6LoWPAN Working Group C. Bormann
Internet-Draft Universitaet Bremen TZI
Intended status: Informational March 7, 2011
Expires: September 8, 2011
6LoWPAN Roadmap and Implementation Guide
draft-bormann-6lowpan-roadmap-00
Abstract
6LoWPAN is defined in RFC 4944 in conjunction with a number of
specifications that are currently nearing completion. The entirety
of these specifications may be hard to understand, pose specific
implementation problems, or be simply inconsistent.
The present guide aims to provide a roadmap to these documents as
well as provide specific advice how to use these specifications in
combination. In certain cases, it may provide clarifications or even
corrections to the specifications referenced.
This guide is intended as a continued work-in-progress, i.e. a long-
lived Internet-Draft, to be updated whenever new information becomes
available and new consensus on how to handle issues is formed.
Similar to the ROHC implementation guide, RFC 4815, it might be
published as an RFC at some future time later in the acceptance curve
of the specifications.
This document does not describe a new protocol or attempts to set a
new standard of any kind -- it mostly describes good practice in
using the existing specifications, but it may also document emerging
consensus where a correction needs to be made.
The current version -00 of this document is just an initial draft
that is intended to spark the collection of relevant information.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 8, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. 6LoWPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. 6LoWPAN MTU . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. PAN identifiers in IPv6 addresses . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
(To be written - for now please read the Abstract.)
1.1. Terminology
This document is a guide. However, it might evolve to make specific
recommendations on how to use standards-track specification.
Therefore: The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC
2119. They indicate requirement levels for compliant 6LoWPAN
implementations [RFC2119]. Note that these keywords are not only
used where a correction or clarification is intended; the latter are
explicitly identified as such.
The term "byte" is used in its now customary sense as a synonym for
"octet".
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2. 6LoWPAN
What is a 6LoWPAN?
The term, originally just the name of the IETF WG that created the
specifications, nowadays refers to a specific way of building IP-
connected wireless networks for embedded use cases. The 6LoWPAN core
specifications are:
o [RFC4944], as updated by
o [I-D.ietf-6lowpan-hc] and
o [I-D.ietf-6lowpan-nd].
While [RFC4944] defines 6LoWPAN specifically for IEEE 802.15.4
networks, 6LoWPAN concepts have been applied to other PHY/MAC layers.
6LoWPANs MAY use additional protocols, such as [I-D.ietf-roll-rpl]
for routing, or [I-D.ietf-core-coap] for application data transfer.
However, the "6LoWPANness" of a network is caused by adherence to the
core specifications.
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3. 6LoWPAN MTU
IPv6 defines a minimal value for the "Minimum Transmission Unit",
MTU, of 1280 bytes. This means that every IPv6 network must be able
to transfer a packet of at least 1280 bytes of IPv6 headers and data
without requiring fragmentation.
A common Internet MTU is 1500 bytes (motivated by the Ethernet MTU).
The gap between 1280 and 1500 allows tunneling protocols to insert
headers on the way from the source of a packet to a destination
without breaking the overall MTU of the path. As various tunneling
protocols do indeed insert bytes, it is unwise to simply assume an
end-to-end MTU of 1500 bytes even with the current dominance of
Ethernet. Path MTU discovery [RFC1981] [RFC4821] has been defined to
enable transport protocols to find an MTU value better than 1280
bytes, but still reliably within the MTU of the path being used.
Path MTU discovery places, however, additional strain on constrained
nodes, which therefore may want to stick with an MTU of 1280 bytes
for all IPv6 applications.
6LoWPAN was designed as a stub network, not requiring any tunneling.
As IEEE 802.15.4 packets are rather small (127 bytes maximum at the
physical layer, minus MAC/security and adaptation layer overhead),
1280 bytes was already considered a somewhat large packet size.
Therefore, the 6LoWPAN network MTU was simply set at the minimum size
allowable by IPv6, 1280 bytes, although the 6LoWPAN fragmentation
mechanism is able to support packets with total lengths (including
the initial IPv6 header) of up to 2047 bytes.
As a more recent development, some modes of operation of the RPL
protocol [I-D.ietf-roll-rpl] do indeed operate by tunneling data
packets between RPL routers. Maintaining the MTU visible to
applications at 1280 therefore requires making a larger MTU available
to the tunnels.
6LoWPAN routers that employ RPL therefore MUST support a more
appropriate MTU between routers that make use of tunneling between
them. [The specific MTU value is TBD, to be chosen between 1280 and
2047 based on RPL considerations that need to be added to this
document.]
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4. PAN identifiers in IPv6 addresses
[RFC4944] incorporates PAN identifiers in IPv6 addresses created from
16-bit MAC addresses, in a somewhat awkward way (one of the 16 bits
needs to be cleared to enable the U/L bit.).
As the use of PAN identifiers in 6LoWPAN networks has since become
less and less meaningful, [I-D.ietf-6lowpan-hc] provides specific
support only for interface IDs of the form 0000:00ff:fe00:XXXX, i.e.
PAN identifiers of zero. (Other forms can be supported by creating
sufficiently long pieces of compression context information for each
non-zero PAN identifier; however there is a limited number of context
elements and each consumes space in all nodes of a 6LoWPAN.)
It is therefore RECOMMENDED to employ a PAN identifier of zero with
6LoWPAN.
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5. IANA Considerations
This document has no actions for IANA.
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6. Security Considerations
(None so far; this section will certainly grow as additional security
considerations beyond those listed in the base specifications become
known.)
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7. Acknowledgements
(The concept for this document is borrowed from [RFC4815], which was
invented by Lars-Erik Jonsson. Thanks!)
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8. References
8.1. Normative References
[I-D.ietf-6lowpan-hc]
Hui, J. and P. Thubert, "Compression Format for IPv6
Datagrams in Low Power and Lossy Networks (6LoWPAN)",
draft-ietf-6lowpan-hc-15 (work in progress),
February 2011.
[I-D.ietf-6lowpan-nd]
Shelby, Z., Chakrabarti, S., and E. Nordmark, "Neighbor
Discovery Optimization for Low-power and Lossy Networks",
draft-ietf-6lowpan-nd-15 (work in progress),
December 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, September 2007.
8.2. Informative References
[I-D.ietf-core-coap]
Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
"Constrained Application Protocol (CoAP)",
draft-ietf-core-coap-04 (work in progress), January 2011.
[I-D.ietf-roll-rpl]
Winter, T., Thubert, P., Brandt, A., Clausen, T., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., and J.
Vasseur, "RPL: IPv6 Routing Protocol for Low power and
Lossy Networks", draft-ietf-roll-rpl-18 (work in
progress), February 2011.
[RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
for IP version 6", RFC 1981, August 1996.
[RFC4815] Jonsson, L-E., Sandlund, K., Pelletier, G., and P. Kremer,
"RObust Header Compression (ROHC): Corrections and
Clarifications to RFC 3095", RFC 4815, February 2007.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, March 2007.
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Author's Address
Carsten Bormann
Universitaet Bremen TZI
Postfach 330440
Bremen D-28359
Germany
Phone: +49-421-218-63921
Fax: +49-421-218-7000
Email: cabo@tzi.org
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