Subject: Re: [lisp] Gen-ART IETF Last Call review of draft-ietf-lisp-ddt-08
From: [email-masked] (Dale R. Worley)
To: Dino Farinacci <[email-masked]>
Cc: [email-masked]
Date: Tue, 17 Jan 2017 16:32:50 -0500
List-Id: List for the discussion of the Locator/ID Separation Protocol <lisp.ietf.org>

I reviewed draft-ietf-lisp-ddt-08, and my memory is that the only
significant technical question was regarding the "D" bit in Map-Request
messages.

Thinking back on it, I believe that the difficulty I was having was with
the explanation of the D bit, not its functionality.  In particular, a
DDT server can share a node and a listening port with a Map-Server.
Both of these servers process Map-Request messages, albeit with
different semantics.  Hence the D bit in Map-Request messages is needed
to differentiate which server is to process a given Map-Request message.

My suggestion is that the document define the D bit in this way.  Once
that is done, it's obvious for a particular client sending a particular
message whether the D bit should be set.  Compare with the current
description, which speaks of the D bit as if it is a classification of
the sender of the Map-Request, which leads to conceptual problems
because it requires the document to define the classification and ensure
that all possible clients are properly classified.

(Ideally, I would advocate that a DDT Map-Request should have a
different type code than a Map-Server Map-Request.  But I'm sure that it
is too late to put that fix into existing deployments.)

Dale