Hi Peter and Colin
> To send the packet without passing via the 6LBR, the source needs the
Link address of the destination, but this link address is only available
to the 6LBR.
I do not see where this conclusion came from?
Provided that the mesh-under solution can derive the (short) link-layer
address from the IP address, I see no particular reason why a node
cannot reach other nodes
in the same subnet via routable addresses? (Yes, this somewhat rules out
DHCP but works nicely along the lines of the -HC draft.
If -ND seems to say otherwise, I suppose this just has to be clarified?
- Anders
________________________________
From: [email protected] [mailto:[email protected]]
On Behalf Of Colin O'Flynn
Sent: Thursday, March 03, 2011 19:35
To: 'Stok, Peter van der'; '6lowpan 6lowpan'
Subject: Re: [6lowpan] nd-15 for isolated network
Hi Peter,
As a disclaimer: I'm not an author of the document, they would
probably be better to give a more complete answer.
I believe your conclusions are entirely correct, as I had
reached the same myself. Basically for mesh-under you are limited to
using the link-local addresses based on EUI-64, as otherwise a 6LN
cannot perform address resolution on another 6LN.
Regards,
-Colin O'Flynn
From: Stok, Peter van der
[mailto:[email protected]]
Sent: March 3, 2011 2:26 PM
To: Colin O'Flynn; '6lowpan 6lowpan'
Subject: RE: [6lowpan] nd-15 for isolated network
Hi Colin,
Thanks for the clarifications.
Sending packets to destinations using mesh-under still remains a
bit vague to me.
Given a LOWPAN with a 6LBR connected to DHCP, DNS, etc, nodes
will use the prefix of the LOWPAN in the IP address.
According to 5.6 a packet with a non link-local IP address is
assumed to be off-link and sent to 6LBR.
However, when the prefix of the destination is the same as the
prefix of the source, source and destination are hosts in the same
LOWPAN. In this case the packet can be sent over the link with
mesh-under routing to the destination.
In my view sending the packet to 6LBR contradicts the mesh-under
concept, because the packet is first routed to 6LBR.
To send the packet without passing via the 6LBR, the source
needs the Link address of the destination, but this link address is only
available to the 6LBR.
A solution is configuring every host as a 6LR, but that defeats
the purpose of the 6LR.
What have I missed?
If the above reasoning is correct, a mechanism is lacking in
which a host can ask the 6LBR the link address of a given IP address
with the LOWPAN prefix to allow proper mesh-under routing.
Looking forward to your reaction.
Peter
From: Colin O'Flynn [mailto:[email protected]]
Sent: Tuesday 1 March 2011 14:03
To: Stok, Peter van der; '6lowpan 6lowpan'
Subject: RE: [6lowpan] nd-15 for isolated network
Hi Peter,
I think you are basically correct, with some additional
constraints or clarifications:
The 6LN NC will have entries for routers it has registered with,
so it's not always empty.
Section 5.6 allows you to use the MAC extraction only if the
link-local address is EUI-64 based. This basically means if the U/L bit
is set, indicating the address in question was generated from a
known-unique MAC address. 802.15.4 for example has 16-bit addresses you
could be using instead.
I think most networks would have the 6LBR, although obviously if
you have a very specific situation as you outlined you could skip it.
The 6LBR at minimum would manage the compression context (if required)
and serve as an alternative way to reach a node by a default route. From
a maintenance/deployment/management perspective the 6LBR is an easy way
to see what nodes are alive on your network too by checking its tables.
Regards,
-Colin
From: [email protected] [mailto:[email protected]]
On Behalf Of Stok, Peter van der
Sent: March 1, 2011 1:21 PM
To: 6lowpan 6lowpan
Subject: [6lowpan] nd-15 for isolated network
Dear authors,
The document looks rather complete and comprehensive.
There are a few questions:
Do I understand correctly that contrary to RFC 4861, the
neighbor cache is always empty in 6LN. If true, this remark may be added
to Registration term of section 2.
From that do I deduce correctly that access to the link for
link-local addresses (LLA) involves extracting the MAC address from the
LLA.
MUST a 6LBR be present in an isolated LOWPAN? (6LBR text in
section 2 seems to imply this)
Assuming an isolated LOWPAN without 6LR or 6LBR, then there will
be no answer to the RS message, but the node can continue sending
messages to LLA, where the MAC address is again extracted from the LLA.
Is that correct?
Peter
Peter van der Stok
Philips Research Laboratories Eindhoven
High Tech Campus
HTC 34 (WB) 1-067
5656 AA Eindhoven
The Netherlands
phone +31 40 2749657
Fax: + 31 40 2746321
mailto: [email protected]
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