Re: Fwd: Re: note from the iesg plenary

["Brian Haberman" <haberman@nortelnetworks.com>]

Erik,

Erik Nordmark wrote:
> 
> > So, I am partly at fault for not getting that text into the architecture
> > draft.  My working definition for a convex site is that for any two
> > points within the site, the shortest path between the points never
> > leaves the site.
> 
> Brian,
> 
> I can see odd cases where using global addresses the traffic would
> indeed leave the site, whereas using site-local address it might not.
> So shouldn't the definition be related to the addresses used?

Correct, it should be in terms of the scope of the addresses being
used.

> 
> Or is there a concern related to a global destination (routed on
> a path that goes outside) and a site-local source, which would cause the
> packet to be dropped at the border?

I know that this subject has been discussed several times.  I believe
the scenario that Margaret is concerned about is based on this
diagram she posted to IPNG several months ago (correct me if I am
wrong, Margaret):

==========================================================
 SITEA
             Host1                      Host2
               |                         |
       ______._|_________    ___.______._|_____________
       Link1 |                  |      |       Link2
             |                (down)   | 
             |                  |      |
             |+-----------------+      |
             ||                        |
============R1========================R3===================
 SITEB       |                         |
             |                         |
        _____|_________________________|________________
                                                 Link3


===========================================================

If Host1 is using site-locals, then Host2 can't be reached and R1
cannot return any info that is very useful to Host1 other than a
Destination Unreachable message.  If Host1 uses a global destination
address and a site-local source address, R1 returns a Scope
Exceeded message even though Host2 is in the same site as Host1.

Brian