Subject: Re: IPv6 autoconfig for a multi-interface host
To: None <>
From: Ignatios Souvatzis <>
List: tech-net
Date: 01/08/2005 14:26:01
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Fri, Jan 07, 2005 at 10:51:42PM -0500, William Allen Simpson wrote:
> Bill Studenmund wrote:
> >Well, not being able to use some form of autoconfig is lame. Think about=
> >all the motherboards with two ethernet interfaces. Hook them both up to=
> >two nets, and v4 works.

Bill St., are you sure? When you use "rdisc" on both interfaces? See below.

> >If v6 can't work in the same way, v6 is less=20
> >useful than v4. :-(

> When I originally designed IPv6 Neighbor Discovery, it was explicitly
> able to autoconfigure on multiple interfaces as a design requirement,
> and in the original code I wrote.

I'm not so sure _Neighbour_ Discovery as such is broken; but I expect
that the router discovery on top of it is broken, and can't be unbroken,
unless we have a way to handle multiple default routes in NetBSD.

Last I looked, we only can have one of them per address family.

Maybe a NetBSD autohost can have address A in network a on interface ia0
and address B on network b, interface ib0, and even chose the right source
addresses for each of them, but what about off-link addresses? It needs to
decide whether to use router-of(a) or router-of(b). Same problem as for
IPv4, only that there you normally either use static configuration or DHCP,
and hopefully the dhcpd(a) and dhcpd(b) are coordinated in a way that your=
multiple-interface host gets one working default router.

Using routed in router-discovery-only mode for IPv4 would have the same
sort of ambiguity, and our documentation advises that no_rdisc might be
needed in that case.

(Actually, I think IPv6 autoconfiguration should be fine for multihomed
hosts if different router lifetime fields (e.g., all but one zero) would
allow selection of the "best" router by our code, but I don't know if our
code does this.)

I'm not familiar with DHCPv6, so can't tell whether it (will) allow(s)=20
to handle this situation better.

seal your e-mail:

Content-Type: application/pgp-signature
Content-Disposition: inline

Version: GnuPG v1.2.3 (NetBSD)