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Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Downref: Normative reference to an Informational RFC: RFC 7665 ** Obsolete normative reference: RFC 8321 (Obsoleted by RFC 9341) == Outdated reference: A later version (-06) exists of draft-song-mpls-eh-indicator-04 Summary: 3 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MPLS H. Song, Ed. 3 Internet-Draft Futurewei Technologies 4 Intended status: Standards Track Z. Li 5 Expires: 14 July 2022 T. Zhou 6 Huawei 7 L. Andersson 8 Bronze Dragon Consulting 9 Z. Zhang 10 Juniper Networks 11 10 January 2022 13 MPLS Extension Header 14 draft-song-mpls-extension-header-06 16 Abstract 18 Motivated by the need to support multiple in-network services and 19 functions in an MPLS network, this document describes a generic and 20 extensible method to encapsulate extension headers into MPLS packets. 21 The encapsulation method allows stacking multiple extension headers 22 and quickly accessing any of them as well as the original upper layer 23 protocol header and payload. We show how the extension header can be 24 used to support several new network applications and optimize some 25 existing network services. 27 Requirements Language 29 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 30 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 31 "OPTIONAL" in this document are to be interpreted as described in BCP 32 14 [RFC2119][RFC8174] when, and only when, they appear in all 33 capitals, as shown here. 35 Status of This Memo 37 This Internet-Draft is submitted in full conformance with the 38 provisions of BCP 78 and BCP 79. 40 Internet-Drafts are working documents of the Internet Engineering 41 Task Force (IETF). Note that other groups may also distribute 42 working documents as Internet-Drafts. The list of current Internet- 43 Drafts is at https://datatracker.ietf.org/drafts/current/. 45 Internet-Drafts are draft documents valid for a maximum of six months 46 and may be updated, replaced, or obsoleted by other documents at any 47 time. It is inappropriate to use Internet-Drafts as reference 48 material or to cite them other than as "work in progress." 49 This Internet-Draft will expire on 14 July 2022. 51 Copyright Notice 53 Copyright (c) 2022 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 58 license-info) in effect on the date of publication of this document. 59 Please review these documents carefully, as they describe your rights 60 and restrictions with respect to this document. Code Components 61 extracted from this document must include Revised BSD License text as 62 described in Section 4.e of the Trust Legal Provisions and are 63 provided without warranty as described in the Revised BSD License. 65 Table of Contents 67 1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 2 68 2. MPLS Extension Header . . . . . . . . . . . . . . . . . . . . 4 69 3. Type of MPLS Extension Headers . . . . . . . . . . . . . . . 8 70 4. Operation on MPLS Extension Headers . . . . . . . . . . . . . 8 71 5. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 9 72 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 73 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 74 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 10 75 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 76 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 77 10.1. Normative References . . . . . . . . . . . . . . . . . . 10 78 10.2. Informative References . . . . . . . . . . . . . . . . . 11 79 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 81 1. Motivation 83 Some applications require adding instructions and/or metadata to user 84 packets within a network. Such examples include In-situ OAM (IOAM) 85 [I-D.ietf-ippm-ioam-data] and Service Function Chaining (SFC) 86 [RFC7665]. New applications are emerging. It is possible that the 87 instructions and/or metadata for multiple applications are stacked 88 together in one packet to support a compound service. 90 Conceivably, such instructions and/or metadata would be encoded as 91 new headers and encapsulated in user packets. Such headers may 92 require to be processed in fast path or in slow path. Moreover, such 93 headers may require being attended at each hop on the forwarding path 94 (i.e., hop-by-hop or HBH) or at designated end nodes (i.e., end-to- 95 end or E2E). 97 The encapsulation of the new header(s) poses some challenges to MPLS 98 networks, because the MPLS protocol header contains no explicit 99 indicator for the upper layer protocols by design. We leave the 100 discussion on the indicator of new header(s) in an MPLS packet to 101 another companion document [I-D.song-mpls-eh-indicator]. In this 102 document, we focus on the encode and encapsulation of new headers in 103 an MPLS packet. 105 The similar problem has been tackled for some particular application 106 before. However, these solutions have some drawbacks: 108 * The solutions rely on either the built-in next-protocol indicator 109 in the header or the knowledge of the format and size of the 110 header to access the following packet data. The node is required 111 to be able to parse the new header, which is unrealistic in an 112 incremental deployment environment. 114 * These works only provide piecemeal solution which assumes the new 115 header is the only extra header and its location in the packet is 116 fixed by default. It is impossible or difficult to support 117 multiple new headers in one packet due to the conflicted 118 assumption. 120 * Some previous work such as G-ACH [RFC5586] was explicitly defined 121 for control channel only but what we need is the user packet 122 service. 124 To solve these problems, we introduce extension header as a general 125 and extensible means to support new in-network functions and 126 applications in MPLS networks. The idea is similar to IPv6 extension 127 headers which offer a huge innovation potential (e.g, network 128 security, SRv6 [RFC8754], network programming 129 [I-D.ietf-spring-srv6-network-programming], SFC 130 [I-D.xu-clad-spring-sr-service-chaining], etc.). Thanks to the 131 existence of extension headers, it is straightforward to introduce 132 new in-network services into IPv6 networks. For example, it has been 133 proposed to carry IOAM header [I-D.brockners-inband-oam-transport] as 134 a new extension header option in IPv6 networks. 136 Nevertheless, IPv6 EH is not perfect either. It has three issues: 138 * IPv6's header is large compared to MPLS, claiming extra bandwidth 139 overhead and complicating the packet processing. We prefer to 140 retain the header compactness in MPLS networks. 142 * IPv6's extension headers are chained with the original upper layer 143 protocol headers in a flat stack. One must scan all the extension 144 headers to access the upper layer protocol headers and the 145 payload. This is inconvenient and raises some performance 146 concerns for some applications(e.g., DPI and ECMP). The new 147 scheme for MPLS header extension needs to address these issues 148 too. 150 * [RFC8200] enforces many constraints to IPv6 extension headers 151 (e.g., EH can only be added or deleted by the end nodes specified 152 by the IP addresses in the IPv6 header, and there is only one Hop- 153 by-Hop EH that can be processed on the path nodes), which are not 154 suitable for MPLS networks. For example, MPLS label stacks are 155 added and changed in network, and there could be tunnel within 156 tunnel, so the extension headers need more flexibility. 158 2. MPLS Extension Header 160 From the previous discussion, we have laid out the design 161 requirements to support extension headers in MPLS networks: 163 Performance: Unnecessary label stack scanning for a label and the 164 full extension header stack scanning for the upper layer protocol 165 should be avoided. The extension headers a node needs to process 166 should be located as close to the MPLS label stack as possible. 167 Each extension header is better to serve only one application to 168 avoid the need of packing multiple TLV options in one extension 169 header. 171 Scalability: New applications can be supported by introducing new 172 extension headers. Multiple extension headers can be easily 173 stacked together to support multiple services simultaneously. 175 Backward Compatibility: Legacy devices which do not recognize the 176 extension header option should still be able to forward the 177 packets as usual. If a device recognize some of the extension 178 headers but not the others in an extension header stack, it can 179 process the known headers only while ignoring the others. 181 Flexibility: A node can be configured to process or not process any 182 EH. Any tunnel end nodes in the MPLS domain can add new EH to the 183 packets which shall be removed on the other end of the tunnel. 185 We assume the MPLS label stack has included some indicator of the 186 extension header(s). The actual extension headers are inserted 187 between the MPLS label stack and the original upper layer packet 188 header. The format of the MPLS packets with extension headers is 189 shown in Figure 1. 191 0 31 192 +--------+--------+--------+--------+ \ 193 | | | 194 ~ MPLS Label Stack ~ | 195 | | | 196 +--------+--------+--------+--------+ | 197 | EH Indicator (TBD) | > MPLS Label Stack 198 +--------+--------+--------+--------+ | (extended with EHI) 199 | | | 200 ~ MPLS Label Stack ~ | 201 | | | 202 +--------+--------+--------+--------+ < 203 | Header of Extension Headers (HEH) | | 204 +--------+--------+--------+--------+ | 205 | | | 206 ~ Extension Header (EH) 1 ~ | 207 | | | 208 +--------+--------+--------+--------+ > MPLS EH Fields 209 ~ ~ | (new) 210 +--------+--------+--------+--------+ | 211 | | | 212 ~ Extension Header (EH) N ~ | 213 | | | 214 +--------+--------+--------+--------+ < 215 | | | 216 ~ Upper Layer Headers/Payload ~ > MPLS Payload 217 | | | (as is) 218 +--------+--------+--------+--------+ / 220 Figure 1: MPLS with Extension Headers 222 Following the MPLS label stack is the 4-octet Header of Extension 223 Headers (HEH), which indicates the total number of extension headers 224 in this packet, the overall length of the extension headers, the type 225 of the original upper layer header, and the type of the next header. 226 The format of the HEH is shown in Figure 2. 228 0 1 2 3 229 0123 4567 89012345 67890123 45678901 230 +----+----+--------+--------+--------+ 231 | R |EHC | EHTL | OUL | NH | 232 +----+----+--------+--------+--------+ 234 Figure 2: HEH Format 236 The meaning of the fields in an HEH is as follows: 238 R: 4-bit reserved. The nibble value means to avoid conflicting with 239 IP version numbers. 241 EHC: 4-bit unsigned integer for the Extension Header Counter. This 242 field keeps the total number of extension headers included in this 243 packet. It does not count the original upper layer protocol 244 headers. At most 15 EHs are allowed in one packet. 246 EHTL: 8-bit unsigned integer for the Extension Header Total Length 247 in 4-octet units. This field keeps the total length of the 248 extension headers in this packet, not including the HEH itself. 250 OUL: 8-bit Original Upper Layer protocol number indicating the 251 original upper layer protocol type. It can be set to "UNKNOWN" if 252 unknown. 254 NH: 8-bit selector for the Next Header. This field identifies the 255 type of the header immediately following the HEH. 257 The value of the reserved nibble needs further consideration. The 258 EHC field can be used to keep track of the number of extension 259 headers when some headers are inserted or removed at some network 260 nodes. The EHTL field can help to skip all the extension headers in 261 one step if the original upper layer protocol headers or payload need 262 to be accessed. The OUL field can help identify the type of the 263 original upper layer protocol. 265 The format of an Extension Header (EH) is shown in Figure 3. 267 0 1 2 3 268 01234567 89012345 67890123 45678901 269 +--------+--------+--------+-------+ 270 | NH | HLEN |EXT | | 271 +--------+--------+--------+ | 272 | | 273 ~ Header Specific Data ~ 274 | | 275 +--------+--------+----------------+ 277 Figure 3: EH Format 279 The meaning of the fields in an EH is as follows: 281 NH: 8-bit indicator for the Next Header. This field identifies the 282 type of the EH immediately following this EH. 284 HLEN: 8-bit unsigned integer for the Extension Header Length in 285 4-octet units, not including the first 4 octets. 287 EXT: 8-bit optional type extension. To save the Next Header numbers 288 and extend the number space, it is possible to use one "Next 289 Header" code to cover a set of sub-types. Each sub-type is 290 assigned a new code in a different name space. This field is 291 optional and it is only specified for some specific EH type. 293 Header Specific Data: Variable length field for the specification of 294 the EH. This field is 4-octet aligned. 296 The extension headers as well as the first original upper layer 297 protocol header are chained together through the NH field in HEH and 298 EHs. The encoding of NH can share the same value registry for IPv4/ 299 IPv6 protocol numbers. Values for new EH types shall be assigned by 300 IANA. 302 Specifically, the NH field of the last EH in a chain can have some 303 special values, which shall be assigned by IANA as well: 305 NONE (No Next Header): Indicates that there is no other header and 306 payload after this header. This can be used to transport packets 307 with only extension header(s), for example, the control packets 308 for control or the probe packets for measurements. Note that 309 value 59 was reserved for "IPv6 No Next Header" indicator. It may 310 be possible for MPLS EH to share this value. 312 UNKNOWN (Unknown Next Header): Indicates that the type of the header 313 after this header is unknown. This is intended to be compatible 314 with the original MPLS design in which the upper layer protocol 315 type is unknown from the MPLS header alone. 317 MPLS: Indicates that the original upper layer protocol is still MPLS 318 and another MPLS label stack follows. 320 Note that the original upper layer protocol can be of type "MPLS", 321 which implies that in a packet there might be multiple label stacks 322 separated by EHs. Having more than one independent label stack is 323 not new. For example, A Bier header could separate the transport/ 324 bier labels and the payload labels; An MPLS PW network could be 325 implemented on the top of another infrastructure MPLS network. In 326 such cases, we have the flexibility to apply different services to 327 different label stacks. 329 3. Type of MPLS Extension Headers 331 Basically, there are two types of MPLS EHs: HBH and E2E. E2E means 332 that the EH is only supposed to be inserted/removed and processed at 333 the MPLS tunnel end points where the MPLS header is inserted or 334 removed. The EHs that need to be processed on path nodes within the 335 MPLS tunnel are of the HBH type. However, any node in the tunnel can 336 be configured to ignore an HBH EH, even if it is capable of 337 processing it. 339 If there are two types of EHs in a packet, the HBH EHs must take 340 precedence over the E2E EHs. 342 Making a distinction of the EH types and ordering the EHs in a packet 343 help improve the forwardidng performance. For example, if a node 344 within an MPLS tunnel finds only E2E EHs in a packet, it can avoid 345 scanning the EH list. 347 4. Operation on MPLS Extension Headers 349 When the first EH X needs to be added to an MPLS packet, an EH 350 indicator is inserted into the proper location in the MPLS label 351 stack. A HEH is then inserted after the MPLS label stack, in which 352 EHCNT is set to 1, EHTLEN is set to the length of X in 4-octet units, 353 and NH is set to the header value of X. At last, X is inserted after 354 the HEH, in which NH and HELN are set accordingly. Note that if this 355 operation happens at a PE device, the upper layer protocol is known 356 before the MPLS encapsulation, so its value can be saved in the NH 357 field if desired. Otherwise, the NH field is filled with the value 358 of "UNKNOWN". 360 When an EH Y needs to be added to an MPLS packet which already 361 contains extension header(s), the EHCNT and EHTLEN in the HEH are 362 updated accordingly (i.e., EHCNT is incremented by 1 and EHTLEN is 363 incremented by the size of Y in 4-octet units). Then a proper 364 location for Y in the EH chain is located. Y is inserted at this 365 location. The NH field of Y is copied from the previous EH's NH 366 field (or from the HEH's NH field, if Y is the first EH in the 367 chain). The previous EH's NH value, or, if Y is the first EH in the 368 chain, the HEH's NH, is set to the header value of Y. 370 Deleting an EH simply reverses the above operation. If the deleted 371 EH is the last one, the EH indicator and HEH can also be removed. 373 When processing an MPLS packet with extension headers, the node needs 374 to scan through the entire EH chain and process the EH one by one. 375 The node should ignore any unrecognized EH or the EH that is 376 configured as "No Processing". 378 The EH can be categorized into HBH or E2E. Since EHs are ordered 379 based on their type(i.e., HBH EHs are located before E2E EHs), a node 380 can avoid some unnecessary EH scan. 382 5. Use Cases 384 In this section, we show how MPLS extension header can be used to 385 support several new network applications. 387 In-situ OAM: In-situ OAM (IOAM) records flow OAM information within 388 user packets while the packets traverse a network. The 389 instruction and collected data are kept in an IOAM header 390 [I-D.ietf-ippm-ioam-data]. When applying IOAM in an MPLS network, 391 the IOAM header can be encapsulated as an MPLS extension header. 393 Network Telemetry and Measurement: A network telemetry and 394 instruction header can be carried as an extension header to 395 instruct a node what type of network measurements should be done. 396 For example, the method described in [RFC8321] can be implemented 397 in MPLS networks since the EH provides a natural way to color MPLS 398 packets. 400 Network Security: Security related functions often require user 401 packets to carry some metadata. In a DoS limiting network 402 architecture, a "packet passport" header is used to embed packet 403 authentication information for each node to verify. 405 Segment Routing and Network Programming: MPLS extension header can 406 support the implementation of a new flavor of the MPLS-based 407 segment routing, with better performance and richer 408 functionalities. The details will be described in another draft. 410 With MPLS extension headers, multiple in-network applications can be 411 stacked together. For example, IOAM and SFC can be applied at the 412 same time to support network OAM and service function chaining. A 413 node can stop scanning the extension header stack if all the known 414 headers it can process have been located. For example, if IOAM is 415 the first EH in a stack and a node is configured to process IOAM 416 only, it will stop searching the EH stack when the IOAM EH is found. 418 6. Security Considerations 420 TBD 422 7. IANA Considerations 424 This document requests IANA to assign two new Internet Protocol 425 Numbers from the "Protocol Numbers" Registry to indicate "No Next 426 Header" and "Unknown Next Header". 428 This document does not create any other new registries. 430 8. Contributors 432 The other contributors of this document are listed as follows. 434 * James Guichard 436 * Stewart Bryant 438 * Andrew Malis 440 9. Acknowledgments 442 TBD. 444 10. References 446 10.1. Normative References 448 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 449 Requirement Levels", BCP 14, RFC 2119, 450 DOI 10.17487/RFC2119, March 1997, 451 . 453 [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function 454 Chaining (SFC) Architecture", RFC 7665, 455 DOI 10.17487/RFC7665, October 2015, 456 . 458 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 459 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 460 May 2017, . 462 [RFC8321] Fioccola, G., Ed., Capello, A., Cociglio, M., Castaldelli, 463 L., Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi, 464 "Alternate-Marking Method for Passive and Hybrid 465 Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321, 466 January 2018, . 468 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 469 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 470 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 471 . 473 10.2. Informative References 475 [I-D.brockners-inband-oam-transport] 476 Brockners, F., Bhandari, S., Govindan, V. P., Pignataro, 477 C., Gredler, H., Leddy, J., Youell, S., Mizrahi, T., 478 Mozes, D., Lapukhov, P., and R. Chang, "Encapsulations for 479 In-situ OAM Data", Work in Progress, Internet-Draft, 480 draft-brockners-inband-oam-transport-05, 3 July 2017, 481 . 484 [I-D.ietf-ippm-ioam-data] 485 Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields 486 for In-situ OAM", Work in Progress, Internet-Draft, draft- 487 ietf-ippm-ioam-data-17, 13 December 2021, 488 . 491 [I-D.ietf-spring-srv6-network-programming] 492 Filsfils, C., Garvia, P. C., Leddy, J., Voyer, D., 493 Matsushima, S., and Z. Li, "Segment Routing over IPv6 494 (SRv6) Network Programming", Work in Progress, Internet- 495 Draft, draft-ietf-spring-srv6-network-programming-28, 29 496 December 2020, . 499 [I-D.song-mpls-eh-indicator] 500 Song, H., Li, Z., Zhou, T., and L. Andersson, "Options for 501 MPLS Extension Header Indicator", Work in Progress, 502 Internet-Draft, draft-song-mpls-eh-indicator-04, 3 January 503 2022, . 506 [I-D.xu-clad-spring-sr-service-chaining] 507 Clad, F., Xu, X., Filsfils, C., Bernier, D., Decraene, B., 508 Yadlapalli, C., Henderickx, W., Salsano, S., and S. Ma, 509 "Segment Routing for Service Chaining", Work in Progress, 510 Internet-Draft, draft-xu-clad-spring-sr-service-chaining- 511 00, 22 December 2017, . 514 [RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed., 515 "MPLS Generic Associated Channel", RFC 5586, 516 DOI 10.17487/RFC5586, June 2009, 517 . 519 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 520 (IPv6) Specification", STD 86, RFC 8200, 521 DOI 10.17487/RFC8200, July 2017, 522 . 524 Authors' Addresses 526 Haoyu Song (editor) 527 Futurewei Technologies 528 Santa Clara, 529 United States of America 531 Email: haoyu.song@futurewei.com 533 Zhenbin Li 534 Huawei 535 Beijing 536 P.R. China 538 Email: lizhenbin@huawei.com 540 Tianran Zhou 541 Huawei 542 Beijing 543 P.R. China 545 Email: zhoutianran@huawei.com 547 Loa Andersson 548 Bronze Dragon Consulting 549 Stockholm 550 Sweden 552 Email: loa@pi.nu 553 Zhaohui Zhang 554 Juniper Networks 555 Boston, 556 United States of America 558 Email: zzhang@juniper.net