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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reference to an Informational RFC: RFC 7665 ** Obsolete normative reference: RFC 8321 (Obsoleted by RFC 9341) == Outdated reference: A later version (-17) exists of draft-ietf-ippm-ioam-data-12 == Outdated reference: A later version (-06) exists of draft-song-mpls-eh-indicator-01 Summary: 3 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--).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: October 31, 2021 T. Zhou 6 Huawei 7 L. Andersson 8 Bronze Dragon Consulting 9 April 29, 2021 11 MPLS Extension Header 12 draft-song-mpls-extension-header-04 14 Abstract 16 Motivated by the need to support multiple in-network services and 17 functions in an MPLS network, this document describes a generic and 18 extensible method to encapsulate extension headers into MPLS packets. 19 The encapsulation method allows stacking multiple extension headers 20 and quickly accessing any of them as well as the original upper layer 21 protocol header and payload. We show how the extension header can be 22 used to support several new network applications and optimize some 23 existing network services. 25 Requirements Language 27 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 28 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 29 "OPTIONAL" in this document are to be interpreted as described in BCP 30 14 [RFC2119][RFC8174] when, and only when, they appear in all 31 capitals, as shown here. 33 Status of This Memo 35 This Internet-Draft is submitted in full conformance with the 36 provisions of BCP 78 and BCP 79. 38 Internet-Drafts are working documents of the Internet Engineering 39 Task Force (IETF). Note that other groups may also distribute 40 working documents as Internet-Drafts. The list of current Internet- 41 Drafts is at https://datatracker.ietf.org/drafts/current/. 43 Internet-Drafts are draft documents valid for a maximum of six months 44 and may be updated, replaced, or obsoleted by other documents at any 45 time. It is inappropriate to use Internet-Drafts as reference 46 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on October 31, 2021. 50 Copyright Notice 52 Copyright (c) 2021 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (https://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 2 68 2. MPLS Extension Header . . . . . . . . . . . . . . . . . . . . 4 69 3. Type of MPLS Extension Headers . . . . . . . . . . . . . . . 7 70 4. Operation on MPLS Extension Headers . . . . . . . . . . . . . 7 71 5. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 8 72 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 73 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 74 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9 75 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 76 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 77 10.1. Normative References . . . . . . . . . . . . . . . . . . 9 78 10.2. Informative References . . . . . . . . . . . . . . . . . 10 79 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 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 o 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 o 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 o 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 o 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 o 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 o [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, and the 225 type of the next header. The format of the HEH is shown in Figure 2. 227 0 1 2 3 228 0123 45678901 234567890123 45678901 229 +----+--------+------------+--------+ 230 | R | EHCNT | EHTLEN | NH | 231 +----+--------+------------+--------+ 233 Figure 2: HEH Format 235 The meaning of the fields in an HEH is as follows: 237 R: 4-bit reserved. 239 EHCNT: 8-bit unsigned integer for the Extension Header Counter. 240 This field keeps the total number of extension headers included in 241 this packet. It does not count the original upper layer protocol 242 headers. 244 EHTLEN: 12-bit unsigned integer for the Extension Header Total 245 Length in 4-octet units. This field keeps the total length of the 246 extension headers in this packet, not including the HEH itself. 248 NH: 8-bit selector for the Next Header. This field identifies the 249 type of the header immediately following the HEH. 251 The value of the reserved nibble needs further consideration. The 252 EHCNT field can be used to keep track of the number of extension 253 headers when some headers are inserted or removed at some network 254 nodes. The EHLEN field can help to skip all the extension headers in 255 one step if the original upper layer protocol headers or payload need 256 to be accessed. 258 The format of an Extension Header (EH) is shown in Figure 3. 260 0 1 2 3 261 01234567 89012345 6789012345678901 262 +--------+--------+----------------+ 263 | NH | HLEN | | 264 +--------+--------+ + 265 | | 266 ~ Header Specific Data ~ 267 | | 268 +--------+--------+----------------+ 270 Figure 3: EH Format 272 The meaning of the fields in an EH is as follows: 274 NH: 8-bit indicator for the Next Header. This field identifies the 275 type of the EH immediately following this EH. 277 HLEN: 8-bit unsigned integer for the Extension Header Length in 278 4-octet units, not including the first 4 octets. 280 Header Specific Data: Variable length field for the specification of 281 the EH. This field is 4-octet aligned. 283 The extension headers as well as the first original upper layer 284 protocol header are chained together through the NH field in HEH and 285 EHs. The encoding of NH can share the same value registry for IPv4/ 286 IPv6 protocol numbers. Values for new EH types shall be assigned by 287 IANA. 289 Specifically, the NH field of the last EH in a chain can have two 290 special values, which shall be assigned by IANA as well: 292 NONE (No Next Header): Indicates that there is no other header and 293 payload after this header. This can be used to transport packets 294 with only extension header(s), for example, the control packets 295 for control or the probe packets for measurements. Note that 296 value 59 was reserved for "IPv6 No Next Header" indicator. It may 297 be possible for MPLS EH to share this value. 299 UNKNOWN (Unknown Next Header): Indicates that the type of the header 300 after this header is unknown. This is intended to be compatible 301 with the original MPLS design in which the upper layer protocol 302 type is unknown from the MPLS header alone. 304 3. Type of MPLS Extension Headers 306 Basically, there are two types of MPLS EHs: HBH and E2E. E2E means 307 that the EH is only supposed to be inserted/removed and processed at 308 the MPLS tunnel end points where the MPLS header is inserted or 309 removed. The EHs that need to be processed on path nodes within the 310 MPLS tunnel are of the HBH type. However, any node in the tunnel can 311 be configured to ignore an HBH EH, even if it is capable of 312 processing it. 314 If there are two types of EHs in a packet, the HBH EHs must take 315 precedence over the E2E EHs. 317 Making a distinction of the EH types and ordering the EHs in a packet 318 help improve the forwardidng performance. For example, if a node 319 within an MPLS tunnel finds only E2E EHs in a packet, it can avoid 320 scanning the EH list. 322 4. Operation on MPLS Extension Headers 324 When the first EH X needs to be added to an MPLS packet, an EH 325 indicator is inserted into the proper location in the MPLS label 326 stack. A HEH is then inserted after the MPLS label stack, in which 327 EHCNT is set to 1, EHTLEN is set to the length of X in 4-octet units, 328 and NH is set to the header value of X. At last, X is inserted after 329 the HEH, in which NH and HELN are set accordingly. Note that if this 330 operation happens at a PE device, the upper layer protocol is known 331 before the MPLS encapsulation, so its value can be saved in the NH 332 field if desired. Otherwise, the NH field is filled with the value 333 of "UNKNOWN". 335 When an EH Y needs to be added to an MPLS packet which already 336 contains extension header(s), the EHCNT and EHTLEN in the HEH are 337 updated accordingly (i.e., EHCNT is incremented by 1 and EHTLEN is 338 incremented by the size of Y in 4-octet units). Then a proper 339 location for Y in the EH chain is located. Y is inserted at this 340 location. The NH field of Y is copied from the previous EH's NH 341 field (or from the HEH's NH field, if Y is the first EH in the 342 chain). The previous EH's NH value, or, if Y is the first EH in the 343 chain, the HEH's NH, is set to the header value of Y. 345 Deleting an EH simply reverses the above operation. If the deleted 346 EH is the last one, the EH indicator and HEH can also be removed. 348 When processing an MPLS packet with extension headers, the node needs 349 to scan through the entire EH chain and process the EH one by one. 350 The node should ignore any unrecognized EH or the EH that is 351 configured as "No Processing". 353 The EH can be categorized into HBH or E2E. Since EHs are ordered 354 based on their type(i.e., HBH EHs are located before E2E EHs), a node 355 can avoid some unnecessary EH scan. 357 5. Use Cases 359 In this section, we show how MPLS extension header can be used to 360 support several new network applications. 362 In-situ OAM: In-situ OAM (IOAM) records flow OAM information within 363 user packets while the packets traverse a network. The 364 instruction and collected data are kept in an IOAM header 365 [I-D.ietf-ippm-ioam-data]. When applying IOAM in an MPLS network, 366 the IOAM header can be encapsulated as an MPLS extension header. 368 Network Telemetry and Measurement: A network telemetry and 369 instruction header can be carried as an extension header to 370 instruct a node what type of network measurements should be done. 371 For example, the method described in [RFC8321] can be implemented 372 in MPLS networks since the EH provides a natural way to color MPLS 373 packets. 375 Network Security: Security related functions often require user 376 packets to carry some metadata. In a DoS limiting network 377 architecture, a "packet passport" header is used to embed packet 378 authentication information for each node to verify. 380 Segment Routing and Network Programming: MPLS extension header can 381 support the implementation of a new flavor of the MPLS-based 382 segment routing, with better performance and richer 383 functionalities. The details will be described in another draft. 385 With MPLS extension headers, multiple in-network applications can be 386 stacked together. For example, IOAM and SFC can be applied at the 387 same time to support network OAM and service function chaining. A 388 node can stop scanning the extension header stack if all the known 389 headers it can process have been located. For example, if IOAM is 390 the first EH in a stack and a node is configured to process IOAM 391 only, it will stop searching the EH stack when the IOAM EH is found. 393 6. Security Considerations 395 TBD 397 7. IANA Considerations 399 This document requests IANA to assign two new Internet Protocol 400 Numbers from the "Protocol Numbers" Registry to indicate "No Next 401 Header" and "Unknown Next Header". 403 This document does not create any other new registries. 405 8. Contributors 407 The other contributors of this document are listed as follows. 409 o James Guichard 411 o Stewart Bryant 413 o Andrew Malis 415 9. Acknowledgments 417 TBD. 419 10. References 421 10.1. Normative References 423 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 424 Requirement Levels", BCP 14, RFC 2119, 425 DOI 10.17487/RFC2119, March 1997, 426 . 428 [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function 429 Chaining (SFC) Architecture", RFC 7665, 430 DOI 10.17487/RFC7665, October 2015, 431 . 433 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 434 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 435 May 2017, . 437 [RFC8321] Fioccola, G., Ed., Capello, A., Cociglio, M., Castaldelli, 438 L., Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi, 439 "Alternate-Marking Method for Passive and Hybrid 440 Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321, 441 January 2018, . 443 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 444 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 445 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 446 . 448 10.2. Informative References 450 [I-D.brockners-inband-oam-transport] 451 Brockners, F., Bhandari, S., Govindan, V., Pignataro, C., 452 Gredler, H., Leddy, J., Youell, S., Mizrahi, T., Mozes, 453 D., Lapukhov, P., and R. Chang, "Encapsulations for In- 454 situ OAM Data", draft-brockners-inband-oam-transport-05 455 (work in progress), July 2017. 457 [I-D.ietf-ippm-ioam-data] 458 Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields 459 for In-situ OAM", draft-ietf-ippm-ioam-data-12 (work in 460 progress), February 2021. 462 [I-D.ietf-spring-srv6-network-programming] 463 Filsfils, C., Camarillo, P., Leddy, J., Voyer, D., 464 Matsushima, S., and Z. Li, "SRv6 Network Programming", 465 draft-ietf-spring-srv6-network-programming-28 (work in 466 progress), December 2020. 468 [I-D.song-mpls-eh-indicator] 469 Song, H., Li, Z., Zhou, T., and L. Andersson, "Options for 470 MPLS Extension Header Indicator", draft-song-mpls-eh- 471 indicator-01 (work in progress), March 2021. 473 [I-D.xu-clad-spring-sr-service-chaining] 474 Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca, 475 d., Decraene, B., Yadlapalli, C., Henderickx, W., Salsano, 476 S., and S. Ma, "Segment Routing for Service Chaining", 477 draft-xu-clad-spring-sr-service-chaining-00 (work in 478 progress), December 2017. 480 [RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed., 481 "MPLS Generic Associated Channel", RFC 5586, 482 DOI 10.17487/RFC5586, June 2009, 483 . 485 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 486 (IPv6) Specification", STD 86, RFC 8200, 487 DOI 10.17487/RFC8200, July 2017, 488 . 490 Authors' Addresses 492 Haoyu Song (editor) 493 Futurewei Technologies 494 2330 Central Expressway 495 Santa Clara 496 USA 498 Email: haoyu.song@futurewei.com 500 Zhenbin Li 501 Huawei 502 156 Beiqing Road 503 Beijing, 100095 504 P.R. China 506 Email: lizhenbin@huawei.com 508 Tianran Zhou 509 Huawei 510 156 Beiqing Road 511 Beijing, 100095 512 P.R. China 514 Email: zhoutianran@huawei.com 515 Loa Andersson 516 Bronze Dragon Consulting 518 Stockholm 519 Sweden 521 Email: loa@pi.nu