(usagi-users 03428) Re: Source address for neighbor solicitations

["Peder Chr. Norgaard" <Peder.Chr.Norgaard@xxxxxxxxxxxx>]

On Wed, 22 Jun 2005, Ignacy Gawedzki wrote:

> Hi,
>
> I've just solved a nasty routing problem that came from the fact that routers
> had no link-local address.  It happens that NS initiated by routers are sent
> with the link-local source address (in case the router is not the source of
> the packet that prompted the NS) or are not sent at all if the interface has
> no associated link-local address.
>
> I know that routers MUST have a link-local address on each interface, but
> in case a router doesn't, shouldn't it use any global address available to
> send the NS instead of just silently failing?

I don't think I really understand the context of your question.  (I assume
you are talking IPv6, yes?).  What are the "routers" that you are writing
about?  It cannot be linux 2.6.something kernels - they certainly have
link-local addresses on all IPv6 interfaces.

There is no such case in IPv6 that allows a router (or a host) to not have
a link-local address on any IPv6-capable interface.  If the router hasn't
a link-local address is simply isn't IPv6, so it is quite irrelevant to
ask "in a case a router doesn't".  In that case, you really should return
the router to the vendor, require refund of your payment and don't worry
any more.

(practically, IPv6 routers are using their link-local addresses heavily in
OSPFv3, so an IPv6 router with no link-local addresses wouldn't be able to
run OSPFv3.....)

On the basic level, the RFCs are truly a bit vague on the topic of source
addresses in Neigbor Solicitations from a router, when the NSs are
triggered by forwarding packages.  The RFCs really don't say what to use -
but my general understanding of IPv6 tells me that that the link-local
address is right thing to use in this case.  Mainly because it should
work, and, in the forwarding situation, there really is no mechanism to
choose between any of the potentially several globally routable addresses
assigned to an egress interface.

best regards
--
Peder Chr. Nørgaard        	Senior System Developer, M. Sc.
Ericsson Denmark A/S, Telebit Division
Skanderborgvej 232         	tel: +45 30 91 84 31
DK-8260 Viby J, Denmark         fax: +45 89 38 51 01
        e-mail: Peder.Chr.Norgaard@xxxxxxxxxxxx
(old e-mail 2000-2003: Peder.C.Norgaard@xxxxxxxxxxxxxxx)
         (old e-mail 1992-2000: pcn@xxxxxxx)