Hi,
Jonathan Hui wrote:
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.
I agree completely. You can have several LoWPANs (L3 concept) running
over the same PAN (L2 concept specific to IEEE 802.15.4).
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.
Yep, this will be a common case. A router will need to specifically
choose which LoWPAN it wants to advertise routes for so it is
advertising a consistent prefix information set of context IDs. This way
a host can choose which LoWPAN to participate in by choosing the router
advertising that prefix. Hosts could then multihome as you suggest. Yes,
we need to discuss that in the draft more. As the draft is now we don't
have sufficient information advertised in RAs to allow routers to
advertise prefixes for multiple LoWPANs simultaneously.
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.
Agreed. Will make a ticket for this.
--
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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Zach Shelby
Head of Research
Sensinode Ltd.
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88610 Vuokatti, FINLAND
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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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