I think it's easy to see the disagreement just comparing the responses
from Ole and James.

Ole says: 
> I don't see the point of doing address resolution on links without
> addresses.

James says:
> IPV6CP (RFC 2472) negotiates 
> only interface identifiers, and not addresses, and ND
> (2461) says that Neighbor Discovery is supposed to be implemented for
> point-to-point links, so I'd expect ND to be used on those links.

To answer "what's the possible interoperability issue", Markus Jork
nailed it in the referenced thread:
> If one implementation sends a NS and
> expects to see a NA before sending the first message to the neighbors
> address but the other implementation doesn't use NS/NA messages on the
> PPP link, there is a problem.

We have now observed the problem Markus predicted, with real
implementations.
That is, I know of two non-interoperable implementations of RFC 2472.

I think James' argument does have real substance.  The quote from 2461
section 3.2 is (especially the last sentence):

>     point-to-point - Neighbor Discovery handles such links just like
>                      multicast links.  (Multicast can be trivially
>                      provided on point to point links, and interfaces
>                      can be assigned link-local addresses.)  Neighbor
>                      Discovery should be implemented as described in
>                      this document.

If this is the behavior we agree on, then I think that answers my
question.

-Dave

> -----Original Message-----
> From: Ole Troan [mailto:[EMAIL PROTECTED]
> Sent: Tuesday, July 17, 2007 10:49 AM
> To: Dave Thaler
> Cc: [EMAIL PROTECTED]; [email protected]
> Subject: Re: Neighbor Discovery and PPP links
> 
> > Came across this thread...
> >
> > http://www1.ietf.org/mail-archive/web/ipv6/current/msg02314.html
> >
> >
> >
> > However, in looking at draft-ietf-ipv6-over-ppp-v2-03, it seems that
> > this issue was never addressed.
> >
> >
> >
> > Is this intentional?  Was there ever an agreement that ND should or
> > should not be done on PPP links?
> 
> by "ND" you mean address resolution?  I presume there is no
disagreement
> that other ND functions (DAD,NUD,Router Discovery, Prefix Discovery,
> etc) should be done on PPP links.
> 
> > (If there was, I haven't found it yet, only uncertainty and the fact
> > that the IPv6 over PPP RFC has
> >
> > Interoperability problems and that it should be fixed in
> > draft-ietf-ipv6-over-ppp-v2.)
> 
> I don't see the point of doing address resolution on links without
> addresses. 2461 seems quite good at specifying that the LLA options
> should only be included for links with addresses. what's the possible
> interoperabbility issue?
> 
> cheers,
> Ole


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