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Droms 8 J. Woodyatt 9 Nest 10 November 16, 2016 12 6lowpan ESC Dispatch Code Points and Guidelines 13 draft-ietf-6lo-dispatch-iana-registry-06 15 Abstract 17 RFC4944 defines the ESC dispatch type to allow for additional 18 dispatch bytes in the 6lowpan header. The value of the ESC byte was 19 updated by RFC6282, however, its usage was not defined either in 20 RFC6282 or in RFC4944. This document updates RFC4944 and RFC6282 by 21 defining the ESC extension byte code points including registration of 22 entries for known use cases at the time of writing of this document. 24 Status of this Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at http://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on May 20, 2017. 41 Copyright Notice 43 Copyright (c) 2016 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 60 3. Usage of ESC dispatch bytes . . . . . . . . . . . . . . . . . . 3 61 3.1. Interaction with other RFC4944 implementations . . . . . . 4 62 3.2. ESC Extension Bytes Typical Sequence . . . . . . . . . . . 5 63 3.3. ITU-T G.9903 ESC type usage . . . . . . . . . . . . . . . 5 64 3.4. NALP and ESC bytes . . . . . . . . . . . . . . . . . . . . 6 65 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 66 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 67 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 68 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 69 7.1. Normative References . . . . . . . . . . . . . . . . . . . 8 70 7.2. Informative References . . . . . . . . . . . . . . . . . . 8 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 73 1. Introduction 75 [RFC4944] section 5.1 defines the dispatch header and types. The ESC 76 type is defined for using additional dispatch bytes in the 6lowpan 77 header. RFC 6282 modifies the value of the ESC dispatch type and it 78 is recorded in IANA registry [6LOWPAN-IANA]. However, the bytes and 79 usage following the ESC byte are not defined in either [RFC4944] and 80 [RFC6282]. However, in recent years with 6lowpan deployments, 81 implementations and standards organizations have started using the 82 ESC extension bytes and co-ordination between the respective 83 organizations and IETF/IANA is needed. 85 The following sections record the ITU-T specification for ESC 86 dispatch byte code points as an existing known usage and propose the 87 definition of ESC extension bytes for future applications. The 88 document also requests IANA actions for the first extension byte 89 following the ESC byte. 91 2. Terminology 93 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 94 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 95 document are to be interpreted as described in [RFC2119]. 97 3. Usage of ESC dispatch bytes 99 RFC 4944 [RFC4944] first introduces this "ESC" dispatch header type 100 for extension of dispatch bytes. RFC 6282 [RFC6282] subsequently 101 modified its value to [01 000000]. 103 This document specifies that the first octet following the ESC byte 104 be used for extension type (extended dispatch values). Subsequent 105 octets are left unstructured for the specific use of the extension 106 type: 108 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 1 109 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 110 |0 1| ESC | ESC EXT Type | Extended Dispatch Payload 111 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 113 Figure 1: Frame Format with ESC Byte 115 ESC: The left-most byte is the ESC dispatch type containing 116 '01000000' 118 ESC Extension Type (EET): It is the first byte following the ESC 119 byte. Extension type defines the payload for the additional dispatch 120 bytes. The values are from 0 to 255. Values 0 and 255 are reserved 121 for future use. These values are assigned by IANA. The EET values 122 are similar to dispatch values in the 6lowpan header except they are 123 preceded by the ESC byte. Thus, ESC extension types and dispatch 124 values are using orthogonal code spaces. Though not desirable, 125 multiple ESC bytes MAY appear in a 6lowpan header. Section 3.1 126 describes how to handle an unknown ESC dispatch type. 128 Extended Dispatch Payload(EDP): This part of the frame format must be 129 defined by the corresponding extension type. A specification is 130 required to define each usage of extension type and its corresponding 131 Extension Payload. For the sake of interoperability, specifications 132 of extension bytes MUST NOT redefine the existing ESC Extension Type 133 codes. 135 Section 5.1 in RFC4944 indicates that the Extension Type field may 136 contain additional dispatch values larger than 63, as corrected by 137 [4944-ERRATA]. For the sake of interoperability, the new dispatch 138 type (EET) MUST NOT modify the behavior of existing dispatch types 139 [RFC4944]. 141 3.1. Interaction with other RFC4944 implementations 143 It is expected that RFC4944 existing implementations are not capable 144 of processing ESC extension data bytes as defined in this document. 145 However, implementers have to assume that existing implementation 146 that attempt to process an EET unknown to them will simply drop the 147 packet or ignore the ESC dispatch bytes. 149 If an implementation following this document, during processing of 150 the received packet reaches an ESC byte for which it does not 151 understand the extension bytes (EET), it MUST drop that packet. 152 However, it is important to clarify that a router node SHOULD forward 153 a 6lowpan packet with the EET bytes as long as it does not attempt to 154 process any unknown ESC extension bytes. 156 Sequence Of dispatch bytes and ESC bytes: Multiple ESC extension 157 bytes may appear in a packet. The ESC bytes can appear as the first, 158 last or middle dispatch bytes. However, a packet will get dropped by 159 any node that does not understand the EET at the beginning of the 160 packet. The closer to the end of the packet are the EET's, the 161 higher chance there is that a legacy node will recognize and 162 successfully process some dispatch type [RFC4944] before the EET and 163 then ignore the EET instead of dropping the entire packet. 165 3.2. ESC Extension Bytes Typical Sequence 167 ESC Extension bytes sequence and order with respect to 6LoWPAN Mesh 168 header and LoWPAN_IPHC header are described below. When LOWPAN_IPHC 169 dispatch type is present, ESC bytes MUST appear before the 170 LOWPAN_IPHC dispatch type in order to maintain backward compatibility 171 with RFC6282 section 3.2. The following diagrams provide examples of 172 ESC extension byte usages: 174 A LoWPAN encapsulated IPv6 Header compressed packet: 176 +-------+------+--------+--------+-----------------+--------+ 177 | ESC | EET | EDP |Dispatch| LOWPAN_IPHC hdr | Payld | 178 +-------+------+--------+--------+-----------------+--------+ 180 A LoWPAN_IPHC Header, Mesh header and an ESC extension byte: 182 +-----+-----+-----+----+------+-------+---------------+------+ 183 |M typ| Mhdr| ESC | EET|EDP |Disptch|LOWPAN_IPHC hdr| Payld| 184 +-----+-----+-----+----+------+-------+---------------+------+ 186 A Mesh header with ESC bytes 187 +-------+-------+-----+-----+-------+ 188 | M Typ | M Hdr | ESC | EET |EDP | 189 +-------+-------+-----+-----+-------+ 191 With Fragment header 193 +-------+-------+--------+------+-----+-----+-------+ 194 | M Typ | M Hdr | F Typ | F hdr|ESC | EET | EDP | 195 +-------+-------+--------+------+-----+-----+-------+ 197 ESC byte as a LowPAN encapsulation 199 +--------+--------+--------+ 200 | ESC | EET | EDP | 201 +--------+--------+--------+ 203 Figure 2: A 6lowpan packet with ESC Bytes 205 3.3. ITU-T G.9903 ESC type usage 207 The ESC dispatch type is used in [G3-PLC] to provide native mesh 208 routing and bootstrapping functionalities. The ITU-T recommendation 209 defines command IDs in the [G3-PLC] section 9.4.2.3 which operates 210 like ESC Extension type field. The command ID values are 0x01 to 211 0x1F. 213 The frame format is defined as follows: 215 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 1 216 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 217 |0 1| ESC | Command ID | Command Payload 218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 220 Figure 3: G.9903 Frame Format with ESC Byte 222 3.4. NALP and ESC bytes 224 According to RFC4944 [RFC4944] section 5.1, NALP dispatch bytes are 225 reserved for use as a kind of escape code for identification of non- 226 6lowpan payloads. Since ESC bytes are part of 6lowpan dispatch types 227 (extended), they are orthogonal to NALP bytes. 229 This document clarifies that NALP dispatch codes only provide an 230 escape method for non-6LoWPAN payloads when they appear as the 231 initial byte of a LoWPAN encapsulation, and that the potential 232 meaning of their appearance in any other location is reserved for 233 future use. 235 4. IANA Considerations 237 This document requests IANA to register the 'ESC Extension Type' 238 values per the policy 'Specification Required' [RFC5226], following 239 the same policy as in the IANA section of [RFC4944]. For each 240 Extension Type (except the Reserved values) the specification MUST 241 define corresponding Extended Dispatch Payload frame bytes for the 242 receiver implementation to read the ESC bytes in an interoperable 243 fashion. 245 [RFC5226] section 4.1 also indicates that "Specification Required" 246 implies a Designated Expert review of the public specification 247 requesting registration of the ESC Extension Type values. 249 The allocation of code points should follow the guidelines on "Usage 250 Of ESC Dispatch Bytes" and the typical example sections. ESC 251 Extension type code points MUST be used in conjunction with 6lo 252 protocols following [RFC4944] or its derivatives. The requesting 253 document MUST specify how the ESC dispatch bytes will be used along 254 with 6LOWPAN headers in their use cases. 256 The initial values for the 'ESC Extension Type' fields are: 258 +-------+---------------------------------+---------------+ 259 | Value | Description | Reference | 260 +-------+---------------------------------+---------------+ 261 | 0 | Reserved for future use | This document | 262 | | | | 263 | 1-31 | Used by ITU-T G.9903 and G.9905 | ITU-T G.9903 &| 264 | | Command IDs | ITU-T G.9905 | 265 | | | | 266 | 32-254| Unassigned | This document | 267 | |(Reserved for future IANA | | 268 | | Assignment-- Spec Required) | | 269 | | | | 270 | 255 | Reserved for future use | This document | 271 +-------+---------------------------------+---------------+ 273 Figure 4: Initial Values for IANA Registry 275 5. Security Considerations 277 There are no additional security threats due to the assignments of 278 ESC byte usage described in this document. Furthermore, this 279 document forbids defining any extended dispatch values or extension 280 types that modify the behavior of existing Dispatch types. 282 6. Acknowledgements 284 The authors would like to thank the members of the 6lo WG for their 285 comments. Many thanks to Carsten Bormann, Ralph Droms, Thierry Lys, 286 Cedric Lavenu, Pascal Thubert for discussions regarding the bits 287 allocation issues, which led to this document. Jonathan Hui and 288 Robert Cragie provided extensive reviews and guidance for 289 interoperability. The authors acknowledge the comments from the 290 following people that helped shape this document: Paul Duffy, Don 291 Sturek, Michael Richardson, Xavier Vilajosana and Scott Mansfield. 292 Thanks to Brian Haberman, our document shepherd, for guidance in the 293 IANA section. 295 7. References 296 7.1. Normative References 298 [4944-ERRATA] 299 "https://www.rfc-editor.org/errata_search.php?rfc=4944". 301 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 302 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 303 RFC2119, March 1997, 304 . 306 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 307 "Transmission of IPv6 Packets over IEEE 802.15.4 308 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, 309 . 311 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 312 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 313 DOI 10.17487/RFC6282, September 2011, 314 . 316 7.2. Informative References 318 [6LOWPAN-IANA] 319 "https://www.iana.org/assignments/_6lowpan-parameters/ 320 _6lowpan-parameters.xhtml". 322 [6loCHART] 323 "https://datatracker.ietf.org/wg/6lo/charter". 325 [G3-PLC] "http://www.itu.int/rec/T-REC-G.9903-201402-I". 327 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 328 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 329 DOI 10.17487/RFC5226, May 2008, 330 . 332 Authors' Addresses 334 Samita Chakrabarti 335 San Jose, CA 336 USA 338 Email: samitac.ietf@gmail.com 339 Gabriel Montenegro 340 Microsoft 341 USA 343 Email: gabriel.montenegro@microsoft.com 345 Ralph Droms 346 USA 348 Email: rdroms@gmail.com 350 James Woodyatt 351 Nest 352 Mountain View, CA 353 USA 355 Email: jhw@netstlabs.com