Internet Engineering Task Force (IETF) S. Chakrabarti
Request for Comments: 8066
Updates: 4944, 6282 G. Montenegro
Category: Standards Track Microsoft
ISSN: 2070-1721 R. Droms
J. Woodyatt
Google
February 2017
IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN)
ESC Dispatch Code Points and Guidelines
Abstract
RFC 4944 defines the ESC dispatch type to allow additional dispatch
octets in the 6LoWPAN header. The value of the ESC dispatch type was
updated by RFC 6282; however, its usage was not defined in either RFC
6282 or RFC 4944. This document updates RFC 4944 and RFC 6282 by
defining the ESC extension octet code points and listing registration
entries for known use cases at the time of writing of this document.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc8066.
Chakrabarti, et al. Standards Track [Page 1]RFC 8066 6LoWPAN ESC Dispatch Code Points February 2017
Copyright Notice
Copyright (c) 2017 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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Usage of ESC Dispatch Octets . . . . . . . . . . . . . . . . 3
3.1. Interaction with Other RFC 4944 Implementations . . . . . 4
3.2. ESC Extension Octets Typical Sequence . . . . . . . . . . 5
3.3. ITU-T G.9903 ESC Type Usage . . . . . . . . . . . . . . . 6
3.4. NALP and ESC Dispatch Types . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Normative References . . . . . . . . . . . . . . . . . . 7
6.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
Chakrabarti, et al. Standards Track [Page 2]RFC 8066 6LoWPAN ESC Dispatch Code Points February 2017
1. Introduction
Section 5.1 of [RFC4944] defines the dispatch header and types. The
ESC type is defined to use additional dispatch octets in the 6LoWPAN
header. RFC 6282 modifies the value of the ESC dispatch type and
that value is recorded in IANA registry [IANA-6LoWPAN]. However, the
octets and usage following the ESC dispatch type are not defined in
either [RFC4944] or [RFC6282]. In recent years with 6LoWPAN
deployments, implementations and standards organizations have started
using the ESC extension octets. This highlights the need for an
updated IANA registration policy.
This document defines the new "ESC Extension Types" registry and the
ESC extension octets for future applications. In addition, this
document records the ITU-T specification for ESC dispatch octet code
points as an existing known usage.
2. Terminology
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 [RFC2119].
3. Usage of ESC Dispatch Octets
RFC 4944 [RFC4944] first introduces this "ESC" dispatch header type
for extension of dispatch octets. RFC 6282 [RFC6282] subsequently
modified its value to [01 000000].
This document specifies that the first octet following the ESC
dispatch type be used for extension type (extended dispatch values).
Subsequent octets are left unstructured for the specific use of the
extension type:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ESC | ESC EXT Type | Extended Dispatch Payload
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Frame Format with ESC Dispatch Type
ESC: The left-most octet is the ESC dispatch type containing
'01000000'.
ESC Extension Type (EET): It is the first octet following the ESC
dispatch type. Extension type defines the payload for the additional
dispatch octets. The values are from 0 to 255. Values 0 and 255 are
reserved for future use. The remaining values from 1 to 254 are
Chakrabarti, et al. Standards Track [Page 3]RFC 8066 6LoWPAN ESC Dispatch Code Points February 2017
assigned by IANA. The EET values are similar to dispatch values in
the 6LoWPAN header except they are preceded by the ESC dispatch type.
Thus, ESC extension types and dispatch values are using orthogonal
code spaces. Though not desirable, multiple ESC dispatch types MAY
appear in a 6LoWPAN header. Section 3.1 describes how to handle an
unknown ESC dispatch type.
Extended Dispatch Payload (EDP): This part of the frame format must
be defined by the corresponding extension type. A specification is
required to define the usage of each extension type and its
corresponding Extension Payload. For the sake of interoperability,
specifications of extension octets MUST NOT redefine the existing ESC
Extension Type codes.
Section 5.1 of RFC 4944 indicates that the Extension Type field may
contain additional dispatch values larger than 63, as corrected by
[Err4359]. For the sake of interoperability, the new dispatch type
(EET) MUST NOT modify the behavior of existing dispatch types
[RFC4944].
3.1. Interaction with Other RFC 4944 Implementations
It is expected that existing implementations of RFC 4944 are not
capable of processing ESC extension data octets as defined in this
document. However, implementers have to assume that an existing
implementation that attempts to process an EET that is unknown to
them will simply drop the packet or ignore the ESC dispatch octets.
If an implementation following this document, during processing of
the received packet, reaches an ESC dispatch type for which it does
not understand the ESC Extension Type (EET) octets, it MUST drop that
packet. However, it is important to clarify that a router node
SHOULD forward a 6LoWPAN packet with the EET octets as long as it
does not attempt to process any unknown ESC extension octets.
Multiple ESC extension octets may appear in a packet. The ESC
dispatch types can appear as the first, last, or middle dispatch
octets. However, a packet will get dropped by any node that does not
understand the EET at the beginning of the packet. Placing an EET
toward the front of the packet has a greater probability of causing
the packet to be dropped than placing the same EET later in the
packet. Placement of an EET later in the packet increases the chance
that a legacy device will recognize and successfully process some
dispatch type [RFC4944] before the EET. In this case, the legacy
device will ignore the EET instead of dropping the entire packet.
Chakrabarti, et al. Standards Track [Page 4]
RFC 8066 6LoWPAN ESC Dispatch Code Points February 2017
3.2. ESC Extension Octets Typical Sequence
The sequence and order of ESC extension octets with respect to the
6LoWPAN Mesh header and LOWPAN_IPHC header are described below. When
the LOWPAN_IPHC dispatch type is present, ESC dispatch types MUST
appear before the LOWPAN_IPHC dispatch type in order to maintain
backward compatibility with Section 3.2 of RFC 6282. The following
diagrams provide examples of ESC extension octet usages:
A LoWPAN encapsulated IPv6 Header compressed packet:
+-------+------+--------+--------+-----------------+--------+
| ESC | EET | EDP |Dispatch| LOWPAN_IPHC hdr | Payld |
+-------+------+--------+--------+-----------------+--------+
A LoWPAN_IPHC Header, Mesh header and an ESC extension octet:
+-----+-----+-----+----+------+-------+---------------+------+
|M typ| Mhdr| ESC | EET|EDP |Disptch|LOWPAN_IPHC hdr| Payld|
+-----+-----+-----+----+------+-------+---------------+------+
A Mesh header with ESC dispatch types:
+-------+-------+-----+-----+-------+
| M Typ | M Hdr | ESC | EET |EDP |
+-------+-------+-----+-----+-------+
With Fragment header:
+-------+-------+--------+------+-----+-----+-------+
| M Typ | M Hdr | F Typ | F hdr|ESC | EET | EDP |
+-------+-------+--------+------+-----+-----+-------+
ESC dispatch type as a LowPAN encapsulation:
+--------+--------+--------+
| ESC | EET | EDP |
+--------+--------+--------+
Figure 2: A 6LoWPAN Packet with ESC Dispatch Types
Chakrabarti, et al. Standards Track [Page 5]RFC 8066 6LoWPAN ESC Dispatch Code Points February 2017
3.3. ITU-T G.9903 ESC Type Usage
The ESC dispatch type is used in [G3-PLC] to provide native mesh
routing and bootstrapping functionalities. The ITU-T recommendation
[G3-PLC] (see Section 9.4.2.3) defines commands that are formatted
like ESC Extension Type fields. The command ID values are 0x01 to
0x1F.
The frame format is defined as follows:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 1| ESC | Command ID | Command Payload
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: G.9903 Frame Format with ESC Dispatch Type
3.4. NALP and ESC Dispatch Types
According to Section 5.1 of RFC 4944 [RFC4944], NALP dispatch octets
are reserved for use as a kind of escape code for identification of
non-6LoWPAN payloads. Since ESC dispatch types are part of 6LoWPAN
dispatch types (extended), they are orthogonal to NALP octets.
This document clarifies that NALP dispatch codes only provide an
escape method for non-6LoWPAN payloads when they appear as the
initial octet of a LoWPAN encapsulation, and that the potential
meaning of their appearance in any other location is reserved for
future use.
4. IANA Considerations
IANA has registered the 'ESC Extension Types' values per the policy
'Specification Required' [RFC5226], following the same policy as in
the IANA Considerations section of [RFC4944]. For each Extension
Type (except the Reserved values), the specification MUST define
corresponding Extended Dispatch Payload frame octets for the receiver
implementation to read the ESC dispatch types in an interoperable
fashion.
Section 4.1 of [RFC5226] indicates that "Specification Required"
calls for a Designated Expert review of the public specification
requesting registration of the ESC Extension Type values.
The allocation of code points should follow the guidelines on "Usage
of ESC Dispatch Octets" (Section 3) and the typical example
(Section 3.2) sections. ESC Extension Type code points MUST be used
in conjunction with 6lo protocols following [RFC4944] or its
Chakrabarti, et al. Standards Track [Page 6]RFC 8066 6LoWPAN ESC Dispatch Code Points February 2017
derivatives. The requesting document MUST specify how the ESC
dispatch octets will be used along with 6LoWPAN headers in their use
cases.
The initial values for the 'ESC Extension Type' fields are as
follows:
+-------+---------------------------------+---------------+
| Value | Description | Reference |
+-------+---------------------------------+---------------+
| 0 | Reserved | This document |
| | | |
| 1-31 | Used by ITU-T G.9903 and G.9905 | ITU-T G.9903 &|
| | Command IDs | ITU-T G.9905 |
| | | |
| 32-254| Unassigned | |
| | | |
| 255 | Reserved | This document |
+-------+---------------------------------+---------------+
Figure 4: Initial Values for the ESC Extension Types Registry
5. Security Considerations
There are no additional security threats due to the assignments of
ESC dispatch type usage described in this document. Furthermore,
this document forbids defining any extended dispatch values or
extension types that modify the behavior of existing dispatch types.
6. References
6.1. Normative References
[Err4359] RFC Errata, Erratum ID 4359, RFC 4944,
<https://www.rfc-editor.org/errata_search.php?eid=4359>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<http://www.rfc-editor.org/info/rfc4944>.
Chakrabarti, et al. Standards Track [Page 7]RFC 8066 6LoWPAN ESC Dispatch Code Points February 2017
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<http://www.rfc-editor.org/info/rfc6282>.
6.2. Informative References
[G3-PLC] International Telecommunications Union, "G.9903 :
Narrowband orthogonal frequency division multiplexing
power line communication transceivers for G3-PLC
networks", February 2014,
<http://www.itu.int/rec/T-REC-G.9903-201402-I>.
[IANA-6LoWPAN]
IANA, "IPv6 Low Power Personal Area Network Parameters",
<https://www.iana.org/assignments/_6lowpan-parameters>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
Acknowledgements
The authors would like to thank the members of the 6lo WG for their
comments. Many thanks to Carsten Bormann, Ralph Droms, Thierry Lys,
Cedric Lavenu, and Pascal Thubert for discussions regarding the bits
allocation issues, which led to this document. Jonathan Hui and
Robert Cragie provided extensive reviews and guidance for
interoperability. The authors acknowledge the comments from the
following people that helped shape this document: Paul Duffy, Don
Sturek, Michael Richardson, Xavier Vilajosana, Scott Mansfield, Dale
Worley, and Russ Housley. Thanks to Brian Haberman, our document
shepherd, for guidance in the IANA Considerations section.
Chakrabarti, et al. Standards Track [Page 8]RFC 8066 6LoWPAN ESC Dispatch Code Points February 2017
Authors' Addresses
Samita Chakrabarti
San Jose, CA
United States of America
Email: samitac.ietf@gmail.com
Gabriel Montenegro
Microsoft
United States of America
Email: gabriel.montenegro@microsoft.com
Ralph Droms
United States of America
Email: rdroms.ietf@gmail.com
James Woodyatt
Google
Mountain View, CA
United States of America
Email: jhw@google.com
Chakrabarti, et al. Standards Track [Page 9]
