6lo S. Chakrabarti
Internet-Draft
Updates: 4944, 6282 (if approved) G. Montenegro
Intended status: Standards Track Microsoft
Expires: June 11, 2017 R. Droms
J. Woodyatt
Google
December 8, 2016
6lowpan ESC Dispatch Code Points and Guidelines
draft-ietf-6lo-dispatch-iana-registry-07
Abstract
RFC4944 defines the ESC dispatch type to allow for additional
dispatch octets in the 6lowpan header. The value of the ESC dispatch
type was updated by RFC6282, however, its usage was not defined
either in RFC6282 or in RFC4944. This document updates RFC4944 and
RFC6282 by defining the ESC extension octet code points including
registration of entries for known use cases at the time of writing of
this document.
Status of this Memo
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This Internet-Draft will expire on June 11, 2017.
Copyright Notice
Copyright (c) 2016 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Usage of ESC dispatch octets . . . . . . . . . . . . . . . . . 3
3.1. Interaction with other RFC4944 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. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
[RFC4944] section 5.1 defines the dispatch header and types. The ESC
type is defined for using 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 [6LOWPAN-IANA]. However, the
octets and usage following the ESC dispatch type are not defined in
either [RFC4944] and [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.
The following sections record the ITU-T specification for ESC
dispatch octet code points as an existing known usage and propose the
definition of ESC extension octets for future applications. The
document also requests IANA actions for the first extension octet
following the ESC dispatch type.
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
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'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
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 each usage of 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 in RFC4944 indicates that the Extension Type field may
contain additional dispatch values larger than 63, as corrected by
[4944-ERRATA]. 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 RFC4944 implementations
It is expected that existing implementations of RFC4944 are not
capable of processing ESC extension data octets as defined in this
document. However, implementers have to assume that existing
implementation that attempt to process an EET 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 extension octets (EET), 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
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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.
3.2. ESC Extension Octets Typical Sequence
ESC Extension octets sequence and order with respect to 6LoWPAN Mesh
header and LoWPAN_IPHC header are described below. When LOWPAN_IPHC
dispatch type is present, ESC dispatch types MUST appear before the
LOWPAN_IPHC dispatch type in order to maintain backward compatibility
with RFC6282 section 3.2. 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
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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] section 9.4.2.3 defines commands which 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 RFC4944 [RFC4944] section 5.1, 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
This document requests IANA to register the 'ESC Extension Type'
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.
[RFC5226] section 4.1 also 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
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of ESC dispatch octets" and the typical example sections. ESC
Extension type code points MUST be used in conjunction with 6lo
protocols following [RFC4944] or its 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:
+-------+---------------------------------+---------------+
| Value | Description | Reference |
+-------+---------------------------------+---------------+
| 0 | Reserved for future use | 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 | This document |
| |(Reserved for future IANA | |
| | Assignment-- Spec Required) | |
| | | |
| 255 | Reserved for future use | This document |
+-------+---------------------------------+---------------+
Figure 4: Initial Values for IANA 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. 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, 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.
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This document was produced using the xml2rfc tool.
7. References
7.1. Normative References
[4944-ERRATA]
"https://www.rfc-editor.org/errata_search.php/doc/html/rfc4944".
[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>.
[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>.
7.2. Informative References
[6LOWPAN-IANA]
"https://www.iana.org/assignments/_6lowpan-parameters/
_6lowpan-parameters.xhtml".
[6loCHART]
"https://datatracker.ietf.org/wg/6lo/charter".
[G3-PLC] "http://www.itu.int/rec/T-REC-G.9903-201402-I".
[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>.
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Authors' Addresses
Samita Chakrabarti
San Jose, CA
USA
Email: samitac.ietf@gmail.com
Gabriel Montenegro
Microsoft
USA
Email: gabriel.montenegro@microsoft.com
Ralph Droms
USA
Email: rdroms.ietf@gmail.com
James Woodyatt
Google
Mountain View, CA
USA
Email: jhw@google.com
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