Hi Rich,
>Your example also has the best route between H1 & H2 in site B, be to go
>through site A. This seems really unlikely to occur in actual practice. You
>seem to be implicitly assuming that the two sites are in a single IGP
>routing domain.
I am assuming that two sites _may_ be in the same routing domain, and
that problems could occur in that situation. I don't believe that the
current IPv6 specifications assume that a single routing domain will
always be a single site.
My example packet could easily occur in response to a packet sent from
a host that doesn't have a site-local address (perhaps because it was
configured via DHCP?). That host would need to use a global address to
communicate with a site-local address, and the response would have
a site-local source and a global destination.
The ICMP issue that you have described would also exist when using
multiple "conceptual" routing tables in the case of a partitioned
site. For example:
==========================================================
SITEA
Host1 Host2
| |
________|__.__._____ ____.______._|_____________
Link1 | | | | Link2
| | (down) |
| +-----R1----+ |
| |
| |
===========|=====================|=========================
SITEB | |
+--------R1-----------+
===========================================================
If a site-local packet (site-local destination and site-
local source) is send from Host1 to Host2, it would
probably be sent to the local router, R1.
R1 would then use the scoped addressing rules to forward the
packet. First, he would look at the destination address
to determine that he should look in the site-local table.
The site-local table would have no active route to Link2,
so he would send a Destination Unreachable/No Route
To Destination message, _not_ a Scope Exceeded message.
In this case, it might actually be _useful_ for the sender
to receive a Scope Exceeded message, because the sender might
be able to switch to global communication. The sender may
have had both site-local and global addresses available, but
have chosen site-local communication. But, he doesn't get the
Scope Exceeded message, so he can't act on it.
However, if a mixed scope packet is sent (global destination
and site-local source) from Host1 to Host2, R1 would look
in the global table, determine that a route exists to Link2
through R2, THEN discard the packet because of the site-local
source. This would result in a Destination Unreachable/Scope
Exceeded message. It seems unlikely, though, that Host1 would
have sent a mixed-scope packet if he had a global address
available for Host2, so the Scope Exceeded message is potentially
_less_ useful in this situation.
Margaret
--------------------------------------------------------------------
IETF IPng Working Group Mailing List
IPng Home Page: http://playground.sun.com/ipng
FTP archive: ftp://playground.sun.com/pub/ipng
Direct all administrative requests to [EMAIL PROTECTED]
--------------------------------------------------------------------
