoconf 0
>          accept_ra 0
>
> # The secondary network interface
> allow-hotplug ens19
> iface ens19 inet dhcp
> iface ens19 inet6 static
>          autoconf 0
>          accept_ra 0
> root@reinder:~#

Jeff