Subject: [NSIS] Loose-End MRM Direction

From: Christian Dickmann <[email-masked]>
Date: Thu, 3 Aug 2006 12:10:12 +0200

Hi Robert,

I just read the text about Loose-End MRM again and wondered
about the text "D flag: The direction flag. The only valid 
value is D=0 (see Section 5.8.2)."

The NATFW NSLP defines to use LEMRM for some cases of the REA
message. I wonder how the response can travel back to
the initiator if only downstream direction is allowed.
Even a GIST Query/Response would not work, as according to
Section 5.1 of the GIST draft the Response has inverted direction.
"Note that the direction of this MRI will be
 inverted compared to that in the Query, that is, an upstream MRI
 becomes downstream and vice versa (see Section 3.3)."

So I wondered if maybe using LEMRM implicitly means, that
there is no GIST routing-state installed, but the question
remains how to send the response to the REA back to initiator.

Can you please clarify this?

Christian Dickmann

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From: Roland Bless <[email-masked]>
Date: Wed, 09 Aug 2006 14:53:59 +0200

Hi Christian,

> value is D=0 (see Section 5.8.2)."

Good point! We are indeed a little bit confused, too.
The draft also says in sec. 5.8.2.1:
                              Additional control information defines the
   direction of the message relative to this flow as in the path-coupled
   case.

What control information in which protocol? In GIST or in the NSLP?
Or do you mean the D-flag (which is currently pretty useless)?

> the initiator if only downstream direction is allowed.

Actually that could be figured out by checking who actually
sent the message, i.e. upstream or downstream peer. In either
case you must forward it to the other peer. But that would break
implementations that rely on evaluating the D-flag while routing
messages and I think it will be an inconsequent use of the D-flag.
Actually change history says:
23.  Clarified why only D=0 is valid for the loose-end MRM in
        Appendix A.3.1.2 [AD review comment L23].
but frankly I don't see any explanation for this.

> remains how to send the response to the REA back to initiator.

A possibility would be to forward a message to the
upstream peer if it came from the downstream peer
and vice versa. But I'm not sure that this will work
in all cases.

> Can you please clarify this?

We are also looking forward to an answer.

Regards,
 Roland