Re: Question about NetBSD implementation of IPv6 SLAAC and RFC4941

[Roy Marples <roy%marples.name@localhost>]

On 07/04/2020 22:22, Christos Zoulas wrote:
> > On Apr 7, 2020, at 5:15 PM, Roy Marples <roy%marples.name@localhost> wrote:
> >
> > On 06/04/2020 21:25, Christos Zoulas wrote:
> > > > On Apr 5, 2020, at 9:35 PM, Roy Marples <roy%marples.name@localhost> wrote:
> > > >
> > > > Ah, now we are getting interesting! So, some questions:
> > > >
> > > > 1) Are you soliciting a router or just waiting for an RA to magically appear?
> > > >    This is fairly important as recent RFC 7772 vastly reduces broadcasts to the
> > > >    network - it unicasts a lot more than it broadcasts - and makes each node
> > > >    wanting a router actually solicit one.
> > > >    If you're not using dhcpcd to solicit, what are you using?
> > > I am not doing anything special. I just set ip6mode=autohost in rc.conf which does:
> > >                  /sbin/sysctl -qw net.inet6.ip6.accept_rtadv=1
> > > and I am all set.
> >
> > The default maximum time from one RA to the next without solicition is 600 seconds, the upport limit is 1800 seconds.
> >
> > Now, if your IPv6 routers don't support RFC 7772 and there are many IPv6 nodes soliciting a RA (you'll get a RA every 3 seconds or so) or are configured with a low MaxRtrAdvInterval then that explains why it "works" for you.
> >
> > Given an IPv6 router which supports RFC 7772, I wouldn't want to wait 10 minutes (default, max 30 minutes) after userland has booted before network connectivity comes up (assuming IPv6 is required for connectivity). And frankly if anyone submitted a bug report for this I would just tell them to solicit a RA because that's how IPv6 is designed.
> >
> > Is this something we want to support?
>
> I am not sure. Do you mean running dhcpcd with the right flags to behave like rtsold?

Yes

dhcpcd -T6 --nodhcp6 $interface

gets you the same behaviour as rtsol, keeping RA in the kernel.

dhcpcd -6 --nodhcp6 $interface

gets you the same, just puts the RA handling in dhcpcd, although you should 
probably drop the nodhcp6 option so the dhcpcd can respect the M or O flags if 
set in the RA.

We're at the point where something in userland needs to solicit an RA to 
guarantee connectivity ASAP - unless everything is static of course (but then we 
don't care about RA's here). I would rather have something that solicits the RA 
actually process the RA. Which makes sense because the RDNSS and DNSSL options 
within a RA need to be written to resolv.conf(5).

> Fixing the kernel to support RFC 7772?

Our rtadvd(8) has supported RFC 7772 since NetBSD-9.
It's not a kernel thing, it's how a router sends RA's.

Roy