Re: IPv6 default routes / NM vs. kernel autoconfig

[Pavel Simerda <psimerda redhat com>]

> > Though a router did a somewhat surprising thing (coming up with a
> > different link-local address), the network here is working
> > perfectly
> > well.
> NM *should* remove any routes it added if the most recent RA for that
> router has a lifetime of 0.  That's a bug in NM, and something we
> should
> fix.

I filed it as:

https://bugzilla.gnome.org/show_bug.cgi?id=680891

It covers both changing routers and deconfiguration. This is a known bug,
I just haven't documented it before.

> > > > We took a look at the router, and found that, before reboot, it
> > > > had
> > > > been
> > > > using blahblah:dcc1 as the link-local, but after reboot it
> > > > started
> > > > using
> > > > blahblah:dcc2.
> > > 
> > > Currently, NetworkManager doesn't cope well with changes like
> > > this and
> > > unfortunately this applies to the Git version of NM as well. I
> > > hope
> > > to improve this at some point of time but even the kernel is not
> > > very
> > > helpful here.
> > 
> > Note that IPv6 autoconf would've handled this absolutely
> > gracefully, if
> > NM had not interfered - the box would've expired the default, and
> > the
> > other RA would become active. The right thing to do here is to let
> > the
> > protocol work as designed.
> 
> Right, we should ensure that NM respects the lifetime of the RA.

I added a comment to cover this. If you have any technical comments
 
> > NM only lacks information if you require that NM track the state of
> > the network stack.

This is absolutely necessary.

> > This might be required for DHCP interfaces, since
> > NM
> > needs to manage the DHCP agent.  But what is the use-case for
> > autoconf?

RDNSS and DNSSL are a big enough usecase. Default gateway selection is
another.

> > If someone desires different behavior, then the right thing to do
> > is
> > disable autoconf and use a different interface configuration method
> > (DHCP, static config, etc).

RA configures default gateway. RA configures device routes. RA and DHCP
can be used to configure addresses. RA and DHCP can configure DNS.

It is better to distinguish RA from DHCP as 'addrconf' conveys probably
different meaning to different people.