Hi Carsten,
On Jun 12, 2009, at 8:16 AM, Carsten Bormann wrote:
Apart from the philosophical argument made by Pascal, there is a big
difference in complexity between 6LoWPAN-ND's NR and DHCP.
Your semantics point ("stateless"):
SAA needs DAD. 6LoWPAN-ND does DAD in a different way, because it
cannot rely on transitive multicast. But it still does SAA.
If you really want to focus on the "stateless" in SAA, what about
the states that an SAA node is in (optimistic, tentative, preferred,
deprecated). I can already argue that original SAA is not
"stateless" for this definition of stateless. So I'm not surprised
you can do that for your favorite definition.
Sorry, replace "state" with "per-node state not maintained by the node
configuring its interface". That is what I meant by "state" in
previous emails and that is what is meant by "state"-less in RFC 4682,
at least my interpretation of it.
The 16-bit address search (it's not really assignment) goes beyond
SAA, yes.
It appears to be a good optimization (and that's what 6LoWPAN-ND is
about) to not let the node guess repeatedly until it finds a free
slot.
I don't see an additional server, the ER is needed in any case.
As I mentioned before, "server" is in the functional sense. It is
additional code running somewhere else other than the node trying to
configure an address. It is a piece of code that a joining node must
interact with simply to join the network. As I said before, if that
server fails, communication to that server fails, or management of
that state fails, nodes cannot properly join the network.
The ER better knows which nodes are in the LoWPAN (or it will create
lots of pointless RREQs), so it is absolutely natural for it to have
that table ("whiteboard").
Again, we all understand the purpose of the whiteboard. I just want to
be fair on what it actually provides and the constraints it places on
the network. In particular, it does not allow a node to perform DAD
autonomously, and as a result, does not allow a node to assign a
preferred address autonomously. OTOH, SLAAC with DAD in RFC 4862 does
allow a node to assign a preferred address autonomously.
--
Jonathan Hui
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