Subject: RE: draft-ipngwg-default-addr-select-00.txt

From: Tim Hartrick <[email-masked]>
Date: Fri, 29 Oct 1999 09:32:52 -0700 (PDT)

Steve,

> 
> At 12:00 AM -0700 10/29/99, Richard Draves wrote:
> >...link-local destinations can't be forwarded between interfaces,...
> 
> Link-locals *can* be forwarded between interfaces connected to the same link.
> 

OK.  I have to ask.  Why would you want to do this.  If the two interfaces
are indeed attached to the same link then presumeably the real destination
interface would already be receiving traffic destined to it.  There would be
no need for the other interface on the same link to forward the traffic to
the real destination interface.

Is there some multicast related reason that this behavior would be desireable
that my feeble mind can't comprehend at the moment?

tim
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From: Steve Deering <[email-masked]>
Date: Fri, 29 Oct 1999 10:06:26 -0700

At 9:32 AM -0700 10/29/99, Tim Hartrick wrote:
>OK.  I have to ask.  Why would you want to do this.

It's not that I "want" to do it, but I think it is a possibility that
falls out of the architecture.  The fact is, it is physically possible
to connect more than one interface to the same link, and the semantics
of link-local addresses do not require that we forbid forwarding of
link-locals from one such interface to another.

>If the two interfaces
>interface would already be receiving traffic destined to it.

That's probably true.  I was imagining (but cannot fully explain) a
scenario in which a link-local packet is sent not to its intended
destination but rather to a router on the link (perhaps because of
out-of-date/invalid address resolution data on the source?), and the
router then sends it back onto the link towards the proper destination,
and also sends a Redirect to the source so it doesn't keep happening.
If the router happened to have multiple interfaces to the link, there
would be no reason to forbid it from sending the data packet back out
a different interface than the one it arrived on.

>that my feeble mind can't comprehend at the moment?

No, I wasn't thinking of any multicast reason.  I'm pretty sure you never
want to send a multicast packet back onto the link it arrived from.

Steve