From: Carsten Bormann <[email protected]>
Date: Tue, 9 Jun 2009 20:35:55 +0200
> In particular, I think that it would be
> unfortunate if forwarding messages between two LoWPANs
> required that any router doing such forwarding have a
> whiteboard. Is this the case?
Right now, the architecture is that packets only enter
and leave a LoWPAN through an ER. ERs have whiteboards
and (if multiple) are interconnected by a fast backbone
link.
Can you give more details of a scenario where this is
suboptimal?
One example is wanting to connect an existing ad-hoc LoWPAN
to an IPv6 infrastructure via another LoWPAN. It would be
preferable to do so without moving the existing ad-hoc
whiteboard or adding otherwise unecessary relays.
More generally, I am concerned that requiring a whiteboard
adds a single point of failure and requires having a device
with additional resources. I admit that I am unclear on
exactly how much RAM etc. the whiteboard requires. In
particular, this is why I was asking about the need for
nonvolatile storage.
> Would it be possible to avoid the need for a whiteboard in a
> network by only using IPv6 addresses derived from EUI64s?
> While conflicts are still possible, they are very unlikely
> (outside of development and testing, where they can happen
> with some regularity).
I've got one word for you: counterfeiting.
I'm sorry, I don't follow you. What kind of counterfeiting
does the whiteboard detect? I would think that would
require security mechanisms beyond those mentioned in the ND
draft, e.g. certificates of some kind.
> 802.15.4 16-bit addresses could
> still be used for link-layer next-hop addresses, as that
> requires only local, and not global, conflict detection.
How does local conflict detection work when nodes tend to
attach to routers they haven't seen before?
If the link-layer security makes use of the sender's
EUI64 there has to be some exchange of EUI64's before
messages can be decrypted or authenticated. That
exchange can also detect local conflicts in 16-bit
addresses.
(Such an approach would cost some header compression efficiency, at
about 8 bytes per message.)
Yes.
-Richard Kelsey
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