Subject: RE: 2461bis update

From: "Soliman, Hesham" <[email-masked]>
Date: Wed, 1 Jun 2005 12:16:10 -0400

> I have one issue with APPENDIX A.  The direct mention of the on-link
 > assumption was removed from the appendix (from the second bullet item
 > 1), but it is still implied by the text that remains.  The text is:
 > 
 >      1) If no Router Advertisement is received on any interfaces, a
 >         multihomed host will have no way of knowing which 
 > interface to
 >         send packets out on, even for on-link destinations.
 >         One possible approach for a multihomed node would be 
 > to attempt
 >         to perform address resolution on all interfaces, a step
 >         involving significant complexity.
 > 
 > Why would a multihomed host ever attempt to perform any address
 > resolution on any interface unless it assumed that the 
 > destination was
 > on-link on one of those interfaces?  It should not make this 
 > assumption
 > at all.  While the text is accurate in stating that this involves
 > significant complexity, it should not suggest that doing 
 > on-link address
 > resolution for a node to which it has no route is a "possible
 > approach".  If you're multihomed and you have no route to a 
 > destination,
 > then send back an ICMP destination unreachable.  It should 
 > be as simple
 > as that.

=> How do you know if you have no route to the destination?
Could it not be on one of the links? The difference is that
this case does not _assume_ that the destination is on-link, which
was there before. 

In any case, this issue was discussed with Jinmei last week and 
here is the suggested text that we agreed on. Please let me know
if you have a comment:

>> 1) If no Router Advertisement is received on any interfaces, a
>> multihomed host will have no way of knowing which 
>> interface to
>> send packets out on, even for on-link destinations.  One
>> possible approach for a multihomed node would be to 
>> attempt to
>> perform address resolution on all interfaces.  The same
>> argument applies to a singlehomed node that does not receive
>> any Router Advertisement, but the step in the multihomed case
>> involves significant complexity.

Hesham

===========================================================
This email may contain confidential and privileged material for the sole use
 of the intended recipient.  Any review or distribution by others is strictly
 prohibited.  If you are not the intended recipient please contact the sender
 and delete all copies.
===========================================================

--------------------------------------------------------------------
IETF IPv6 working group mailing list
[email-masked]
Administrative Requests: https://www1.ietf.org/mailman/listinfo/ipv6
--------------------------------------------------------------------

---

From: Sebastien Roy <[email-masked]>
Date: Wed, 01 Jun 2005 12:57:48 -0400

> => How do you know if you have no route to the destination?

You consult your forwarding table.

> Could it not be on one of the links?

It could be if you have a forwarding table entry that points to one or
more of your local interfaces.

>  The difference is that

I does assume that that the destination is on-link.  In outbound packet
processing, you don't attempt to do link-layer address resolution until
you've done the forwarding table lookup and done on-link determination.

> >> involves significant complexity.

The same argument does not apply to single homed nodes.  The point of
removing the on-link assumption was to make sure the node does _not_ do
address resolution in the absence of a route to the destination.  Are
you saying that it's ok to do that if you have more than one network
interface?  That's how I read this text.

-Seb

---

From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Thu, 02 Jun 2005 02:59:32 +0900

>>>>> On Wed, 01 Jun 2005 12:57:48 -0400, 
>>>>> Sebastien Roy <[email-masked]> said:

> interface?  That's how I read this text.

If you've not read the discussion last week, please check the
following links:

http://www1.ietf.org/mail-archive/web/ipv6/current/msg05047.html
http://www1.ietf.org/mail-archive/web/ipv6/current/msg05050.html
http://www1.ietf.org/mail-archive/web/ipv6/current/msg05053.html
http://www1.ietf.org/mail-archive/web/ipv6/current/msg05057.html
http://www1.ietf.org/mail-archive/web/ipv6/current/msg05058.html

In summary, I believe I stand at the same position as yours.  My
understanding of the current wording in the 03 draft is that it
strangely talks about a "multihome version of on-link assumption".
While I was not convinced with Hesham's response that "this is
actually not the on-link assumption since this is just 'attempt', not
a 'requirement'", I suggested the above text in case we really still
want to emphasize the complexity specific to the multihomed case.  As
I stated in msg05058.html, my primary preference is to remove this
part altogether with the removal of the on-link assumption.

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					[email-masked]