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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 639 -- Looks like a reference, but probably isn't: '1' on line 614 Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 6man R. Bonica 3 Internet-Draft Juniper Networks 4 Intended status: Standards Track Y. Kamite 5 Expires: 16 May 2022 NTT Communications Corporation 6 A. Alston 7 D. Henriques 8 Liquid Telecom 9 L. Jalil 10 Verizon 11 12 November 2021 13 The IPv6 Compact Routing Header (CRH) 14 draft-bonica-6man-comp-rtg-hdr-27 16 Abstract 18 This document defines two new Routing header types. Collectively, 19 they are called the Compact Routing Headers (CRH). Individually, 20 they are called CRH-16 and CRH-32. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at https://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on 16 May 2022. 39 Copyright Notice 41 Copyright (c) 2021 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 46 license-info) in effect on the date of publication of this document. 47 Please review these documents carefully, as they describe your rights 48 and restrictions with respect to this document. Code Components 49 extracted from this document must include Simplified BSD License text 50 as described in Section 4.e of the Trust Legal Provisions and are 51 provided without warranty as described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 57 3. The Compressed Routing Headers (CRH) . . . . . . . . . . . . 3 58 4. The CRH Forwarding Information Base (CRH-FIB) . . . . . . . . 4 59 5. Processing Rules . . . . . . . . . . . . . . . . . . . . . . 6 60 5.1. Computing Minimum CRH Length . . . . . . . . . . . . . . 7 61 5.2. CRH Removal Procedure . . . . . . . . . . . . . . . . . . 8 62 6. Mutability . . . . . . . . . . . . . . . . . . . . . . . . . 8 63 7. Applications And SIDs . . . . . . . . . . . . . . . . . . . . 8 64 8. Management Considerations . . . . . . . . . . . . . . . . . . 9 65 9. Security Considerations . . . . . . . . . . . . . . . . . . . 9 66 10. Implementation and Deployment Status . . . . . . . . . . . . 9 67 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 68 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 69 13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 10 70 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 71 14.1. Normative References . . . . . . . . . . . . . . . . . . 11 72 14.2. Informative References . . . . . . . . . . . . . . . . . 11 73 Appendix A. CRH Processing Examples . . . . . . . . . . . . . . 12 74 A.1. The SID List Contains One Entry For Each Segment In The 75 Path . . . . . . . . . . . . . . . . . . . . . . . . . . 13 76 A.2. The SID List Omits The First Entry In The Path . . . . . 14 77 Appendix B. A Packet Recycling Use-Case . . . . . . . . . . . . 14 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 80 1. Introduction 82 IPv6 [RFC8200] source nodes use Routing headers to specify the path 83 that a packet takes to its destination. The IETF has defined several 84 Routing header types [IANA-RH]. This document defines two new 85 Routing header types. Collectively, they are called the Compact 86 Routing Headers (CRH). Individually, they are called CRH-16 and CRH- 87 32. 89 The CRH allows IPv6 source nodes to specify the path that a packet 90 takes to its destination. The CRH: 92 * Can be encoded in relatively few bytes. 94 * Is designed to operate within a network domain. (See Section 9). 96 The following are reasons for encoding the CRH in as few bytes as 97 possible: 99 * Many ASIC-based forwarders copy headers from buffer memory to on- 100 chip memory. As header sizes increase, so does the cost of this 101 copy. 103 * Because Path MTU Discovery (PMTUD) [RFC8201] is not entirely 104 reliable, many IPv6 hosts refrain from sending packets larger than 105 the IPv6 minimum link MTU (i.e., 1280 bytes). When packets are 106 small, the overhead imposed by large Routing Headers is excessive. 108 2. Requirements Language 110 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 111 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 112 "OPTIONAL" in this document are to be interpreted as described in BCP 113 14 [RFC2119] [RFC8174] when, and only when, they appear in all 114 capitals, as shown here. 116 3. The Compressed Routing Headers (CRH) 118 Both CRH versions (i.e., CRH-16 and CRH-32) contain the following 119 fields: 121 * Next Header - Defined in [RFC8200]. 123 * Hdr Ext Len - Defined in [RFC8200]. 125 * Routing Type - Defined in [RFC8200]. Value TBD by IANA. (For 126 CRH-16, the suggested value is 5. For CRH-32, the suggested value 127 is 6.) 129 * Segments Left - Defined in [RFC8200]. 131 * Type-specific Data - Described in [RFC8200]. 133 In the CRH, the Type-specific data field contains a list of Segment 134 Identifiers (SIDs). Each SID represents both of the following: 136 * A segment of the path that the packet takes to its destination. 138 * An entry in the CRH Forwarding Information Base (CRH-FIB) 139 (Section 4). 141 SIDs are listed in reverse order. So, the first SID in the list 142 represents the final segment in the path. Because segments are 143 listed in reverse order, the Segments Left field can be used as an 144 index into the SID list. In this document, the "current SID" is the 145 SID list entry referenced by the Segments Left field. 147 The first segment in the path can be omitted from the list. See 148 Appendix A for examples. 150 In the CRH-16 (Figure 1), each SID is encoded in 16-bits. In the 151 CRH-32 (Figure 2), each SID is encoded in 32-bits. 153 In all cases, the CRH MUST end on a 64-bit boundary. So, the Type- 154 specific data field MUST be padded with zeros if the CRH would 155 otherwise not end on a 64-bit boundary. 157 0 1 2 3 158 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 1 159 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 160 | Next Header | Hdr Ext Len | Routing Type | Segments Left | 161 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 162 | SID[0] | SID[1] | 163 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 164 | ......... 165 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 167 Figure 1: CRH-16 169 0 1 2 3 170 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 1 171 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 172 | Next Header | Hdr Ext Len | Routing Type | Segments Left | 173 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 174 + SID[0] + 175 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 176 + SID[1] + 177 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 178 // // 179 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 180 + SID[n] + 181 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 183 Figure 2: CRH-32 185 4. The CRH Forwarding Information Base (CRH-FIB) 187 Each SID identifies a CRH-FIB entry. 189 Each CRH-FIB entry contains: 191 * An IPv6 address (optional). 193 * A topological function. 195 * Arguments for the topological function (optional). 197 * Flags. 199 * A service function (optional). 201 * Arguments for the service function (optional). 203 The IPv6 address can represent either: 205 * An interface on the next segment endpoint. 207 * An SRv6 SID [RFC8986], instantiated on the next segment endpoint. 209 The first ten bits of the IPv6 address MUST NOT be fe00. That prefix 210 is reserved for link-local [RFC6890] addresses. 212 The topological function specifies how the processing node forwards 213 the packet to the next segment endpoint. The following are examples: 215 * Forward the packet through the least-cost path to the next segment 216 endpoint. 218 * Forward the packet through a specified interface. 220 * Encapsulate the packet in another IPv6 header of any type (e.g., 221 MPLS, IPv6) and forward either through the least cost path or a 222 specified interface. 224 * Recycle the packet, as if the node had forwarded to one of its own 225 interfaces. When recycling is complete, process the next SID. 226 See Appendix B for a packet recycling use-case. 228 Some topological functions require parameters. For example, a 229 topological function might require a parameter that identifies the 230 interface through which the packet should be forwarded. 232 The following flags are defined: 234 * The PSP flag indicates whether the penultimate segment endpoint 235 (i.e., the node that sets Segments Left to 0) MAY remove the CRH. 237 * The OAM flag indicates whether the processing node should invoke 238 OAM procedures for which it is configured. 240 The service function is optional. If present, it invokes a node 241 specific procedure. The following are examples of node specific 242 procedures: 244 * Emit telemetry. 246 * Subject the packet's payload to a firewall rule. 248 * Replicate the packet, forwarding one copy and retaining the other 249 for sampling, analysis, or other purposes. 251 Node specific procedures are not subject to standardization. A node 252 can support any number of node specific procedures and associate them 253 with any SIDs. 255 Some service functions require parameters. For example, an 256 instruction to emit telemetry might require an IP address to which 257 telemetry should be sent. 259 The CRH-FIB can be populated: 261 * By an operator, using a Command Line Interface (CLI). 263 * By a controller, using the Path Computation Element (PCE) 264 Communication Protocol (PCEP) [RFC5440] or the Network 265 Configuration Protocol (NETCONF) [RFC6241]. 267 * By a distributed routing protocol [ISO10589-Second-Edition], 268 [RFC5340], [RFC4271]. 270 5. Processing Rules 272 The following rules describe CRH processing: 274 * If Segments Left equals 0, skip over the CRH and process the next 275 header in the packet. 277 * If Hdr Ext Len indicates that the CRH is larger than the 278 implementation can process, discard the packet and send an ICMPv6 279 [RFC4443] Parameter Problem, Code 0, message to the Source 280 Address, pointing to the Hdr Ext Len field. 282 * Compute L, the minimum CRH length ( Section 5.1). 284 * If L is greater than Hdr Ext Len, discard the packet and send an 285 ICMPv6 Parameter Problem, Code 0, message to the Source Address, 286 pointing to the Segments Left field. 288 * Decrement Segments Left. 290 * Search for the current SID in the CRH-FIB. In this document, the 291 "current SID" is the SID list entry referenced by the Segments 292 Left field. 294 * If the search does not return a CRH-FIB entry, discard the packet 295 and send an ICMPv6 Parameter Problem, Code 0, message to the 296 Source Address, pointing to the current SID. 298 * If Segments Left is greater than 0 and the CRH-FIB entry contains 299 a multicast address, discard the packet and send an ICMPv6 300 Parameter Problem, Code 0, message to the Source Address, pointing 301 to the current SID. 303 * If present, copy the IPv6 address from the CRH-FIB entry to the 304 Destination Address field in the IPv6 header. 306 * Decrement the IPv6 Hop Limit. 308 * If the CRH-FIB entry contains a service function, execute it. 310 * If Segments Left is equal to zero, and the PSP flag in the CRH-FIB 311 entry is set, execute the CRH removal procedure ( Section 5.2). 313 * Submit the packet, its topological function and its parameters to 314 the IPv6 module. See NOTE. 316 NOTE: By default, the IPv6 module determines the next-hop and 317 forwards the packet. However, the topological function may elicit 318 another behavior. For example, the IPv6 module may forward the 319 packet through a specified interface. 321 5.1. Computing Minimum CRH Length 323 The algorithm described in this section accepts the following CRH 324 fields as its input parameters: 326 * Routing Type (i.e., CRH-16 or CRH-32). 328 * Segments Left. 330 It yields L, the minimum CRH length. The minimum CRH length is 331 measured in 8-octet units, not including the first 8 octets. 333 334 switch(Routing Type) { 335 case CRH-16: 336 if (Segments Left <= 2) 337 return(0) 338 sidsBeyondFirstWord = Segments Left - 2; 339 sidPerWord = 4; 340 case CRH-32: 341 if (Segments Left <= 1) 342 return(0) 343 sidsBeyondFirstWord = Segments Left - 1; 344 sidsPerWord = 2; 345 case default: 346 return(0xFF); 347 } 349 words = sidsBeyondFirstWord div sidsPerWord; 350 if (sidsBeyondFirstWord mod sidsPerWord) 351 words++; 353 return(words) 354 356 5.2. CRH Removal Procedure 358 The processing node SHOULD execute the following procedure, if it is 359 capable of doing so: 361 * Update the Next Header field in the header preceding the CRH using 362 a value taken from the Next Header field in the CRH. 364 * Decrease the Payload Length filed in the IPv6 header by 8*(x+1), 365 where value of x is equal to the value of the Hdr Ext Len field in 366 the CRH. 368 * Remove the CRH from the IPv6 header chain. 370 6. Mutability 372 In the CRH, the Segments Left field is mutable. All remaining fields 373 are immutable. 375 7. Applications And SIDs 377 A CRH contains one or more SIDs. Each SID is processed by exactly 378 one node. 380 Therefore, a SID is not required to have domain-wide significance. 381 Applications can: 383 * Allocate SIDs so that they have domain-wide significance. 385 * Allocate SIDs so that they have node-local significance. 387 8. Management Considerations 389 PING and TRACEROUTE [RFC2151] both operate correctly in the presence 390 of the CRH. 392 9. Security Considerations 394 Networks that process the CRH MUST NOT accept packets containing the 395 CRH from untrusted sources. Their border routers SHOULD discard 396 packets that satisfy the following criteria: 398 * The packet contains a CRH 400 * The Segments Left field in the CRH has a value greater than 0 402 * The Destination Address field in the IPv6 header represents an 403 interface that resides inside of the network. 405 Many border routers cannot filter packets based upon the Segments 406 Left value. These border routers MAY discard packets that satisfy 407 the following criteria: 409 * The packet contains a CRH 411 * The Destination Address field in the IPv6 header represents an 412 interface that resides inside of the network. 414 10. Implementation and Deployment Status 416 Juniper Networks has produced experimental implementations of the CRH 417 on: 419 * A LINUX-based software platform 421 * The MX-series (ASIC-based) router 423 Liquid Telecom has deployed the CRH, on a limited basis, in their 424 network. Other experimental deployments are in progress. 426 11. IANA Considerations 428 This document makes the following registrations in the "Internet 429 Protocol Version 6 (IPv6) Parameters" "Routing Types" subregistry 430 maintained by IANA: 432 +-------+------------------------------+---------------+ 433 | Value | Description | Reference | 434 +=======+==============================+===============+ 435 | 5 | CRH-16 | This document | 436 +-------+------------------------------+---------------+ 437 | 6 | CRH-32 | This document | 438 +-------+------------------------------+---------------+ 440 12. Acknowledgements 442 Thanks to Dr. Vanessa Ameen, Fernando Gont, Naveen Kottapalli, Joel 443 Halpern, Tony Li, Gerald Schmidt, Nancy Shaw, Ketan Talaulikar, and 444 Chandra Venkatraman for their contributions to this document. 446 13. Contributors 448 Gang Chen 450 Baidu 452 No.10 Xibeiwang East Road Haidian District 454 Beijing 100193 P.R. China 456 Email: phdgang@gmail.com 458 Yifeng Zhou 460 ByteDance 462 Building 1, AVIC Plaza, 43 N 3rd Ring W Rd Haidian District 464 Beijing 100000 P.R. China 466 Email: yifeng.zhou@bytedance.com 468 Gyan Mishra 470 Verizon 471 Silver Spring, Maryland, USA 473 Email: hayabusagsm@gmail.com 475 14. References 477 14.1. Normative References 479 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 480 Requirement Levels", BCP 14, RFC 2119, 481 DOI 10.17487/RFC2119, March 1997, 482 . 484 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 485 Control Message Protocol (ICMPv6) for the Internet 486 Protocol Version 6 (IPv6) Specification", STD 89, 487 RFC 4443, DOI 10.17487/RFC4443, March 2006, 488 . 490 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 491 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 492 May 2017, . 494 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 495 (IPv6) Specification", STD 86, RFC 8200, 496 DOI 10.17487/RFC8200, July 2017, 497 . 499 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 500 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 501 DOI 10.17487/RFC8201, July 2017, 502 . 504 14.2. Informative References 506 [IANA-RH] IANA, "Routing Headers", 507 . 510 [ISO10589-Second-Edition] 511 International Organization for Standardization, 512 ""Intermediate system to Intermediate system intra-domain 513 routeing information exchange protocol for use in 514 conjunction with the protocol for providing the 515 connectionless-mode Network Service (ISO 8473)", ISO/IEC 516 10589:2002, Second Edition,", November 2001. 518 [RFC2151] Kessler, G. and S. Shepard, "A Primer On Internet and TCP/ 519 IP Tools and Utilities", FYI 30, RFC 2151, 520 DOI 10.17487/RFC2151, June 1997, 521 . 523 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 524 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 525 DOI 10.17487/RFC4271, January 2006, 526 . 528 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 529 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 530 . 532 [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation 533 Element (PCE) Communication Protocol (PCEP)", RFC 5440, 534 DOI 10.17487/RFC5440, March 2009, 535 . 537 [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., 538 and A. Bierman, Ed., "Network Configuration Protocol 539 (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, 540 . 542 [RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman, 543 "Special-Purpose IP Address Registries", BCP 153, 544 RFC 6890, DOI 10.17487/RFC6890, April 2013, 545 . 547 [RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer, 548 D., Matsushima, S., and Z. Li, "Segment Routing over IPv6 549 (SRv6) Network Programming", RFC 8986, 550 DOI 10.17487/RFC8986, February 2021, 551 . 553 Appendix A. CRH Processing Examples 555 This appendix demonstrates CRH processing in the following scenarios: 557 * The SID list contains one entry for each segment in the path 558 (Appendix A.1). 560 * The SID list omits the first entry in the path (Appendix A.2). 562 ----------- ----------- ----------- 563 |Node: S | |Node: I1 | |Node: I2 | 564 |Loopback: |---------------|Loopback: |---------------|Loopback: | 565 |2001:db8::a| |2001:db8::1| |2001:db8::2| 566 ----------- ----------- ----------- 567 | | 568 | ----------- | 569 | |Node: D | | 570 ---------------------|Loopback: |--------------------- 571 |2001:db8::b| 572 ----------- 574 Figure 3: Reference Topology 576 Figure 3 provides a reference topology that is used in all examples. 578 +=====+==============+===================+ 579 | SID | IPv6 Address | Forwarding Method | 580 +=====+==============+===================+ 581 | 2 | 2001:db8::2 | Least-cost path | 582 +-----+--------------+-------------------+ 583 | 11 | 2001:db8::b | Least-cost path | 584 +-----+--------------+-------------------+ 586 Table 1: Node SIDs 588 Table 1 describes two entries that appear in each node's CRH-FIB. 590 A.1. The SID List Contains One Entry For Each Segment In The Path 592 In this example, Node S sends a packet to Node D, via I2. In this 593 example, I2 appears in the CRH segment list. 595 +=====================================+===================+ 596 | As the packet travels from S to I2: | | 597 +=====================================+===================+ 598 | Source Address = 2001:db8::a | Segments Left = 1 | 599 +-------------------------------------+-------------------+ 600 | Destination Address = 2001:db8::2 | SID[0] = 11 | 601 +-------------------------------------+-------------------+ 602 | | SID[1] = 2 | 603 +-------------------------------------+-------------------+ 605 Table 2 607 +=====================================+===================+ 608 | As the packet travels from I2 to D: | | 609 +=====================================+===================+ 610 | Source Address = 2001:db8::a | Segments Left = 0 | 611 +-------------------------------------+-------------------+ 612 | Destination Address = 2001:db8::b | SID[0] = 11 | 613 +-------------------------------------+-------------------+ 614 | | SID[1] = 2 | 615 +-------------------------------------+-------------------+ 617 Table 3 619 A.2. The SID List Omits The First Entry In The Path 621 In this example, Node S sends a packet to Node D, via I2. In this 622 example, I2 does not appear in the CRH segment list. 624 +=====================================+===================+ 625 | As the packet travels from S to I2: | | 626 +=====================================+===================+ 627 | Source Address = 2001:db8::a | Segments Left = 1 | 628 +-------------------------------------+-------------------+ 629 | Destination Address = 2001:db8::2 | SID[0] = 11 | 630 +-------------------------------------+-------------------+ 632 Table 4 634 +=====================================+===================+ 635 | As the packet travels from I2 to D: | | 636 +=====================================+===================+ 637 | Source Address = 2001:db8::a | Segments Left = 0 | 638 +-------------------------------------+-------------------+ 639 | Destination Address = 2001:db8::b | SID[0] = 11 | 640 +-------------------------------------+-------------------+ 642 Table 5 644 Appendix B. A Packet Recycling Use-Case 645 Network A--D1 646 / \ / 647 / \ / 648 / \ / 649 S ---- P + 650 \ / \ 651 \ / \ 652 \ / \ 653 Network B---DN 655 Figure 4: Packet Recycling Use-case 657 In Figure 4: 659 * The SR domain contains Node S, Node P, and a set of destination 660 nodes (D1 through DN) 662 * S is connected to P 664 * P is connected to Network A and to Network B. Neither of these 665 networks are SR-capable. 667 * The destination nodes connect to both Network A and Network B 669 S needs to reach each destination node through two SR paths. One SR 670 path traverses Network A while the other traverses Network B. 672 Uncompressed SRv6 can encode this SR Path in two segments,with one 673 segment instantiated on P and the other on the destination. To 674 support this strategy, P instantiates two END.X SIDs (one per 675 network). 677 CRH compressed SRv6 can encode this SR Path in two or three segments. 678 When it encodes the path in two segments, one segment instantiated on 679 P and the other on the destination. To support this strategy, P 680 instantiates 2*N SIDs (one per network per destination). When CRH 681 compressed SRv6 encodes the path in three segments, two segments are 682 instantiated on P and the other on the destination. The first 683 segment on P updates the IPv6 Destination address without forwarding 684 the packet, while the other segment on P forwards the packet without 685 updating the IPv6 destination address. To support this strategy, P 686 instantiates 2+N SIDs (one per network and one per destination). 688 Authors' Addresses 690 Ron Bonica 691 Juniper Networks 692 2251 Corporate Park Drive 693 Herndon, Virginia 20171 694 United States of America 696 Email: rbonica@juniper.net 698 Yuji Kamite 699 NTT Communications Corporation 700 3-4-1 Shibaura, Minato-ku, 701 108-8118 702 Japan 704 Email: y.kamite@ntt.com 706 Andrew Alston 707 Liquid Telecom 708 Nairobi 709 Kenya 711 Email: Andrew.Alston@liquidtelecom.com 713 Daniam Henriques 714 Liquid Telecom 715 Johannesburg 716 South Africa 718 Email: daniam.henriques@liquidtelecom.com 720 Luay Jalil 721 Verizon 722 Richardson, Texas 723 United States of America 725 Email: luay.jalil@one.verizon.com