idnits 2.17.00 (12 Aug 2021) /tmp/idnits39710/draft-ietf-spring-nsh-sr-08.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == There are 1 instance of lines with non-RFC6890-compliant IPv4 addresses in the document. If these are example addresses, they should be changed. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (June 29, 2021) is 326 days in the past. 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) -- Looks like a reference, but probably isn't: '0' on line 534 == Missing Reference: 'ThisDocument' is mentioned on line 597, but not defined == Unused Reference: 'RFC6347' is defined on line 647, but no explicit reference was found in the text == Unused Reference: 'RFC8086' is defined on line 656, but no explicit reference was found in the text ** Obsolete normative reference: RFC 6347 (Obsoleted by RFC 9147) ** Downref: Normative reference to an Informational RFC: RFC 7665 ** Downref: Normative reference to an Informational RFC: RFC 8596 == Outdated reference: A later version (-05) exists of draft-ietf-spring-sr-service-programming-03 Summary: 3 errors (**), 0 flaws (~~), 6 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 SPRING J. Guichard, Ed. 3 Internet-Draft Futurewei Technologies 4 Intended status: Standards Track J. Tantsura, Ed. 5 Expires: December 31, 2021 Apstra inc. 6 June 29, 2021 8 Integration of Network Service Header (NSH) and Segment Routing for 9 Service Function Chaining (SFC) 10 draft-ietf-spring-nsh-sr-08 12 Abstract 14 This document describes the integration of Network Service Header 15 (NSH) and Segment Routing (SR), as well as encapsulation details, to 16 support Service Function Chaining (SFC) in an efficient manner while 17 maintaining separation of the service and transport planes as 18 originally intended by the SFC architecture. 20 Combining these technologies allows SR to be used for steering 21 packets between Service Function Forwarders (SFF) along a given 22 Service Function Path (SFP) while NSH has the responsibility for 23 maintaining the integrity of the service plane, the SFC instance 24 context, and any associated metadata. 26 This integration demonstrates that NSH and SR can work cooperatively 27 and provide the network operator with the flexibility to use 28 whichever transport technology makes sense in specific areas of their 29 network infrastructure while still maintaining an end-to-end service 30 plane using NSH. 32 Status of This Memo 34 This Internet-Draft is submitted in full conformance with the 35 provisions of BCP 78 and BCP 79. 37 Internet-Drafts are working documents of the Internet Engineering 38 Task Force (IETF). Note that other groups may also distribute 39 working documents as Internet-Drafts. The list of current Internet- 40 Drafts is at https://datatracker.ietf.org/drafts/current/. 42 Internet-Drafts are draft documents valid for a maximum of six months 43 and may be updated, replaced, or obsoleted by other documents at any 44 time. It is inappropriate to use Internet-Drafts as reference 45 material or to cite them other than as "work in progress." 47 This Internet-Draft will expire on December 31, 2021. 49 Copyright Notice 51 Copyright (c) 2021 IETF Trust and the persons identified as the 52 document authors. All rights reserved. 54 This document is subject to BCP 78 and the IETF Trust's Legal 55 Provisions Relating to IETF Documents 56 (https://trustee.ietf.org/license-info) in effect on the date of 57 publication of this document. Please review these documents 58 carefully, as they describe your rights and restrictions with respect 59 to this document. Code Components extracted from this document must 60 include Simplified BSD License text as described in Section 4.e of 61 the Trust Legal Provisions and are provided without warranty as 62 described in the Simplified BSD License. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 67 1.1. SFC Overview and Rationale . . . . . . . . . . . . . . . 2 68 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4 69 2. SFC within Segment Routing Networks . . . . . . . . . . . . . 4 70 3. NSH-based SFC with SR-MPLS or SRv6 Transport Tunnel . . . . . 5 71 4. SR-based SFC with Integrated NSH Service Plane . . . . . . . 9 72 5. Packet Processing for SR-based SFC . . . . . . . . . . . . . 11 73 5.1. SR-based SFC (SR-MPLS) Packet Processing . . . . . . . . 11 74 5.2. SR-based SFC (SRv6) Packet Processing . . . . . . . . . . 11 75 6. Encapsulation . . . . . . . . . . . . . . . . . . . . . . . . 12 76 6.1. NSH using SR-MPLS Transport . . . . . . . . . . . . . . . 12 77 6.2. NSH using SRv6 Transport . . . . . . . . . . . . . . . . 13 78 7. Security Considerations . . . . . . . . . . . . . . . . . . . 14 79 8. MTU Considerations . . . . . . . . . . . . . . . . . . . . . 14 80 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 81 9.1. Protocol Number for NSH . . . . . . . . . . . . . . . . . 14 82 9.2. SRv6 Endpoint Behavior for NSH . . . . . . . . . . . . . 14 83 10. Contributing Authors . . . . . . . . . . . . . . . . . . . . 15 84 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 85 11.1. Normative References . . . . . . . . . . . . . . . . . . 15 86 11.2. Informative References . . . . . . . . . . . . . . . . . 17 87 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 89 1. Introduction 91 1.1. SFC Overview and Rationale 93 The dynamic enforcement of a service-derived and adequate forwarding 94 policy for packets entering a network that supports advanced Service 95 Functions (SFs) has become a key challenge for network operators. 96 For instance, cascading SFs at the 3GPP (Third Generation Partnership 97 Project) Gi interface (N6 interface in 5G architecture) has shown 98 limitations such as 1) redundant classification features must be 99 supported by many SFs to execute their function, 2) some SFs receive 100 traffic that they are not supposed to process (e.g., TCP proxies 101 receiving UDP traffic) which inevitably affects their dimensioning 102 and performance, and 3) an increased design complexity related to the 103 properly ordered invocation of several SFs. 105 In order to solve those problems, and to decouple the services 106 topology from the underlying physical network while allowing for 107 simplified service delivery, Service Function Chaining (SFC) 108 techniques have been introduced [RFC7665]. 110 SFC techniques are meant to rationalize the service delivery logic 111 and master the companion complexity while optimizing service 112 activation time cycles for operators that need more agile service 113 delivery procedures to better accommodate ever-demanding customer 114 requirements. SFC allows to dynamically create service planes that 115 can be used by specific traffic flows. Each service plane is 116 realized by invoking and chaining the relevant service functions in 117 the right sequence. [RFC7498] provides an overview of the overall 118 SFC problem space and [RFC7665] specifies an SFC data plane 119 architecture. The SFC architecture does not make assumptions on how 120 advanced features (e.g., load-balancing, loose or strict service 121 paths) could be enabled within a domain. Various deployment options 122 are made available to operators with the SFC architecture and this 123 approach is fundamental to accommodate various and heterogeneous 124 deployment contexts. 126 Many approaches can be considered for encoding the information 127 required for SFC purposes (e.g., communicate a service chain pointer, 128 encode a list of loose/explicit paths, or disseminate a service chain 129 identifier together with a set of context information). Likewise, 130 many approaches can also be considered for the channel to be used to 131 carry SFC-specific information (e.g., define a new header, re-use 132 existing packet header fields, or define an IPv6 extension header). 133 Among all these approaches, the IETF created a transport-independent 134 SFC encapsulation scheme: NSH. This design is pragmatic as it does 135 not require replicating the same specification effort as a function 136 of underlying transport encapsulation. Moreover, this design 137 approach encourages consistent SFC-based service delivery in networks 138 enabling distinct transport protocols in various network segments or 139 even between SFFs vs SF-SFF hops. 141 1.2. Requirements Language 143 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 144 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 145 "OPTIONAL" in this document are to be interpreted as described in 146 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, 147 as shown here. 149 2. SFC within Segment Routing Networks 151 As described in [RFC8402], SR leverages the source routing technique. 152 Concretely, a node steers a packet through an SR policy instantiated 153 as an ordered list of instructions called segments. While initially 154 designed for policy-based source routing, SR also finds its 155 application in supporting SFC 156 [I-D.ietf-spring-sr-service-programming]. 158 The two SR data plane encapsulations, namely SR-MPLS [RFC8660] and 159 SRv6 [RFC8754], can both encode an SF as a segment so that an SFC can 160 be specified as a segment list. Nevertheless, and as discussed in 161 [RFC7498], traffic steering is only a subset of the issues that 162 motivated the design of the SFC architecture. Further considerations 163 such as simplifying classification at intermediate SFs and allowing 164 for coordinated behaviors among SFs by means of supplying context 165 information (a.k.a. metadata) should be considered when designing an 166 SFC data plane solution. 168 While each scheme (i.e., NSH-based SFC and SR-based SFC) can work 169 independently, this document describes how the two can be used 170 together in concert and complement each other through two 171 representative application scenarios. Both application scenarios may 172 be supported using either SR-MPLS or SRv6: 174 o NSH-based SFC with SR-based transport plane: in this scenario SR- 175 MPLS or SRv6 provides the transport encapsulation between SFFs 176 while NSH is used to convey and trigger SFC policies. 178 o SR-based SFC with integrated NSH service plane: in this scenario 179 each service hop of the SFC is represented as a segment of the SR 180 segment-list. SR is thus responsible for steering traffic through 181 the necessary SFFs as part of the segment routing path while NSH 182 is responsible for maintaining the service plane and holding the 183 SFC instance context (including associated metadata). 185 It is of course possible to combine both of these two scenarios to 186 support specific deployment requirements and use cases. 188 A classifier MUST assign an NSH Service Path Identifier (SPI) per SR 189 policy so that different traffic flows that use the same NSH Service 190 Function Path (SFP) but different SR policy can coexist on the same 191 SFP without conflict during SFF processing. 193 3. NSH-based SFC with SR-MPLS or SRv6 Transport Tunnel 195 Because of the transport-independent nature of NSH-based service 196 function chains, it is expected that the NSH has broad applicability 197 across different network domains (e.g., access, core). By way of 198 illustration the various SFs involved in a service function chain may 199 be available in a single data center, or spread throughout multiple 200 locations (e.g., data centers, different POPs), depending upon the 201 network operator preference and/or availability of service resources. 202 Regardless of where the SFs are deployed it is necessary to provide 203 traffic steering through a set of SFFs, and when NSH and SR are 204 integrated, this is provided by SR-MPLS or SRv6. 206 The following three figures provide an example of an SFC established 207 flow F that has SF instances located in different data centers, DC1 208 and DC2. For the purpose of illustration, let the SFC's NSH SPI be 209 100 and the initial Service Index (SI) be 255. 211 Referring to Figure 1, packets of flow F in DC1 are classified into 212 an NSH-based SFC and encapsulated after classification as and forwarded to SFF1 214 (which is the first SFF hop for this service function chain). 216 After removing the outer transport encapsulation, SFF1 uses the SPI 217 and SI carried within the NSH encapsulation to determine that it 218 should forward the packet to SF1. SF1 applies its service, 219 decrements the SI by 1, and returns the packet to SFF1. SFF1 220 therefore has when the packet comes back from SF1. 221 SFF1 does a lookup on which results in and forwards the packet to DC1-GW1. 224 +--------------------------- DC1 ----------------------------+ 225 | +-----+ | 226 | | SF1 | | 227 | +--+--+ | 228 | | | 229 | | | 230 | +------------+ | +------------+ | 231 | | N(100,255) | | | F:Inner Pkt| | 232 | +------------+ | +------------+ | 233 | | F:Inner Pkt| | | N(100,254) | | 234 | +------------+ ^ | | +------------+ | 235 | (2) | | | (3) | 236 | | | v | 237 | (1) | (4) | 238 |+------------+ ----> +--+---+ ----> +---------+ | 239 || | NSH | | NSH | | | 240 || Classifier +------------+ SFF1 +--------------+ DC1-GW1 + | 241 || | | | | | | 242 |+------------+ +------+ +---------+ | 243 | | 244 | +------------+ +------------+ | 245 | | N(100,255) | | N(100,254) | | 246 | +------------+ +------------+ | 247 | | F:Inner Pkt| | F:Inner Pkt| | 248 | +------------+ +------------+ | 249 | | 250 +------------------------------------------------------------+ 252 Figure 1: SR for inter-DC SFC - Part 1 254 Referring now to Figure 2, DC1-GW1 performs a lookup using the 255 information conveyed in the NSH which results in . The SR encapsulation, which may be SR-MPLS or 257 SRv6, has the SR segment-list to forward the packet across the inter- 258 DC network to DC2. 260 +----------- Inter DC ----------------+ 261 | (5) | 262 +------+ ----> | +---------+ ----> +---------+ | 263 | | NSH | | | SR | | | 264 + SFF1 +----------|-+ DC1-GW1 +-------------+ DC2-GW1 + | 265 | | | | | | | | 266 +------+ | +---------+ +---------+ | 267 | | 268 | +------------+ | 269 | | S(DC2-GW1) | | 270 | +------------+ | 271 | | N(100,254) | | 272 | +------------+ | 273 | | F:Inner Pkt| | 274 | +------------+ | 275 +-------------------------------------+ 277 Figure 2: SR for inter-DC SFC - Part 2 279 When the packet arrives at DC2, as shown in Figure 3, the SR 280 encapsulation is removed and DC2-GW1 performs a lookup on the NSH 281 which results in next hop: SFF2. When SFF2 receives the packet, it 282 performs a lookup on and determines to forward 283 the packet to SF2. SF2 applies its service, decrements the SI by 1, 284 and returns the packet to SFF2. SFF2 therefore has when the packet comes back from SF2. SFF2 does a lookup on 286 which results in end of service function 287 chain. 289 +------------------------ DC2 ----------------------+ 290 | +-----+ | 291 | | SF2 | | 292 | +--+--+ | 293 | | | 294 | | | 295 | +------------+ | +------------+ | 296 | | N(100,254) | | | F:Inner Pkt| | 297 | +------------+ | +------------+ | 298 | | F:Inner Pkt| | | N(100,253) | | 299 | +------------+ ^ | | +------------+ | 300 | (7) | | | (8) | 301 | | | v | 302 | (6) | (9) | 303 |+----------+ ----> +--+---+ ----> | 304 || | NSH | | IP | 305 || DC2-GW1 +------------+ SFF2 | | 306 || | | | | 307 |+----------+ +------+ | 308 | | 309 | +------------+ +------------+ | 310 | | N(100,254) | | F:Inner Pkt| | 311 | +------------+ +------------+ | 312 | | F:Inner Pkt| | 313 | +------------+ | 314 +---------------------------------------------------+ 316 Figure 3: SR for inter-DC SFC - Part 3 318 The benefits of this scheme are listed hereafter: 320 o The network operator is able to take advantage of the transport- 321 independent nature of the NSH encapsulation, while the service is 322 provisioned end2end. 324 o The network operator is able to take advantage of the traffic 325 steering (traffic engineering) capability of SR where appropriate. 327 o Clear responsibility division and scope between NSH and SR. 329 Note that this scenario is applicable to any case where multiple 330 segments of a service function chain are distributed across multiple 331 domains or where traffic-engineered paths are necessary between SFFs 332 (strict forwarding paths for example). Further note that the above 333 example can also be implemented using end to end segment routing 334 between SFF1 and SFF2. (As such DC-GW1 and DC-GW2 are forwarding the 335 packets based on segment routing instructions and are not looking at 336 the NSH header for forwarding). 338 4. SR-based SFC with Integrated NSH Service Plane 340 In this scenario we assume that the SFs are NSH-aware and therefore 341 it should not be necessary to implement an SFC proxy to achieve SFC. 342 The operation relies upon SR-MPLS or SRv6 to perform SFF-SFF 343 transport and NSH to provide the service plane between SFs thereby 344 maintaining SFC context (e.g., the service plane path referenced by 345 the SPI) and any associated metadata. 347 When a service function chain is established, a packet associated 348 with that chain will first carry an NSH that will be used to maintain 349 the end-to-end service plane through use of the SFC context. The SFC 350 context is used by an SFF to determine the SR segment list for 351 forwarding the packet to the next-hop SFFs. The packet is then 352 encapsulated using the SR header and forwarded in the SR domain 353 following normal SR operations. 355 When a packet has to be forwarded to an SF attached to an SFF, the 356 SFF performs a lookup on the SID associated with the SF. In the case 357 of SR-MPLS this will be a prefix SID [RFC8402]. In the case of SRv6, 358 the behavior described within this document is assigned the name 359 END.NSH, and section 9.2 requests allocation of a code point by IANA. 360 The result of this lookup allows the SFF to retrieve the next hop 361 context between the SFF and SF (e.g., the destination MAC address in 362 case native Ethernet encapsulation is used between SFF and SF). In 363 addition the SFF strips the SR information from the packet, updates 364 the SR information, and saves it to a cache indexed by the NSH 365 Service Path Identifier (SPI) and the Service Index (SI) decremented 366 by 1. This saved SR information is used to encapsulate and forward 367 the packet(s) coming back from the SF. 369 The behavior of remembering the SR segment-list occurs at the end of 370 the regularly defined logic. The behavior of reattaching the 371 segment-list occurs before the SR process of forwarding the packet to 372 the next entry in the segment-list. Both behaviors are further 373 detailed in section 5. 375 When the SF receives the packet, it processes it as usual. The SF 376 may use a Classifier to re-classify the already processed packet. 377 The SF sends the packet back to the SFF. Once the SFF receives this 378 packet, it extracts the SR information using the NSH SPI and SI as 379 the index into the cache. The SFF then pushes the retrieved SR 380 header on top of the NSH header, and forwards the packet to the next 381 segment in the segment-list. The lookup in the SFF cache might fail 382 if re-classification changed NSH SPI and/or SI values. In such a 383 case, SFF must prepare the new SR header to push on top of NSH before 384 forwarding the packet. 386 Figure 4 illustrates an example of this scenario. 388 +-----+ +-----+ 389 | SF1 | | SF2 | 390 +--+--+ +--+--+ 391 | | 392 | | 393 +-----------+ | +-----------+ +-----------+ | +-----------+ 394 |N(100,255) | | |F:Inner Pkt| |N(100,254) | | |F:Inner Pkt| 395 +-----------+ | +-----------+ +-----------+ | +-----------+ 396 |F:Inner Pkt| | |N(100,254) | |F:Inner Pkt| | |N(100,253) | 397 +-----------+ | +-----------+ +-----------+ | +-----------+ 398 (2) ^ | (3) | (5) ^ | (6) | 399 | | | | | | 400 | | v | | v 401 +------------+ (1)--> +-+----+ (4)--> +---+--+ (7)-->IP 402 | | NSHoSR | | NSHoSR | | 403 | Classifier +--------+ SFF1 +---------------------+ SFF2 | 404 | | | | | | 405 +------------+ +------+ +------+ 407 +------------+ +------------+ 408 | S(SF1) | | S(SF2) | 409 +------------+ +------------+ 410 | S(SFF2) | | N(100,254) | 411 +------------+ +------------+ 412 | S(SF2) | | F:Inner Pkt| 413 +------------+ +------------+ 414 | N(100,255) | 415 +------------+ 416 | F:Inner Pkt| 417 +------------+ 419 Figure 4: NSH over SR for SFC 421 The benefits of this scheme include: 423 o It is economically sound for SF vendors to only support one 424 unified SFC solution. The SF is unaware of the SR. 426 o It simplifies the SFF (i.e., the SR router) by nullifying the 427 needs for re-classification and SR proxy. 429 o SR is also used for forwarding purposes including between SFFs. 431 o It takes advantage of SR to eliminate the NSH forwarding state in 432 SFFs. This applies each time strict or loose SFPs are in use. 434 o It requires no interworking as would be the case if SR-MPLS based 435 SFC and NSH-based SFC were deployed as independent mechanisms in 436 different parts of the network. 438 5. Packet Processing for SR-based SFC 440 This section describes the End.NSH behavior (SRv6), Prefix SID 441 behavior (SR-MPLS) and NSH processing logic. 443 5.1. SR-based SFC (SR-MPLS) Packet Processing 445 When an SFF receives a packet destined to S and S is a local prefix 446 SID associated with an SF, the SFF strips the SR segment-list (label 447 stack) from the packet, updates the SR information, and saves it to a 448 cache indexed by the NSH Service Path Identifier (SPI) and the 449 Service Index (SI) decremented by 1. This saved SR information is 450 used to re-encapsulate and forward the packet(s) coming back from the 451 SF. 453 5.2. SR-based SFC (SRv6) Packet Processing 455 This section describes the End.NSH behavior and NSH processing logic 456 for SRv6. The pseudo code is shown below. 458 When N receives a packet destined to S and S is a local End.NSH SID, 459 the processing is the same as that specified by RFC 8754 section 460 4.3.1.1, up through line S.16. 462 After S.15, if S is a local End.NSH SID, then: 464 S15.1. Remove and store IPv6 and SRH headers in local cache indexed 465 by 467 S15.2. Submit the packet to the NSH FIB lookup and transmit to the 468 destination associated with 470 Note: The End.NSH behavior interrupts the normal SRH packet 471 processing as described in RFC8754 section 4.3.1.1, which does not 472 continue to S16 at this time. 474 When a packet is returned to the SFF from the SF, reattach the cached 475 IPv6 and SRH headers based on the from the NSH header. Then resume processing from [RFC8754] 477 section 4.3.1.1 with line S.16. 479 6. Encapsulation 481 6.1. NSH using SR-MPLS Transport 483 SR-MPLS instantiates Segment IDs (SIDs) as MPLS labels and therefore 484 the segment routing header is a stack of MPLS labels. 486 When carrying NSH within an SR-MPLS transport, the full encapsulation 487 headers are as illustrated in Figure 5. 489 +------------------+ 490 ~ MPLS-SR Labels ~ 491 +------------------+ 492 | NSH Base Hdr | 493 +------------------+ 494 | Service Path Hdr | 495 +------------------+ 496 ~ Metadata ~ 497 +------------------+ 499 Figure 5: NSH using SR-MPLS Transport 501 As described in [RFC8402], the IGP signaling extension for IGP-Prefix 502 segment includes a flag to indicate whether directly connected 503 neighbors of the node on which the prefix is attached should perform 504 the NEXT operation or the CONTINUE operation when processing the SID. 505 When NSH is carried beneath SR-MPLS it is necessary to terminate the 506 NSH-based SFC at the tail-end node of the SR-MPLS label stack. This 507 can be achieved using either the NEXT or CONTINUE operation. 509 If NEXT operation is to be used, then at the end of the SR-MPLS path 510 it is necessary to provide an indication to the tail-end that NSH 511 follows the SR-MPLS label stack as described by [RFC8596]. 513 If CONTINUE operation is to be used, this is the equivalent of MPLS 514 Ultimate Hop Popping (UHP) and therefore it is necessary to ensure 515 that the penultimate hop node does not pop the top label of the SR- 516 MPLS label stack and thereby expose NSH to the wrong SFF. This is 517 realized by setting No-PHP flag in Prefix-SID Sub-TLV [RFC8667], 518 [RFC8665]. It is RECOMMENDED that a specific prefix-SID be allocated 519 at each node for use by the SFC application for this purpose. 521 6.2. NSH using SRv6 Transport 523 When carrying NSH within an SRv6 transport the full encapsulation is 524 as illustrated in Figure 6. 526 0 1 2 3 527 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 1 528 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 529 | Next Header | Hdr Ext Len | Routing Type | Segments Left | 530 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 531 | Last Entry | Flags | Tag | S 532 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 533 | | g 534 | Segment List[0] (128 bits IPv6 address) | m 535 | | e 536 | | n 537 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ t 538 | | 539 | | R 540 ~ ... ~ o 541 | | u 542 | | t 543 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ i 544 | | n 545 | Segment List[n] (128 bits IPv6 address) | g 546 | | 547 | | S 548 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ R 549 // // H 550 // Optional Type Length Value objects (variable) // 551 // // 552 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 553 |Ver|O|U| TTL | Length |U|U|U|U|MD Type| Next Protocol | 554 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ N 555 | Service Path Identifier | Service Index | S 556 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ H 557 | | 558 ~ Variable-Length Context Headers (opt.) ~ 559 | | 560 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 562 Figure 6: NSH using SRv6 Transport 564 Encapsulation of NSH following SRv6 is indicated by the IP protocol 565 number for NSH in the Next Header of the SRH. 567 7. Security Considerations 569 Generic SFC-related security considerations are discussed in 570 [RFC7665]. 572 NSH-specific security considerations are discussed in [RFC8300]. 574 Generic segment routing related security considerations are discussed 575 in section 7 of [RFC8754] and section 5 of [RFC8663]. 577 8. MTU Considerations 579 Aligned with Section 5 of [RFC8300] and Section 5.3 of [RFC8754], it 580 is RECOMMENDED for network operators to increase the underlying MTU 581 so that SR/NSH traffic is forwarded within an SR domain without 582 fragmentation. 584 9. IANA Considerations 586 9.1. Protocol Number for NSH 588 IANA is requested to assign a protocol number TBA1 for the NSH from the 589 "Assigned Internet Protocol Numbers" registry available at 590 https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml 592 +---------+---------+--------------+---------------+----------------+ 593 | Decimal | Keyword | Protocol | IPv6 | Reference | 594 | | | | Extension | | 595 | | | | Header | | 596 +---------+---------+--------------+---------------+----------------+ 597 | TBA1 | NSH | Network | N | [ThisDocument] | 598 | | | Service | | | 599 | | | Header | | | 600 +---------+---------+--------------+---------------+----------------+ 602 9.2. SRv6 Endpoint Behavior for NSH 604 This I-D requests IANA to allocate, within the "SRv6 Endpoint Behaviors" 605 sub-registry belonging to the top-level "Segment-routing with IPv6 data 606 plane (SRv6) Parameters" registry, the following allocations: 608 Value Description Reference 609 -------------------------------------------------------------- 610 TBA2 End.NSH - NSH Segment [This.ID] 612 10. Contributing Authors 614 The following co-authors, along with their respective affiliations at 615 the time of WG adoption, provided valuable inputs and text contributions 616 to this document. 618 Mohamed Boucadair 619 Orange 620 mohamed.boucadair@orange.com 622 Joel Halpern 623 Ericsson 624 joel.halpern@ericsson.com 626 Syed Hassan 627 Cisco System, inc. 628 shassan@cisco.com 630 Wim Henderickx 631 Nokia 632 wim.henderickx@nokia.com 634 Haoyu Song 635 Futurewei Technologies 636 haoyu.song@futurewei.com 638 11. References 640 11.1. Normative References 642 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 643 Requirement Levels", BCP 14, RFC 2119, 644 DOI 10.17487/RFC2119, March 1997, 645 . 647 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 648 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 649 January 2012, . 651 [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function 652 Chaining (SFC) Architecture", RFC 7665, 653 DOI 10.17487/RFC7665, October 2015, 654 . 656 [RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE- 657 in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, 658 March 2017, . 660 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 661 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 662 May 2017, . 664 [RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed., 665 "Network Service Header (NSH)", RFC 8300, 666 DOI 10.17487/RFC8300, January 2018, 667 . 669 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 670 Decraene, B., Litkowski, S., and R. Shakir, "Segment 671 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 672 July 2018, . 674 [RFC8596] Malis, A., Bryant, S., Halpern, J., and W. Henderickx, 675 "MPLS Transport Encapsulation for the Service Function 676 Chaining (SFC) Network Service Header (NSH)", RFC 8596, 677 DOI 10.17487/RFC8596, June 2019, 678 . 680 [RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S., 681 Decraene, B., Litkowski, S., and R. Shakir, "Segment 682 Routing with the MPLS Data Plane", RFC 8660, 683 DOI 10.17487/RFC8660, December 2019, 684 . 686 [RFC8663] Xu, X., Bryant, S., Farrel, A., Hassan, S., Henderickx, 687 W., and Z. Li, "MPLS Segment Routing over IP", RFC 8663, 688 DOI 10.17487/RFC8663, December 2019, 689 . 691 [RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler, 692 H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 693 Extensions for Segment Routing", RFC 8665, 694 DOI 10.17487/RFC8665, December 2019, 695 . 697 [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 698 Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 699 Extensions for Segment Routing", RFC 8667, 700 DOI 10.17487/RFC8667, December 2019, 701 . 703 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 704 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 705 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 706 . 708 11.2. Informative References 710 [I-D.ietf-spring-sr-service-programming] 711 Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca, 712 d., Li, C., Decraene, B., Ma, S., Yadlapalli, C., 713 Henderickx, W., and S. Salsano, "Service Programming with 714 Segment Routing", draft-ietf-spring-sr-service- 715 programming-03 (work in progress), September 2020. 717 [RFC7498] Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for 718 Service Function Chaining", RFC 7498, 719 DOI 10.17487/RFC7498, April 2015, 720 . 722 Authors' Addresses 724 James N Guichard (editor) 725 Futurewei Technologies 726 2330 Central Express Way 727 Santa Clara 728 USA 730 Email: james.n.guichard@futurewei.com 732 Jeff Tantsura (editor) 733 Apstra inc. 734 USA 736 Email: jefftant.ietf@gmail.com