Re: "accept_ra 1" vs "accept_ra 2" in interfaces configuration-file

[Martin T <m4rtntns@gmail.com>]

On Tue, Aug 21, 2018 at 1:23 AM Andy Smith <andy@strugglers.net> wrote:
>
> Hi Martin,
>
> On Mon, Aug 20, 2018 at 03:58:36PM +0300, Martin T wrote:
> > On Mon, Aug 20, 2018 at 7:55 AM Andy Smith <andy@strugglers.net> wrote:
> > > Back in 2011 this was a hard-won battle:
> > >
> > >     http://strugglers.net/~andy/blog/2011/09/04/linux-ipv6-router-advertisements-and-forwarding/
>
> […]
>
> > Thanks for this very informative blog post! However, setting the
> > "net.ipv6.conf.all.forwarding" to 1 in /etc/sysctl.conf and
> > "accept_ra" to 2 in /etc/network/interfaces for ISP facing
> > interface(eth0) didn't work for me. I expected SLAAC to work, but it
> > didn't. I'm running kernel version 4.9.0.
>
> Strange. I've had a look and it seems I continued to use the
> workaround mentioned in the blog post even though supposedly I no
> longer need to. If you use that workaround, does it (SLAAC) start
> working for you?
>
> Also, is it just address assignment that doesn't work or is it also
> default router assignment that doesn't work? On my servers that
> forward v6 I don't use dynamic assignment of addresses, I statically
> assign them, but I do use dynamic assignment of default route.
>
> Cheers,
> Andy
>

Hi Andy,


Thanks for your reply!

> If you use that workaround, does it (SLAAC) start working for you?

Do you mean the pre-up statements in /etc/network/interfaces? If yes,
then with those workarounds the SLAAC works, i.e I get the default
route. My ISP-facing interface is eth0 and it has forwarding disabled:

# cat /proc/sys/net/ipv6/conf/eth0/forwarding
0
#


Rest of the options are set:

# cd /proc/sys/net/ipv6/conf/
# cat default/forwarding
1
# cat all/forwarding
1
# cat eth0/accept_ra
2
# cat all/accept_ra
1
# cat default/accept_ra
1
#


However, I quite do not understand how returned IPv6 traffic(ingress
traffic to eth0) is routed to my LAN-facing interface when I have
disabled it in /proc/sys/net/ipv6/conf/eth0/forwarding? If I do the
same for IPv4 traffic(echo 0 >
/proc/sys/net/ipv4/conf/eth0/forwarding), then returned traffic is
dropped because forwarding for eth0 is disabled. In addition,
"accept_ra" with a value of 2 should ensure that RA messages are
accepted even if forwarding for that interface is enabled, shouldn't
it?

> Also, is it just address assignment that doesn't work or is it also
> default router assignment that doesn't work? On my servers that
> forward v6 I don't use dynamic assignment of addresses, I statically
> assign them, but I do use dynamic assignment of default route.

I have exactly the same case. I use dynamic assignment only for
default route and this doesn't work even if "accept_ra" has a value of
2.


thanks,
Martin