Hi Zach,
On Apr 12, 2009, at 3:42 AM, Zach Shelby wrote:
Specific to the 6LoWPAN ND draft, you do bring up an important case
- one where two or more Edge Routers are not connected by a
"backbone" network. I think there are interesting questions there
that are not dealt with in the current 6LoWPAN ND draft (e.g. how
is the whiteboard information distributed between edge routers if
at all? can we have a particular whiteboard specific for a prefix
maintained at only the Edge Router that advertises that prefix? do
whiteboards have to be maintained at edge routers?). We should
probably open a new thread on this topic in the 6LoWPAN ML...
The Whiteboard is specific to a LoWPAN (= a prefix). Whiteboard
information is not distributed between different LoWPANs (there is
no point). In an extended LoWPAN multiple whiteboards on ARs are
part of the same LoWPAN (same prefix) and use a backbone link to
perform DAD and claim/defend node addresses across the whole LoWPAN.
Be careful about your definition of a "LoWPAN". Just because a LoWPAN
is defined by a single prefix doesn't mean that a PAN cannot support
multiple prefixes.
In Richard's case, I see two different Access Routers *not* connected
over a backbone but advertise different prefixes to the same PAN.
Nodes in the PAN may be multihomed and configure addresses for the two
different networks. If we define a whiteboard to manage addresses for
a particular prefix, then we have two whiteboards and let's assume
that each resides at their respective advertising Access Router. I
think there's an open question as to how RRs are sent - in particular,
how does an RR get sent to the appropriate whiteboard? This is not
considered in the current ND draft.
A Whiteboard does not need to be located at an AR, but it is a
logical place in most cases. In the Extended LoWPAN case the
whiteboard needs to be located on nodes which have a shared backbone
link (usually ARs).
We discuss that a little in the ND draft but I think it can be
expanded to make that clear with an example.
I do think we need to be more clear. The draft is confusing because it
makes concrete statements like: "The edge router maintains a
whiteboard of all hosts in the network." There's a bunch of
assumptions that can be made from this statement. The obvious is that
the whiteboard is located at an edge router. Another is that the
whiteboard is not bound to a particular prefix, but maintains
information for all hosts.
--
Jonathan Hui
- Zach
--
Jonathan Hui
On Apr 10, 2009, at 1:01 PM, Richard Kelsey wrote:
From: Carsten Bormann <[email protected]>
Date: Fri, 10 Apr 2009 19:00:42 +0200
(I don't tend to think about the case where there is no
Edge Router -- ...)
I have a question on this, stemming from my lack of
familiarity with the details of IP routing.
Suppose I have a 6LowPAN/ROLL network being used for energy
management in a home. The network includes the electric
meter, which has a backhaul connection back to the utility.
The utility, being very protective of its backhaul network,
has a firewall in the meter to keep out everything except
the utility's own traffic. Given the presence of the
firewall, does it still make sense to use the meter as an
Edge Router?
-Richard Kelsey
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http://zachshelby.org - My blog “On the Internet of Things”
Mobile: +358 40 7796297
Zach Shelby
Head of Research
Sensinode Ltd.
Kidekuja 2
88610 Vuokatti, FINLAND
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