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

[Reinder <reinder@reinder.nl>]

On 2026-01-12 20:04, Greg Wooledge wrote:
> On Mon, Jan 12, 2026 at 11:44:37 -0500, Jeffrey Walton wrote:
> > On Sun, Jan 11, 2026 at 4:58 AM Reinder <reinder@reinder.nl> wrote:
>
> They might be using isc-dhcp-client instead.  My trixie system is using
> that, but it was installed on an older release and upgraded.  I don't
> know what a new trixie installation uses for its DHCP client.

No it is indeed a fresh trixie with dhcpcd+ifupdown.

The issue is "resolved" and I'm sure it is in ifupdown.

There seem to be three ways to work around it, one is to include 
addr_gen_mode=1 in sysctl settings for all/default.
net.ipv6.conf.all.accept_ra=0
net.ipv6.conf.all.autoconf=0
net.ipv6.conf.all.addr_gen_mode=1
net.ipv6.conf.default.accept_ra=0
net.ipv6.conf.default.autoconf=0
net.ipv6.conf.default.addr_gen_mode=1

The other one was to set accept_ra = 0 / autoconf = 0 on a dev device 
inet6 manual/static in /etc/network/interfaces.

The third is to force the specific interfaces in sysctl/kernel cmdline:
net.ipv6.conf.ens18.accept_ra=0
net.ipv6.conf.ens19.accept_ra=0

I am quite sure it is ifupdown always setting accept_ra=1 on a device 
that has no inet6 configured in /etc/network/interfaces and ignoring the 
kernel settings all/default to 0 for accept_ra/autoconf.
But I haven't checked the code. If you guys think it's worth the time 
and is something that should be patched I can maybe find some time later 
for this.