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Filsfils 4 Intended status: Standards Track Cisco Systems 5 Expires: January 14, 2021 S. Matsushima 6 Softbank 7 D. Voyer 8 Bell Canada 9 M. Chen 10 Huawei 11 July 13, 2020 13 Operations, Administration, and Maintenance (OAM) in Segment Routing 14 Networks with IPv6 Data plane (SRv6) 15 draft-ietf-6man-spring-srv6-oam-06 17 Abstract 19 This document describes how the existing IPv6 OAM mechanisms can be 20 used in an SRv6 network. The document also introduces enhancements 21 for OAM mechanisms for SRv6 networks. 23 Status of This Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at https://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on January 14, 2021. 40 Copyright Notice 42 Copyright (c) 2020 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (https://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 58 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 59 1.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 3 60 1.3. Terminology and Reference Topology . . . . . . . . . . . 3 61 2. OAM Mechanisms . . . . . . . . . . . . . . . . . . . . . . . 5 62 2.1. O-flag in Segment Routing Header . . . . . . . . . . . . 5 63 2.1.1. O-flag Processing . . . . . . . . . . . . . . . . . . 5 64 2.2. OAM Operations . . . . . . . . . . . . . . . . . . . . . 7 65 3. Illustrations . . . . . . . . . . . . . . . . . . . . . . . . 7 66 3.1. Ping in SRv6 Networks . . . . . . . . . . . . . . . . . . 8 67 3.1.1. Classic Ping . . . . . . . . . . . . . . . . . . . . 8 68 3.1.2. Pinging a SID . . . . . . . . . . . . . . . . . . . . 9 69 3.2. Traceroute . . . . . . . . . . . . . . . . . . . . . . . 10 70 3.2.1. Classic Traceroute . . . . . . . . . . . . . . . . . 10 71 3.2.2. Traceroute to a SID . . . . . . . . . . . . . . . . . 12 72 3.3. A Hybrid OAM Using O-flag . . . . . . . . . . . . . . . . 13 73 3.4. Monitoring of SRv6 Paths . . . . . . . . . . . . . . . . 16 74 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 17 75 5. Security Considerations . . . . . . . . . . . . . . . . . . . 17 76 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 77 6.1. Segment Routing Header Flags . . . . . . . . . . . . . . 17 78 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18 79 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 18 80 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 81 9.1. Normative References . . . . . . . . . . . . . . . . . . 19 82 9.2. Informative References . . . . . . . . . . . . . . . . . 19 83 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 85 1. Introduction 87 As Segment Routing with IPv6 data plane (SRv6) [RFC8402] simply adds 88 a new type of Routing Extension Header, existing IPv6 OAM mechanisms 89 can be used in an SRv6 network. This document describes how the 90 existing IPv6 mechanisms for ping and trace route can be used in an 91 SRv6 network. 93 The document also introduces enhancements for OAM mechanism for SRv6 94 networks. Specifically, the document describes an OAM mechanism for 95 performing controllable and predictable flow sampling from segment 96 endpoints using, e.g., IP Flow Information Export (IPFIX) protocol 98 [RFC7011]. The document also outlines how centralized OAM technique 99 in [RFC8403] can be extended for SRv6 to perform a path continuity 100 check between any nodes within an SRv6 domain from a centralized 101 monitoring system. 103 1.1. Requirements Language 105 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 106 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 107 document are to be interpreted as described in [RFC2119], [RFC8174]. 109 1.2. Abbreviations 111 The following abbreviations are used in this document: 113 SID: Segment ID. 115 SL: Segments Left. 117 SR: Segment Routing. 119 SRH: Segment Routing Header [RFC8754]. 121 SRv6: Segment Routing with IPv6 Data plane. 123 TC: Traffic Class. 125 ICMPv6: ICMPv6 Specification [RFC4443]. 127 1.3. Terminology and Reference Topology 129 Throughout the document, the following terminology and simple 130 topology is used for illustration. 132 +--------------------------| N100 |---------------------------------+ 133 | | 134 | ====== link1====== link3------ link5====== link9------ ====== | 135 ||N1||------||N2||------| N3 |------||N4||------| N5 |---||N7|| 136 || ||------|| ||------| |------|| ||------| |---|| || 137 ====== link2====== link4------ link6======link10------ ====== 138 | | | | 139 ---+-- | ------ | --+--- 140 |CE 1| +-------| N6 |---------+ |CE 2| 141 ------ link7 | | link8 ------ 142 ------ 144 Figure 1 Reference Topology 146 In the reference topology: 148 Node k has a classic IPv6 loopback address 2001:DB8:A:k::/128. 150 Nodes N1, N2, N4 and N7 are SRv6 capable nodes. 152 Nodes N3, N5 and N6 are IPv6 nodes that are not SRv6 capable. 153 Such nodes are referred as classic IPv6 nodes. 155 CE1 and CE2 are Customer Edge devices of any data plane capability 156 (e.g., IPv4, IPv6, L2, etc.). 158 A SID at node k with locator block 2001:DB8:B::/48 and function F 159 is represented by 2001:DB8:B:k:F::. 161 Node N100 is a controller. 163 The IPv6 address of the nth Link between node X and Y at the X 164 side is represented as 2001:DB8:X:Y:Xn::, e.g., the IPv6 address 165 of link6 (the 2nd link) between N3 and N4 at N3 in Figure 1 is 166 2001:DB8:3:4:32::. Similarly, the IPv6 address of link5 (the 1st 167 link between N3 and N4) at node 3 is 2001:DB8:3:4:31::. 169 2001:DB8:B:k:Cij:: is explicitly allocated as the END.X SID (refer 170 [I-D.ietf-spring-srv6-network-programming]) at node k towards 171 neighbor node i via jth Link between node i and node k. e.g., 172 2001:DB8:B:2:C31:: represents END.X at N2 towards N3 via link3 173 (the 1st link between N2 and N3). Similarly, 2001:DB8:B:4:C52:: 174 represents the END.X at N4 towards N5 via link10. 176 A SID list is represented as where S1 is the first 177 SID to visit, S2 is the second SID to visit and S3 is the last SID 178 to visit along the SR path. 180 (SA,DA) (S3, S2, S1; SL)(payload) represents an IPv6 packet with: 182 * IPv6 header with source address SA, destination addresses DA 183 and SRH as next-header 185 * SRH with SID list with SegmentsLeft = SL 187 * Note the difference between the < > and () symbols: represents a SID list where S1 is the first SID and S3 is 189 the last SID to traverse. (S3, S2, S1; SL) represents the same 190 SID list but encoded in the SRH format where the rightmost SID 191 in the SRH is the first SID and the leftmost SID in the SRH is 192 the last SID. When referring to an SR policy in a high-level 193 use-case, it is simpler to use the notation. When 194 referring to an illustration of the detailed packet behavior, 195 the (S3, S2, S1; SL) notation is more convenient. 197 * (payload) represents the the payload of the packet. 199 SRH[SL] represents the SID pointed by the SL field in the first 200 SRH. In our example SID list (S3, S2, S1; SL), SRH[2] represents 201 S1, SRH[1] represents S2 and SRH[0] represents S3. 203 2. OAM Mechanisms 205 This section defines OAM enhancement for the SRv6 networks. 207 2.1. O-flag in Segment Routing Header 209 [RFC8754] describes the Segment Routing Header (SRH) and how SR 210 capable nodes use it. The SRH contains an 8-bit "Flags" field. This 211 document defines the following bit in the SRH.Flags to carry the 212 O-flag: 214 0 1 2 3 4 5 6 7 215 +-+-+-+-+-+-+-+-+ 216 | |O| | 217 +-+-+-+-+-+-+-+-+ 219 Where: 221 O-flag: OAM flag. 223 The document does not define any other flag in the SRH.Flags and 224 meaning and processing of any other bit in SRH.Flags is outside of 225 the scope of this document. 227 2.1.1. O-flag Processing 229 The O-flag in SRH is used as a marking-bit in the user packets to 230 trigger the telemetry data collection and export at the segment 231 endpoints. 233 This document does not specify the data elements that needs to be 234 exported and the associated configurations. Similarly, this document 235 does not define any formats for exporting the data elements. 236 Nonetheless, without the loss of generality, this document assumes IP 237 Flow Information Export (IPFIX) protocol [RFC7011] is used for 238 exporting the traffic flow information from the network devices to a 239 controller for monitoring and analytics. Similarly, without the loss 240 of generality, this document assumes requested information elements 241 are configured by the management plane through data set templates 242 (e.g., as in IPFIX [RFC7012]). 244 Implementation of the O-flag is OPTIONAL. If a node does not support 245 the O-flag, then upon reception it simply ignores it. If a node 246 supports the O-flag, it can optionally advertise its potential via 247 control plan protocol(s). 249 When N receives a packet whose IPv6 DA is S and S is a local SID, the 250 line S01 of the pseudo-code associated with the SID S, as defined in 251 section 4.3.1.1 of [RFC8754], is modified as follows for the O-flag 252 processing. 254 S01.1. IF SRH.Flags.O-flag is set and local configuration permits 255 O-flag processing THEN 256 a. Make a copy of the packet. 257 b. Send the copied packet, along with a timestamp 258 to the OAM process for telemetry data collection 259 and export. ;; Ref1 260 Ref1: An implementation SHOULD copy and record the timestamp as 261 soon as possible during packet processing. Timestamp or any other 262 metadata is not 263 carried in the packet forwarded to the next hop. 265 Please note that the O-flag processing happens before execution of 266 regular processing of the local SID S. 268 Based on the requested information elements configured by the 269 management plane through data set templates [RFC7012], the OAM 270 process exports the requested information elements. The information 271 elements include parts of the packet header and/or parts of the 272 packet payload for flow identification. The OAM process uses 273 information elements defined in IPFIX [RFC7011] and PSAMP [RFC5476] 274 for exporting the requested sections of the mirrored packets. 276 If the telemetry data from the last node in the segment-list (egress 277 node) is desired, the ingress uses an Ultimate Segment Pop (USP) SID 278 advertised by the egress node. 280 The processing node SHOULD rate-limit the number of packets punted to 281 the OAM process to avoid hitting any performance impact. 283 The OAM process MUST NOT process the copy of the packet or respond to 284 any upper-layer header (like ICMP, UDP, etc.) payload to prevent 285 multiple evaluations of the datagram. 287 Specification of the OAM process or the external controller 288 operations are beyond the scope of this document. How to correlate 289 the data collected from different nodes at an external controller is 290 also outside the scope of the document. Section 3 illustrates use of 291 the SRH.Flags.O-flag for implementing a hybrid OAM mechanism, where 292 the "hybrid" classification is based on RFC7799 [RFC7799]. 294 2.2. OAM Operations 296 IPv6 OAM operations can be performed for any SRv6 SID whose behavior 297 allows Upper Layer Header processing for an applicable OAM payload 298 (e.g., ICMP, UDP). 300 Ping to a SID is used for SID connectivity checks and to validate the 301 availability of a SID. Traceroute to a SID is used for hop-by-hop 302 fault localization as well as path tracing to a SID. Section 3 303 illustrates the ICMPv6 based ping and the UDP based traceroute 304 mechanisms for ping and traceroute to an SRv6 SID. Although this 305 document only illustrates ICMP ping and UDP-based traceroute to an 306 SRv6 SID, the procedures are equally applicable to other IPv6 OAM 307 probing to an SRv6 SID (e.g., Bidirectional Forwarding Detection 308 (BFD) [RFC5880], Seamless BFD (SBFD) [RFC7880], Two-Way Active 309 Measurement Protocol (TWAMP) [RFC5357], Simple Two-Way Active 310 Measurement Protocol (STAMP) [RFC8762], etc.). Specifically, as long 311 as local configuration allows the Upper-layer Header processing of 312 the applicable OAM payload for SRv6 SIDs, the existing IPv6 OAM 313 techniques can be used to target a probe to a (remote) SID. 315 IPv6 OAM operations can be performed with the target SID in the IPv6 316 destination address without SRH or with SRH where the target SID is 317 the last segment. In general, OAM operations to a target SID may not 318 exercise all of its processing depending on its behavior definition. 319 For example, ping to an END.X SID (refer [I-D.ietf-spring-srv6- 320 network-programming]) at the target node only validates availability 321 of the SID and does not validate switching to the correct outgoing 322 interface. To exercise the behavior of a target SID, the OAM 323 operation SHOULD construct the probe in a manner similar to a data 324 packet that exercises the SID behavior, i.e. to include that SID as a 325 transit SID in either an SRH or IPv6 DA of an outer IPv6 header or as 326 appropriate based on the definition of the SID behavior. 328 3. Illustrations 330 This section shows how some of the existing IPv6 OAM mechanisms can 331 be used in an SRv6 network. It also illustrates an OAM mechanism for 332 performing controllable and predictable flow sampling from segment 333 endpoints. How centralized OAM technique in [RFC8403] can be 334 extended for SRv6 is also described in this Section. 336 3.1. Ping in SRv6 Networks 338 The following subsections outline some use cases of the ICMP ping in 339 the SRv6 networks. 341 3.1.1. Classic Ping 343 The existing mechanism to perform the connectivity checks, along the 344 shortest path, continues to work without any modification. The 345 initiator may be an SRv6 node or a classic IPv6 node. Similarly, the 346 egress or transit may be an SRv6 capable node or a classic IPv6 node. 348 If an SRv6 capable ingress node wants to ping an IPv6 address via an 349 arbitrary segment list , it needs to initiate ICMPv6 ping 350 with an SR header containing the SID list . This is 351 illustrated using the topology in Figure 1. Assume all the links 352 have IGP metric 10 except both links between node2 and node3, which 353 have IGP metric set to 100. User issues a ping from node N1 to a 354 loopback of node 5, via segment list <2001:DB8:B:2:C31::, 355 2001:DB8:B:4:C52::>. The SID behavior used in the example is End.X 356 SID (refer [I-D.ietf-spring-srv6-network-programming]) but the 357 procedure is equally applicable to any other (transit) SID type. 359 Figure 2 contains sample output for a ping request initiated at node 360 N1 to the loopback address of node N5 via a segment list 361 <2001:DB8:B:2:C31::, 2001:DB8:B:4:C52::>. 363 > ping 2001:DB8:A:5:: via segment-list 2001:DB8:B:2:C31::, 364 2001:DB8:B:4:C52:: 366 Sending 5, 100-byte ICMP Echos to B5::, timeout is 2 seconds: 367 !!!!! 368 Success rate is 100 percent (5/5), round-trip min/avg/max = 0.625 369 /0.749/0.931 ms 371 Figure 2 A sample ping output at an SRv6 capable node 373 All transit nodes process the echo request message like any other 374 data packet carrying SR header and hence do not require any change. 375 Similarly, the egress node (IPv6 classic or SRv6 capable) does not 376 require any change to process the ICMPv6 echo request. For example, 377 in the ping example of Figure 2: 379 o Node N1 initiates an ICMPv6 ping packet with SRH as follows 380 (2001:DB8:A:1::, 2001:DB8:B:2:C31::) (2001:DB8:A:5::, 381 2001:DB8:B:4:C52::, 2001:DB8:B:2:C31::, SL=2, NH = ICMPv6)(ICMPv6 382 Echo Request). 384 o Node N2, which is an SRv6 capable node, performs the standard SRH 385 processing. Specifically, it executes the END.X behavior 386 (2001:DB8:B:2:C31::) and forwards the packet on link3 to N3. 388 o Node N3, which is a classic IPv6 node, performs the standard IPv6 389 processing. Specifically, it forwards the echo request based on 390 the DA 2001:DB8:B:4:C52:: in the IPv6 header. 392 o Node N4, which is an SRv6 capable node, performs the standard SRH 393 processing. Specifically, it observes the END.X behavior 394 (2001:DB8:B:4:C52::) and forwards the packet on link10 towards N5. 395 If 2001:DB8:B:4:C52:: is a PSP SID, The penultimate node (Node N4) 396 does not, should not and cannot differentiate between the data 397 packets and OAM probes. Specifically, if 2001:DB8:B:4:C52:: is a 398 PSP SID, node N4 executes the SID like any other data packet with 399 DA = 2001:DB8:B:4:C52:: and removes the SRH. 401 o The echo request packet at N5 arrives as an IPv6 packet with or 402 without an SRH. If N5 receives the packet with SRH, it skips SRH 403 processing (SL=0). In either case, Node N5 performs the standard 404 IPv6/ ICMPv6 processing on the echo request. 406 3.1.2. Pinging a SID 408 The classic ping described in the previous section applies equally to 409 perform SID connectivity checks and to validate the availability of a 410 remote SID. This is explained using an example in the following. 411 The example uses ping to an END SID (refer [I-D.ietf-spring-srv6- 412 network-programming]) but the procedure is equally applicable to ping 413 any other SID behaviors. 415 Consider the example where the user wants to ping a remote SID 416 2001:DB8:B:4::, via 2001:DB8:B:2:C31::, from node N1. The ICMPv6 417 echo request is processed at the individual nodes along the path as 418 follows: 420 o Node N1 initiates an ICMPv6 ping packet with SRH as follows 421 (2001:DB8:A:1::, 2001:DB8:B:2:C31::) (2001:DB8:B:4::, 422 2001:DB8:B:2:C31::; SL=1; NH=ICMPv6)(ICMPv6 Echo Request). 424 o Node N2, which is an SRv6 capable node, performs the standard SRH 425 processing. Specifically, it executes the END.X behavior 426 (2001:DB8:B:2:C31::) on the echo request packet. If 427 2001:DB8:B:2:C31:: is a PSP SID, node N4 executes the SID like any 428 other data packet with DA = 2001:DB8:B:2:C31:: and removes the 429 SRH. 431 o Node N3, which is a classic IPv6 node, performs the standard IPv6 432 processing. Specifically, it forwards the echo request based on 433 DA = 2001:DB8:B:4:: in the IPv6 header. 435 o When node N4 receives the packet, it processes the target SID 436 (2001:DB8:B:4::). 438 o If the target SID (2001:DB8:B:4::) is not locally instantiated, 439 the packet is discarded 441 o If the target SID (2001:DB8:B:4::) is locally instantiated, the 442 node processes the upper layer header. As part of the upper layer 443 header processing node N4 respond to the ICMPv6 echo request 444 message. 446 3.2. Traceroute 448 There is no hardware or software change required for traceroute 449 operation at the classic IPv6 nodes in an SRv6 network. That 450 includes the classic IPv6 node with ingress, egress or transit roles. 451 Furthermore, no protocol changes are required to the standard 452 traceroute operations. In other words, existing traceroute 453 mechanisms work seamlessly in the SRv6 networks. 455 The following subsections outline some use cases of the traceroute in 456 the SRv6 networks. 458 3.2.1. Classic Traceroute 460 The existing mechanism to traceroute a remote IP address, along the 461 shortest path, continues to work without any modification. The 462 initiator may be an SRv6 node or a classic IPv6 node. Similarly, the 463 egress or transit may be an SRv6 node or a classic IPv6 node. 465 If an SRv6 capable ingress node wants to traceroute to IPv6 address 466 via an arbitrary segment list , it needs to initiate 467 traceroute probe with an SR header containing the SID list . That is illustrated using the topology in Figure 1. Assume all 469 the links have IGP metric 10 except both links between node2 and 470 node3, which have IGP metric set to 100. User issues a traceroute 471 from node N1 to a loopback of node 5, via segment list 472 <2001:DB8:B:2:C31::, 2001:DB8:B:4:C52::>. The SID behavior used in 473 the example is End.X SID (refer [I-D.ietf-spring-srv6-network- 474 programming]) but the procedure is equally applicable to any other 475 (transit) SID type. Figure 3 contains sample output for the 476 traceroute request. 478 > traceroute 2001:DB8:A:5:: via segment-list 2001:DB8:B:2:C31::, 479 2001:DB8:B:4:C52:: 481 Tracing the route to 2001:DB8:A:5:: 482 1 2001:DB8:1:2:21:: 0.512 msec 0.425 msec 0.374 msec 483 DA: 2001:DB8:B:2:C31::, 484 SRH:(2001:DB8:A:5::, 2001:DB8:B:4:C52::, 2001:DB8:B:2:C31::, SL=2) 485 2 2001:DB8:2:3:31:: 0.721 msec 0.810 msec 0.795 msec 486 DA: 2001:DB8:B:4:C52::, 487 SRH:(2001:DB8:A:5::, 2001:DB8:B:4:C52::, 2001:DB8:B:2:C31::, SL=1) 488 3 2001:DB8:3:4::41:: 0.921 msec 0.816 msec 0.759 msec 489 DA: 2001:DB8:B:4:C52::, 490 SRH:(2001:DB8:A:5::, 2001:DB8:B:4:C52::, 2001:DB8:B:2:C31::, SL=1) 491 4 2001:DB8:4:5::52:: 0.879 msec 0.916 msec 1.024 msec 492 DA: 2001:DB8:A:5:: 494 Figure 3 A sample traceroute output at an SRv6 capable node 496 Please note that information for hop2 is returned by N3, which is a 497 classic IPv6 node. Nonetheless, the ingress node is able to display 498 SR header contents as the packet travels through the IPv6 classic 499 node. This is because the "Time Exceeded Message" ICMPv6 message can 500 contain as much of the invoking packet as possible without the ICMPv6 501 packet exceeding the minimum IPv6 MTU [RFC4443]. The SR header is 502 also included in these ICMPv6 messages initiated by the classic IPv6 503 transit nodes that are not running SRv6 software. Specifically, a 504 node generating ICMPv6 message containing a copy of the invoking 505 packet does not need to understand the extension header(s) in the 506 invoking packet. 508 The segment list information returned for hop1 is returned by N2, 509 which is an SRv6 capable node. Just like for hop2, the ingress node 510 is able to display SR header contents for hop1. 512 There is no difference in processing of the traceroute probe at an 513 IPv6 classic node and an SRv6 capable node. Similarly, both IPv6 514 classic and SRv6 capable nodes may use the address of the interface 515 on which probe was received as the source address in the ICMPv6 516 response. ICMP extensions defined in [RFC5837] can be used to also 517 display information about the IP interface through which the datagram 518 would have been forwarded had it been forwardable, and the IP next 519 hop to which the datagram would have been forwarded, the IP interface 520 upon which a datagram arrived, the sub-IP component of an IP 521 interface upon which a datagram arrived. 523 The information about the IP address of the incoming interface on 524 which the traceroute probe was received by the reporting node is very 525 useful. This information can also be used to verify if SIDs 526 2001:DB8:B:2:C31:: and 2001:DB8:B:4:C52:: are executed correctly by 527 N2 and N4, respectively. Specifically, the information displayed for 528 hop2 contains the incoming interface address 2001:DB8:2:3:31:: at N3. 529 This matches with the expected interface bound to END.X behavior 530 2001:DB8:B:2:C31:: (link3). Similarly, the information displayed for 531 hop5 contains the incoming interface address 2001:DB8:4:5::52:: at 532 N5. This matches with the expected interface bound to the END.X 533 behavior 2001:DB8:B:4:C52:: (link10). 535 3.2.2. Traceroute to a SID 537 The classic traceroute described in the previous section applies 538 equally to traceroute a remote SID behavior, as explained using an 539 example in the following. The example uses traceroute to an END SID 540 (refer [I-D.ietf-spring-srv6-network-programming]) but the procedure 541 is equally applicable to tracerouting any other SID behaviors. 543 Please note that traceroute to a SID is exemplified using UDP probes. 544 However, the procedure is equally applicable to other implementations 545 of traceroute mechanism. 547 Consider the example where the user wants to traceroute a remote SID 548 2001:DB8:B:4::, via 2001:DB8:B:2:C31::, from node N1. The traceroute 549 probe is processed at the individual nodes along the path as follows: 551 o Node N1 initiates a traceroute probe packet with a monotonically 552 increasing value of hop count and SRH as follows (2001:DB8:A:1::, 553 2001:DB8:B:2:C31::) (2001:DB8:B:4::, 2001:DB8:B:2:C31::; SL=1; 554 NH=UDP)(Traceroute probe). 556 o When node N2 receives the packet with hop-count = 1, it processes 557 the hop count expiry. Specifically, the node N2 responses with 558 the ICMPv6 message (Type: "Time Exceeded", Code: "Time to Live 559 exceeded in Transit"). 561 o When Node N2 receives the packet with hop-count > 1, it performs 562 the standard SRH processing. Specifically, it executes the END.X 563 behavior (2001:DB8:B:2:C31::) on the traceroute probe. If 564 2001:DB8:B:2:C31:: is a PSP SID, node N4 executes the SID like any 565 other data packet with DA = 2001:DB8:B:2:C31:: and removes the 566 SRH. 568 o When node N3, which is a classic IPv6 node, receives the packet 569 with hop-count = 1, it processes the hop count expiry. 570 Specifically, the node N3 responses with the ICMPv6 message (Type: 571 "Time Exceeded", Code: "Time to Live exceeded in Transit"). 573 o When node N3, which is a classic IPv6 node, receives the packet 574 with hop-count > 1, it performs the standard IPv6 processing. 575 Specifically, it forwards the traceroute probe based on DA 576 2001:DB8:B:4:: in the IPv6 header. 578 o When node N4 receives the packet with DA set to the local SID 579 2001:DB8:B:4::, it processes the END SID. 581 o If the target SID (2001:DB8:B:4::) is not locally instantiated, 582 the packet is discarded. 584 o If the target SID (2001:DB8:B:4::) is locally instantiated, the 585 node processes the upper layer header. As part of the upper layer 586 header processing node N4 responses with the ICMPv6 message (Type: 587 Destination unreachable, Code: Port Unreachable). 589 Figure 4 displays a sample traceroute output for this example. 591 > traceroute 2001:DB8:B:4:C52:: via segment-list 2001:DB8:B:2:C31:: 593 Tracing the route to SID 2001:DB8:B:4:C52:: 594 1 2001:DB8:1:2:21:: 0.512 msec 0.425 msec 0.374 msec 595 DA: 2001:DB8:B:2:C31::, 596 SRH:(2001:DB8:B:4:C52::, 2001:DB8:B:2:C31::; SL=1) 597 2 2001:DB8:2:3:31:: 0.721 msec 0.810 msec 0.795 msec 598 DA: 2001:DB8:B:4:C52::, 599 SRH:(2001:DB8:B:4:C52::, 2001:DB8:B:2:C31::; SL=0) 600 3 2001:DB8:3:4:41:: 0.921 msec 0.816 msec 0.759 msec 601 DA: 2001:DB8:B:4:C52::, 602 SRH:(2001:DB8:B:4:C52::, 2001:DB8:B:2:C31::; SL=0) 604 Figure 4 A sample output for hop-by-hop traceroute to a SID 606 3.3. A Hybrid OAM Using O-flag 608 This section illustrates a hybrid OAM mechanism using the the 609 SRH.Flags.O-flag. Without loss of the generality, the illustration 610 assumes N100 is a centralized controller. 612 The illustration is different than the In-situ OAM defined in [I.D- 613 draft-ietf-ippm-ioam-data]. This is because In-situ OAM records 614 operational and telemetry information in the packet as the packet 615 traverses a path between two points in the network [I.D-draft-ietf- 616 ippm-ioam-data]. The illustration in section 3 does not require the 617 recording of OAM data in the packet. 619 The illustration does not assume any formats for exporting the data 620 elements or the data elements that needs to be exported. 622 Consider the example where the user wants to monitor sampled IPv4 VPN 623 100 traffic going from CE1 to CE2 via a low latency SR policy P 624 installed at Node N1. To exercise a low latency path, the SR Policy 625 P forces the packet via segments 2001:DB8:B:2:C31:: and 626 2001:DB8:B:4:C52::. The VPN SID at N7 associated with VPN100 is 627 2001:DB8:B:7:DT100::. 2001:DB8:B:7:DT100:: is a USP SID. N1, N4, 628 and N7 are capable of processing SRH.Flags.O-flag but N2 is not 629 capable of processing SRH.Flags.O-flag. N100 is the centralized 630 controller capable of processing and correlating the copy of the 631 packets sent from nodes N1, N4, and N7. N100 is aware of 632 SRH.Flags.O-flag processing capabilities. Controller N100 with the 633 help from nodes N1, N4, N7 and implements a hybrid OAM mechanism 634 using the SRH.Flags.O-flag as follows: 636 o A packet P1:(IPv4 header)(payload) is sent from CE1 to Node N1. 638 o Node N1 steers the packet P1 through the Policy P. Based on a 639 local configuration, Node N1 also implements logic to sample 640 traffic steered through policy P for hybrid OAM purposes. 641 Specification for the sampling logic is beyond the scope of this 642 document. Consider the case where packet P1 is classified as a 643 packet to be monitored via the hybrid OAM. Node N1 sets 644 SRH.Flags.O-flag during encapsulation required by policy P. As 645 part of setting the SRH.Flags.O-flag, node N1 also send a 646 timestamped copy of the packet P1: (2001:DB8:A:1::, 647 2001:DB8:B:2:C31::) (2001:DB8:B:7:DT100::, 2001:DB8:B:4:C52::, 648 2001:DB8:B:2:C31::; SL=2; O-flag=1; NH=IPv4)(IPv4 header)(payload) 649 to a local OAM process. The local OAM process sends a full or 650 partial copy of the packet P1 to the controller N100. The OAM 651 process includes the recorded timestamp, additional OAM 652 information like incoming and outgoing interface, etc. along with 653 any applicable metadata. Node N1 forwards the original packet 654 towards the next segment 2001:DB8:B:2:C31::. 656 o When node N2 receives the packet with SRH.Flags.O-flag set, it 657 ignores the SRH.Flags.O-flag. This is because node N2 is not 658 capable of processing the O-flag. Node N2 performs the standard 659 SRv6 SID and SRH processing. Specifically, it executes the END.X 660 (refer [I-D.ietf-spring-srv6-network-programming]) behavior 661 (2001:DB8:B:2:C31::) and forwards the packet P1 (2001:DB8:A:1::, 662 2001:DB8:B:4:C52::) (2001:DB8:B:7:DT100::, 2001:DB8:B:4:C52::, 663 2001:DB8:B:2:C31::; SL=1; O-flag=1; NH=IPv4)(IPv4 header)(payload) 664 over link 3 towards Node N3. 666 o When node N3, which is a classic IPv6 node, receives the packet P1 667 , it performs the standard IPv6 processing. Specifically, it 668 forwards the packet P1 based on DA 2001:DB8:B:4:C52:: in the IPv6 669 header. 671 o When node N4 receives the packet P1 (2001:DB8:A:1::, 672 2001:DB8:B:4:C52::) (2001:DB8:B:7:DT100::, 2001:DB8:B:4:C52::, 673 2001:DB8:B:2:C31::; SL=1; O-flag=1; NH=IPv4)(IPv4 674 header)(payload), it processes the SRH.Flags.O-flag. As part of 675 processing the O-flag, it sends a timestamped copy of the packet 676 to a local OAM process. The local OAM process sends a full or 677 partial copy of the packet P1 to the controller N100. The OAM 678 process includes the recorded timestamp, additional OAM 679 information like incoming and outgoing interface, etc. along with 680 any applicable metadata. Node N4 performs the standard SRv6 SID 681 and SRH processing on the original packet P1. Specifically, it 682 executes the END.X behavior (2001:DB8:B:4:C52::) and forwards the 683 packet P1 (2001:DB8:A:1::, 2001:DB8:B:7:DT100::) 684 (2001:DB8:B:7:DT100::, 2001:DB8:B:4:C52::, 2001:DB8:B:2:C31::; 685 SL=0; O-flag=1; NH=IPv4)(IPv4 header)(payload) over link 10 686 towards Node N5. 688 o When node N5, which is a classic IPv6 node, receives the packet 689 P1, it performs the standard IPv6 processing. Specifically, it 690 forwards the packet based on DA 2001:DB8:B:7:DT100:: in the IPv6 691 header. 693 o When node N7 receives the packet P1 (2001:DB8:A:1::, 694 2001:DB8:B:7:DT100::) (2001:DB8:B:7:DT100::, 2001:DB8:B:4:C52::, 695 2001:DB8:B:2:C31::; SL=0; O-flag=1; NH=IPv4)(IPv4 696 header)(payload), it processes the SRH.Flags.O-flag. As part of 697 processing the O-flag, it sends a timestamped copy of the packet 698 to a local OAM process. The local OAM process sends a full or 699 partial copy of the packet P1 to the controller N100. The OAM 700 process includes the recorded timestamp, additional OAM 701 information like incoming and outgoing interface, etc. along with 702 any applicable metadata. Node N4 performs the standard SRv6 SID 703 and SRH processing on the original packet P1. Specifically, it 704 executes the VPN SID (2001:DB8:B:7:DT100::) and based on lookup in 705 table 100 forwards the packet P1 (IPv4 header)(payload) towards CE 706 2. 708 o The controller N100 processes and correlates the copy of the 709 packets sent from nodes N1, N4 and N7 to find segment-by-segment 710 delays and provide other hybrid OAM information related to packet 711 P1. 713 o The process continues for any other sampled packets. 715 3.4. Monitoring of SRv6 Paths 717 In the recent past, network operators demonstrated interest in 718 performing network OAM functions in a centralized manner. [RFC8403] 719 describes such a centralized OAM mechanism. Specifically, the 720 document describes a procedure that can be used to perform path 721 continuity check between any nodes within an SR domain from a 722 centralized monitoring system. However, the document focuses on SR 723 networks with MPLS data plane. This document describes how the 724 concept can be used to perform path monitoring in an SRv6 network 725 from a centralized controller. 727 In the reference topology in Figure 1, N100 uses an IGP protocol like 728 OSPF or ISIS to get the topology view within the IGP domain. N100 729 can also use BGP-LS to get the complete view of an inter-domain 730 topology. The controller leverages the visibility of the topology to 731 monitor the paths between the various endpoints. 733 The controller N100 advertises an END (refer [I-D.ietf-spring-srv6- 734 network-programming]) SID 2001:DB8:B:100:1::. To monitor any 735 arbitrary SRv6 paths, the controller can create a loopback probe that 736 originates and terminates on Node N100. To distinguish between a 737 failure in the monitored path and loss of connectivity between the 738 controller and the network, Node N100 runs a suitable mechanism to 739 monitor its connectivity to the monitored network. 741 The loopback probes are exemplified using an example where controller 742 N100 needs to verify a segment list <2001:DB8:B:2:C31::, 743 2001:DB8:B:4:C52::>: 745 o N100 generates an OAM packet (2001:DB8:A:100::, 746 2001:DB8:B:2:C31::)(2001:DB8:B:100:1::, 2001:DB8:B:4:C52::, 747 2001:DB8:B:2:C31::, SL=2)(OAM Payload). The controller routes the 748 probe packet towards the first segment, which is 749 2001:DB8:B:2:C31::. 751 o Node N2 executes the END.X behavior (2001:DB8:B:2:C31::) and 752 forwards the packet (2001:DB8:A:100::, 753 2001:DB8:B:4:C52::)(2001:DB8:B:100:1::, 2001:DB8:B:4:C52::, 754 2001:DB8:B:2:C31::, SL=1)(OAM Payload) on link3 to N3. 756 o Node N3, which is a classic IPv6 node, performs the standard IPv6 757 processing. Specifically, it forwards the packet based on the DA 758 2001:DB8:B:4:C52:: in the IPv6 header. 760 o Node N4 executes the END.X behavior (2001:DB8:B:4:C52::) and 761 forwards the packet (2001:DB8:A:100::, 762 2001:DB8:B:100:1::)(2001:DB8:B:100:1::, 2001:DB8:B:4:C52::, 763 2001:DB8:B:2:C31::, SL=0)(OAM Payload) on link10 to N5. 765 o Node N5, which is a classic IPv6 node, performs the standard IPv6 766 processing. Specifically, it forwards the packet based on the DA 767 2001:DB8:B:100:1:: in the IPv6 header. 769 o Node N100 executes the standard SRv6 END behavior. It 770 decapsulates the header and consume the probe for OAM processing. 771 The information in the OAM payload is used to detect any missing 772 probes, round trip delay, etc. 774 The OAM payload type or the information carried in the OAM probe is a 775 local implementation decision at the controller and is outside the 776 scope of this document. 778 4. Implementation Status 780 This section is to be removed prior to publishing as an RFC. 782 See [I-D.matsushima-spring-srv6-deployment-status] for updated 783 deployment and interoperability reports. 785 5. Security Considerations 787 This document does not define any new protocol extensions and relies 788 on existing procedures defined for ICMP. This document does not 789 impose any additional security challenges to be considered beyond 790 security considerations described in [RFC4884], [RFC4443], [RFC0792], 791 and [RFC8754]. 793 6. IANA Considerations 795 6.1. Segment Routing Header Flags 797 This I-D requests to IANA to allocate bit position 2, within the 798 "Segment Routing Header Flags" registry defined in [RFC8754]. 800 7. Acknowledgements 802 The authors would like to thank Joel M. Halpern, Greg Mirsky, Bob 803 Hinden, Loa Andersson, Gaurav Naik, Ketan Talaulikar and Haoyu Song 804 for their review comments. 806 8. Contributors 808 The following people have contributed to this document: 810 Robert Raszuk 811 Bloomberg LP 812 Email: robert@raszuk.net 814 John Leddy 815 Individual 816 Email: john@leddy.net 818 Gaurav Dawra 819 LinkedIn 820 Email: gdawra.ietf@gmail.com 822 Bart Peirens 823 Proximus 824 Email: bart.peirens@proximus.com 826 Nagendra Kumar 827 Cisco Systems, Inc. 828 Email: naikumar@cisco.com 830 Carlos Pignataro 831 Cisco Systems, Inc. 832 Email: cpignata@cisco.com 834 Rakesh Gandhi 835 Cisco Systems, Inc. 836 Canada 837 Email: rgandhi@cisco.com 838 Frank Brockners 839 Cisco Systems, Inc. 840 Germany 841 Email: fbrockne@cisco.com 843 Darren Dukes 844 Cisco Systems, Inc. 845 Email: ddukes@cisco.com 847 Cheng Li 848 Huawei 849 Email: chengli13@huawei.com 851 Faisal Iqbal 852 Individual 853 Email: faisal.ietf@gmail.com 855 9. References 857 9.1. Normative References 859 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 860 Requirement Levels", BCP 14, RFC 2119, 861 DOI 10.17487/RFC2119, March 1997, 862 . 864 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 865 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 866 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 867 . 869 9.2. Informative References 871 [I-D.ietf-spring-srv6-network-programming] 872 Filsfils, C., Camarillo, P., Leddy, J., Voyer, D., 873 Matsushima, S., and Z. Li, "SRv6 Network Programming", 874 draft-ietf-spring-srv6-network-programming-16 (work in 875 progress), June 2020. 877 [I-D.matsushima-spring-srv6-deployment-status] 878 Matsushima, S., Filsfils, C., Ali, Z., Li, Z., and K. 879 Rajaraman, "SRv6 Implementation and Deployment Status", 880 draft-matsushima-spring-srv6-deployment-status-07 (work in 881 progress), April 2020. 883 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 884 RFC 792, DOI 10.17487/RFC0792, September 1981, 885 . 887 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 888 Control Message Protocol (ICMPv6) for the Internet 889 Protocol Version 6 (IPv6) Specification", STD 89, 890 RFC 4443, DOI 10.17487/RFC4443, March 2006, 891 . 893 [RFC4884] Bonica, R., Gan, D., Tappan, D., and C. Pignataro, 894 "Extended ICMP to Support Multi-Part Messages", RFC 4884, 895 DOI 10.17487/RFC4884, April 2007, 896 . 898 [RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J. 899 Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)", 900 RFC 5357, DOI 10.17487/RFC5357, October 2008, 901 . 903 [RFC5476] Claise, B., Ed., Johnson, A., and J. Quittek, "Packet 904 Sampling (PSAMP) Protocol Specifications", RFC 5476, 905 DOI 10.17487/RFC5476, March 2009, 906 . 908 [RFC5837] Atlas, A., Ed., Bonica, R., Ed., Pignataro, C., Ed., Shen, 909 N., and JR. Rivers, "Extending ICMP for Interface and 910 Next-Hop Identification", RFC 5837, DOI 10.17487/RFC5837, 911 April 2010, . 913 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 914 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 915 . 917 [RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken, 918 "Specification of the IP Flow Information Export (IPFIX) 919 Protocol for the Exchange of Flow Information", STD 77, 920 RFC 7011, DOI 10.17487/RFC7011, September 2013, 921 . 923 [RFC7012] Claise, B., Ed. and B. Trammell, Ed., "Information Model 924 for IP Flow Information Export (IPFIX)", RFC 7012, 925 DOI 10.17487/RFC7012, September 2013, 926 . 928 [RFC7799] Morton, A., "Active and Passive Metrics and Methods (with 929 Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799, 930 May 2016, . 932 [RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S. 933 Pallagatti, "Seamless Bidirectional Forwarding Detection 934 (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016, 935 . 937 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 938 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 939 May 2017, . 941 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 942 Decraene, B., Litkowski, S., and R. Shakir, "Segment 943 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 944 July 2018, . 946 [RFC8403] Geib, R., Ed., Filsfils, C., Pignataro, C., Ed., and N. 947 Kumar, "A Scalable and Topology-Aware MPLS Data-Plane 948 Monitoring System", RFC 8403, DOI 10.17487/RFC8403, July 949 2018, . 951 [RFC8762] Mirsky, G., Jun, G., Nydell, H., and R. Foote, "Simple 952 Two-Way Active Measurement Protocol", RFC 8762, 953 DOI 10.17487/RFC8762, March 2020, 954 . 956 Authors' Addresses 958 Zafar Ali 959 Cisco Systems 961 Email: zali@cisco.com 963 Clarence Filsfils 964 Cisco Systems 966 Email: cfilsfil@cisco.com 968 Satoru Matsushima 969 Softbank 971 Email: satoru.matsushima@g.softbank.co.jp 973 Daniel Voyer 974 Bell Canada 976 Email: daniel.voyer@bell.ca 977 Mach Chen 978 Huawei 980 Email: mach.chen@huawei.com