[radvd-devel-l] Router advertisement and forwarding on client side?

vincent.trucmuche vincent.trucmuche at laposte.net
Mon Mar 19 11:36:24 EST 2007

Thank you Pekka for you fast answer :)

> Combining the responses..
I would have prefer not combining them as they are linked but
different questions. It would be easier to follow 2 questions
as 2 different threads... but this is not a big deal ;)

> On Mon, 19 Mar 2007, vincent.trucmuche wrote:
> > Why radvd doesn't start if forwarding is disabled?
> >
> >RFC2461 states
> >   "A Lifetime of 0 indicates that the router is not a
> >default router and SHOULD NOT appear on the default
> >router list."
> >
> >It appears that a machine on the link may announce prefixes
> >w/o being a router.
> In most scenarios encountered to date, radvd is useful when
> forwarding packets.  Non-forwarding operation could be
supported if 
> there is sufficient case to be made to do so, and
appropriate code to 
> do so.

I disagree with this ;)
A limitation (preventing radvd to run on a non forwarding
machine) has been introduced w/o any reason (AFAIK). I don't
understand why I should prove this limitation is not useful. I
would think that you (radvd team :) ) should argue why this
limitation is needed. :)
What is the problem if we remove this limitation?

> What are the specific scenarios (e.g., when Lifetime is 0)
where this 
> would be useful?  In particular, what radvd would be
advertising if it 
> should be used to forward packets?  (Note that 'being a default 
> router' is a subset of 'forwarding packets')

Simplest case is:
One want to have a "configuration server" (DHCP & RA),
different from the router.

> > My question is not really a question about radvd but very
> > linked to it. It concern client side into the kernel.
> >
> > Why linux Kernel drop RA packets if in forwarding mode?
> > I saw nothing in RFCs prohibiting a router to configure its
> > interface address or its default route using RA.
> RFC2462 and its successor says at the start of the abstract
> _host_ there):
>     This document specifies the steps a host takes in
deciding how to
>     autoconfigure its interfaces in IP version 6. [...]
> The specifications haven't been designed with a router
> its addresses.  While router configuring an address from the
prefix it 
> advertises (in contrast to configuring address from prefixes
it hears) 
> could be better justified, even this has been frowned on.
RFCs don't look to me so clear. It is stated that "hosts" can
autoconfigure. We could then think that routers can't. But
can't we think that routers can, sometime, be consider as host?

I have a case to submit.
How to configure the default gateway of a CPE? This CPE is a
routeur between WAN and LAN. DHCPv6 is not able to configure
gateway address and RA are discarded. How my CPE will learn
its default gateway? This is typically a case where I would
like my CPE learn its gateway address using RA. :)


Envoyez vos cartes de voeux depuis www.laposte.net 
Elles seront ensuite distribuées par le facteur : pratique et malin !

More information about the radvd-devel-l mailing list