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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) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 SPRING Working Group Z. Ali 3 Internet-Draft C. Filsfils 4 Intended status: Standards Track N. Kumar 5 Expires: August 30, 2018 C. Pignataro 6 F. Iqbal 7 R. Gandhi 8 Cisco Systems, Inc. 9 J. Leddy 10 Comcast 11 S. Matsushima 12 SoftBank 13 R. Raszuk 14 Bloomberg LP 15 B. Peirens 16 Proximus 17 G. Naik 18 Drexel University 19 February 26, 2018 21 Operations, Administration, and Maintenance (OAM) in Segment 22 Routing Networks with IPv6 Data plane (SRv6) 23 draft-ali-spring-srv6-oam-00.txt 25 Abstract 27 This document describes mechanisms for Operations, Administration, 28 and Maintenance (OAM) in Segment Routing with IPv6 data plane (SRv6) 29 network. 31 Status of This Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at http://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 Copyright Notice 48 Copyright (c) 2018 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2. Conventions Used in This Document . . . . . . . . . . . . . . 3 65 2.1. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 3 66 2.2. Terminology and Reference Topology . . . . . . . . . . . . 3 67 3. OAM Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . 4 68 3.1. Ping . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 69 3.1.1. Classic Ping . . . . . . . . . . . . . . . . . . . . . 5 70 3.1.2. Pinging SID Function . . . . . . . . . . . . . . . . . 6 71 3.1.2.1. End-to-end Ping Using END.OTP . . . . . . . . . . 7 72 3.1.2.2. Segment-by-segment Ping Using O-bit (Proof of 73 Transit) . . . . . . . . . . . . . . . . . . . . . 8 74 3.2. Error Reporting . . . . . . . . . . . . . . . . . . . . . 9 75 3.3. Traceroute . . . . . . . . . . . . . . . . . . . . . . . . 10 76 3.3.1. Classic Traceroute . . . . . . . . . . . . . . . . . . 10 77 3.3.2. Traceroute to a SID Function . . . . . . . . . . . . . 11 78 3.3.2.1. Hop-by-hop Traceroute Using END.OTP . . . . . . . 12 79 3.3.2.2. Tracing SRv6 Overlay . . . . . . . . . . . . . . . 14 80 4. In-situ OAM Applicability . . . . . . . . . . . . . . . . . . 15 81 5. Seamless BFD Applicability . . . . . . . . . . . . . . . . . . 16 82 6. Monitoring of SRv6 Paths . . . . . . . . . . . . . . . . . . . 16 83 7. Security Considerations . . . . . . . . . . . . . . . . . . . 17 84 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 85 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 86 9.1. Normative References . . . . . . . . . . . . . . . . . . . 17 87 9.2. Informative References . . . . . . . . . . . . . . . . . . 18 88 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20 89 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 91 1. Introduction 93 This document describes mechanisms for Operations, Administrations, 94 and Maintenance (OAM) in Segment Routing using IPv6 data plane (SRv6) 95 networks. 97 Additional mechanisms will be added in a future revision of the 98 document. 100 2. Conventions Used in This Document 102 2.1. Abbreviations 104 ECMP: Equal Cost Multi-Path. 106 SID: Segment ID. 108 SL: Segment Left. 110 SR: Segment Routing. 112 SRH: Segment Routing Header. 114 SRv6: Segment Routing with IPv6 Data plane. 116 TC: Traffic Class. 118 UCMP: Unequal Cost Multi-Path. 120 2.2. Terminology and Reference Topology 122 In this document, the simple topology shown in Figure 1 is used for 123 illustration. 125 -------- 126 +------------------------| N100 |------------------------+ 127 | -------- | 128 | | 129 ====== link1====== link3------ link5====== link9------ 130 ||N1||======||N2||======| N3 |======||N4||======| N5 | 131 || ||------|| ||------| |------|| ||------| | 132 ====== link2====== link4------ link6======link10------ 133 | | 134 | ------ | 135 +--------| N6 |--------+ 136 link7 | | link8 137 ------ 139 Figure 1: Reference Topology 141 In the reference topology: 143 Nodes N1, N2, and N4 are SRv6 capable nodes. 145 Nodes N3, N5 and N6 are classic IPv6 nodes. 147 Node 100 is a controller. 149 Node Nk has a classic IPv6 loopback address Bk::/128 151 Node Nk has Ak::/48 for its local SID space from which Local SIDs are 152 explicitly allocated. 154 The IPv6 address of the nth Link between node X and Y at the X side 155 is represented as 2001:DB8:X:Y:Xn::, e.g., the IPv6 address of link6 156 (the 2nd link) between N3 and N4 at N3 in Figure 1 is 157 2001:DB8:3:4:32::. Similarly, the IPv6 address of link5 (the 1st 158 link between N3 and N4) at node 3 is 2001:DB8:3:4:31::. 160 Ak::0 is explicitly allocated as the END function at Node k. 162 Ak::Cij is explicitly allocated as the END.X function at node k 163 towards neighbor node i via jth Link between node i and node j. e.g., 164 A2::C31 represents END.X at N2 towards N3 via link3 (the 1st link 165 between N2 and N3). Similarly, A4::C52 represents the END.X at N4 166 towards N5 via link10. 168 represents a SID list where S1 is the first SID and S3 169 is the last SID. (S3, S2, S1; SL) represents the same SID list but 170 encoded in the SRH format where the rightmost SID (S1) in the SRH is 171 the first SID and the leftmost SID (S3) in the SRH is the last SID. 173 (SA, DA) (S3, S2, S1; SL) represents an IPv6 packet, SA is the IPv6 174 Source Address, DA the IPv6 Destination Address, (S3, S2, S1; SL) is 175 the SRH header that includes the SID list . 177 SR policy is defined in Section 3 of 178 [I-D.spring-segment-routing-policy]. 180 3. OAM Mechanisms 182 This section describes how ping and traceroute mechanisms can be used 183 in an SRv6 network. Additional OAM mechanisms will be added in a 184 future revision of the document. 186 3.1. Ping 188 [RFC4443] describes Internet Control Message Protocol for IPv6 189 (ICMPv6) that is used by IPv6 devices for network diagnostic and 190 error reporting purposes. As Segment Routing with IPv6 data plane 191 (SRv6) simply adds a new type of Routing Extension Header, existing 192 ICMPv6 mechanisms can be used in an SRv6 network. This section 193 describes the applicability of ICMPv6 in the SRv6 network and how the 194 existing ICMPv6 mechanisms can be used for providing OAM 195 functionality. 197 Throughout this document, unless otherwise specified, the acronym 198 ICMPv6 refers to multi-part ICMPv6 messages [RFC4884]. The document 199 does not propose any changes to the standard ICMPv6 [RFC4443], 200 [RFC4884] or standard ICMPv4 [RFC792]. 202 There is no hardware or software change required for ping operation 203 at the classic IPv6 nodes in an SRv6 network. This includes the 204 classic IPv6 node with ingress, egress or transit roles. 205 Furthermore, no protocol changes are required to the standard ICMPv6 206 [RFC4443], [RFC4884] or standard ICMPv4 [RFC792]. In other words, 207 existing ICMP ping mechanisms work seamlessly in SRv6 networks. 209 The following subsections outline some use cases of the ICMP ping in 210 SRv6 networks. 212 3.1.1. Classic Ping 214 The existing mechanism to ping a remote IP prefix, along the shortest 215 path, continues to work without any modification. The initiator may 216 be an SRv6 node or a classic IPv6 node. Similarly, the egress or 217 transit may be an SRv6 capable node or a classic IPv6 node. 219 If an SRv6 capable ingress node wants to ping an IPv6 prefix via an 220 arbitrary segment list , it needs to initiate ICMPv6 ping 221 with an SR header containing the SID list . This is 222 illustrated using the topology in Figure 1. Assume all the links 223 have IGP metric 10 except both links between node N2 and node N3, 224 which have IGP metric set to 100. User issues a ping from node N1 to 225 a loopback of node N5, via via segment list . 227 Figure 2 contains sample output for a ping request initiated at node 228 N1 to the loopback address of node N5 via a segment list . 231 > ping B5:: via segment-list A2::C31, A4::C52 233 Sending 5, 100-byte ICMP Echos to B5::, timeout is 2 seconds: 235 !!!!! 236 Success rate is 100 percent (5/5), round-trip min/avg/max = 0.625 237 /0.749/0.931 ms 239 Figure 2: A sample ping output at an SRv6 capable node 241 All transit nodes process the echo request message like any other 242 data packet carrying SR header and hence do not require any change. 243 Similarly, the egress node (IPv6 classic or SRv6 capable) does not 244 require any change to process the ICMPv6 echo request. For example, 245 in the ping example of Figure 2: 247 o Node N1 initiates an ICMPv6 ping packet with SRH as follows 248 (B1::,A2::C31)(B1::, A4::C52, A2::C31, SL=2, NH: ICMPv6)(ICMPv6 249 Echo Request). 251 o Node N2, which is an SRv6 capable node, performs the standard SRH 252 processing. Specifically, it executes the END.X function 253 (A2::C31) on the echo request packet. 255 o Node N3, which is a classic IPv6 node, performs the standard IPv6 256 processing. Specifically, it forwards the echo request based on 257 DA A4::C52 in the IPv6 header. 259 o Node N4, which is an SRv6 capable node, performs the standard SRH 260 processing. Specifically, it observes the END.X function 261 (A4::C52) with PSP (Penultimate Segment Popping) on the echo 262 request packet and removes the SRH and forwards the packet across 263 link10 to N5. 265 o The echo request packet at N5 arrives as an IPv6 packet without a 266 SRH. Node N5, which is a classic IPv6 node, performs the standard 267 IPv6/ICMPv6 processing on the echo request and responds, 268 accordingly. 270 3.1.2. Pinging SID Function 272 The classic ping described in the previous section cannot be used to 273 ping a remote SID function, as explained using an example in the 274 following. 276 Consider the case where the user wants to ping the remote SID 277 function A4::C52, via A2::C31, from node N1. Node N1 constructs the 278 ping packet (B1::0, A2::C31)( A4::C52, A2::C31, 279 SL=1;NH=ICMPv6)(ICMPv6 Echo Request). When the node N4 receives the 280 ICMPv6 echo request with DA set to A4::C52 and next header set to 281 ICMPv6, it silently drops it (as per 282 [I-D.filsfils-spring-srv6-network-programming]). To solve this 283 problem, the initiator needs to mark the ICMPv6 echo request as an 284 OAM packet. 286 The OAM packets are identified either by setting the O-bit in SRH 287 [I-D.6man-segment-routing-header] or by inserting the SID Function 288 END.OTP at an appropriate place in the SRH 289 [I-D.filsfils-spring-srv6-network-programming]. 291 In an SRv6 network, the user can exercise two flavors of the ping: 292 end-to-end ping or segment-by-segment ping, as outlined in the 293 following. 295 3.1.2.1. End-to-end Ping Using END.OTP 297 Consider the same example where the user wants to ping a remote SID 298 function A4::C52 , via A2::C31, from node N1. To force a punt of the 299 ICMPv6 echo request at the node N4, node N1 inserts the SID function 300 END.OTP just before the target SID A4::C52 in the SRH. The ICMPv6 301 echo request is processed at the individual nodes along the path as 302 follows: 304 o Node N1 initiates an ICMPv6 ping packet with SRH as follows 305 (B1::0, A2::C31)(A4::C52, A4::OTP, A2::C31; SL=2; 306 NH=ICMPv6)(ICMPv6 Echo Request). 308 o Node N2, which is an SRv6 capable node, performs the standard SRH 309 processing. Specifically, it executes the END.X function 310 (A2::C31) on the echo request packet. 312 o Node N3 receives the packet as follows (B1::0, A4::OTP)(A4::C52, 313 A4::OTP, A2::C31 ; SL=1; NH=ICMPv6)(ICMPv6 Echo Request). Node 314 N3, which is a classic IPv6 node, performs the standard IPv6 315 processing. Specifically, it forwards the echo request based on 316 DA A4::OTP in the IPv6 header. 318 o When node N4 receives the packet (B1::0, A4::OTP)(A4::C52,A4::OTP, 319 A2::C31 ; SL=1; NH=ICMPv6)(ICMPv6 Echo Request), it processes the 320 SID Function END.OTP, as described in the pseudocode in 321 [I-D.filsfils-spring-srv6-network-programming]. The packet gets 322 punted to the ICMPv6 process for processing. The ICMPv6 process 323 checks if the next SID in SRH (the target SID A4::C52) is locally 324 programmed. 326 o If the target SID is not locally programmed, N4 responses with the 327 ICMPv6 message (Type: "SRv6 OAM (TBA1 by IANA)", Code: "SID not 328 locally implemented (TBA2 by IANA)"); otherwise a success is 329 returned. 331 3.1.2.2. Segment-by-segment Ping Using O-bit (Proof of Transit) 333 Consider the same example where the user wants to ping a remote SID 334 function A4::C52 , via A2::C31, from node N1. However, in this ping, 335 the node N1 wants to get a response from each segment node in the 336 SRH. In other words, in the segment-by-segment ping case, the node 337 N1 expects a response from node N2 and node N4 for their respective 338 local SID function. 340 To force a punt of the ICMPv6 echo request at node N2 and node N4, 341 node N1 sets the O-bit in SRH [I-D.6man-segment-routing-header]. The 342 ICMPv6 echo request is processed at the individual nodes along the 343 path as follows: 345 o Node N1 initiates an ICMPv6 ping packet with SRH as follows 346 (B1::0, A2::C31)(A4::C52, A2::C31; SL=1, Flags.O=1; 347 NH=ICMPv6)(ICMPv6 Echo Request). 349 o When node N2 receives the packet (B1::0, A2::C31)(A4::C52, 350 A2::C31; SL=1, Flags.O=1; NH=ICMPv6)(ICMPv6 Echo Request) packet, 351 it processes the O-bit in SRH, as described in the pseudo code in 352 [I-D.filsfils-spring-srv6-network-programming]. A time-stamped 353 copy of the packet is punted to the ICMPv6 process in control 354 plane for processing. Node N2 continues to apply the A2::C31 SID 355 function on the original packet and forwards it, accordingly. Due 356 to SRH.Flags.O=1, Node N2 also disables the PSP behaviour, i.e., 357 does not remove the SRH. The ICMPv6 process at node N2 checks if 358 its local SID (A2::C31) is locally programmed or not and responds 359 to the ICMPv6 Echo Request. 361 o If the target SID is not locally programmed, N4 responses with the 362 ICMPv6 message (Type: "SRv6 OAM (TBA1 by IANA)", Code: "SID not 363 locally implemented (TBA2 by IANA)"); otherwise a success is 364 returned. Note that, as mentioned in 365 [I-D.filsfils-spring-srv6-network-programming], if node N2 does 366 not support the O-bit, it simply ignores it and process the local 367 SID, A2::C31. 369 o Node N3, which is a classic IPv6 node, performs standard IPv6 370 processing. Specifically, it forwards the echo request based on 371 DA A4::C52 in the IPv6 header. 373 o When node N4 receives the packet (B1::0, A4::C52)(A4::C52, 374 A2::C31; SL=0, Flags.O=1; NH=ICMPv6)(ICMPv6 Echo Request), it 375 processes the O-bit in SRH, as described in the pseudo code in 376 [I-D.filsfils-spring-srv6-network-programming]. A time-stamped 377 copy of the packet is punted to the ICMPv6 process in control 378 plane for processing. The ICMPv6 process at node N4 checks if its 379 local SID (A2::C31) is locally programmed or not and responds to 380 the ICMPv6 Echo Request. 382 If the target SID is not locally programmed, N4 responses with the 383 ICMPv6 message (Type: "SRv6 OAM (TBA1 by IANA)", Code: "SID not 384 locally implemented (TBA2 by IANA)"); otherwise a success is 385 returned. 387 Support for O-bit is part of node capability advertisement. This 388 enables node N1 to know which segment nodes are capable of responding 389 to the ICMPv6 echo request. Node N1 processes the echo responses and 390 presents the data to the user, accordingly. 392 Please note that segment-by-segment ping described in this Section 393 can be used to address proof of transit use-case. 395 3.2. Error Reporting 397 Any IPv6 node can use ICMPv6 control messages to report packet 398 processing errors to the source that originated the datagram packet. 399 To name a few such scenarios: 401 - If the router receives an undeliverable IP datagram, or 403 - If the router receives a packet with a Hop Limit of zero, or 405 - If the router receives a packet such that if the router decrements 406 the packet's Hop Limit it becomes zero, or 408 - If the router receives a packet with problem with a field in the 409 IPv6 header or the extension headers such that it cannot complete 410 processing the packet, or 412 - If the router cannot forward a packet because the packet is larger 413 than the MTU of the outgoing link. 415 In the scenarios listed above, the ICMPv6 response also contains the 416 IP header, IP extension headers and leading payload octets of the 417 "original datagram" to which the ICMPv6 message is a response. 418 Specifically, the "Destination Unreachable Message", "Time Exceeded 419 Message", "Packet Too Big Message" and "Parameter Problem Message" 420 ICMPV6 messages can contain as much of the invoking packet as 421 possible without the ICMPv6 packet exceeding the minimum IPv6 MTU 422 [RFC4443], [RFC4884]. In an SRv6 network, the copy of the invoking 423 packet contains the SR header. The packet originator can use this 424 information for diagnostic purposes. For example, traceroute can use 425 this information as detailed in the following. 427 3.3. Traceroute 429 There is no hardware or software change required for traceroute 430 operation at the classic IPv6 nodes in an SRv6 network. That 431 includes the classic IPv6 node with ingress, egress or transit roles. 432 Furthermore, no protocol changes are required to the standard 433 traceroute operations. In other words, existing traceroute 434 mechanisms work seamlessly in the SRv6 networks. 436 The following subsections outline some use cases of the traceroute in 437 the SRv6 networks. 439 3.3.1. Classic Traceroute 441 The existing mechanism to traceroute a remote IP prefix, along the 442 shortest path, continues to work without any modification. The 443 initiator may be an SRv6 node or a classic IPv6 node. Similarly, the 444 egress or transit node may be an SRv6 node or a classic IPv6 node. 446 If an SRv6 capable ingress node wants to traceroute to IPv6 prefix 447 via an arbitrary segment list , it needs to initiate 448 traceroute probe with an SR header containing the SID list . This is illustrated using the topology in Figure 1. Assume all 450 the links have IGP metric 10 except both links between node N2 and 451 node N3, which have IGP metric set to 100. User issues a traceroute 452 from node N1 to a loopback of node N5, via segment list . Figure 3 contains sample output for the traceroute 454 request. 456 > traceroute B5:: via segment-list A2::C31, A4::C52 458 Tracing the route to B5:: 460 1 2001:DB8:1:2:21:: 0.512 msec 0.425 msec 0.374 msec 461 SRH: (B5::, A4::C52, A2::C31, SL=2) 463 2 2001:DB8:2:3:31:: 0.721 msec 0.810 msec 0.795 msec 464 SRH: (B5::, A4::C52, A2::C31, SL=1) 466 3 2001:DB8:3:4:41:: 0.921 msec 0.816 msec 0.759 msec 467 SRH: (B5::, A4::C52, A2::C31, SL=1) 469 4 2001:DB8:4:5:52:: 0.879 msec 0.916 msec 1.024 msec 471 Figure 3: A sample traceroute output at an SRv6 capable node 473 Please note that information for hop2 is returned by N3, which is a 474 classic IPv6 node. Nonetheless, the ingress node is able to display 475 SR header contents as the packet travels through the IPv6 classic 476 node. This is because the "Time Exceeded Message" ICMPv6 message can 477 contain as much of the invoking packet as possible without the ICMPv6 478 packet exceeding the minimum IPv6 MTU [RFC4443]. The SR header is 479 also included in these ICMPv6 messages initiated by the classic IPv6 480 transit nodes that are not running SRv6 software. Specifically, a 481 node generating ICMPv6 message containing a copy of the invoking 482 packet does not need to understand the extension header(s) in the 483 invoking packet. 485 The segment list information returned for hop1 is returned by N2, 486 which is an SRv6 capable node. Just like for hop2, the ingress node 487 is able to display SR header contents for hop1. 489 There is no difference in processing of the traceroute probe at an 490 IPv6 classic node and an SRv6 capable node. Similarly, both IPv6 491 classic and SRv6 capable nodes use the address of the interface on 492 which probe was received as the source address in the ICMPv6 493 response. ICMP extensions defined in [RFC5837] can be used to also 494 display information about the IP interface through which the datagram 495 would have been forwarded had it been forwardable, and the IP next 496 hop to which the datagram would have been forwarded, the IP interface 497 upon which a datagram arrived, the sub-IP component of an IP 498 interface upon which a datagram arrived. 500 The information about the IP address of the incoming interface on 501 which the traceroute probe was received by the reporting node is very 502 useful. This information can also be used to verify if SID functions 503 A2::C31 and A4::C52 are executed correctly by N2 and N4, 504 respectively. Specifically, the information displayed for hop2 505 contains the incoming interface address 2001:DB8:2:3::31 at N3. This 506 matches with the expected interface bound to END.X function A2::C31 507 (link3). Similarly, the information displayed for hop5 contains the 508 incoming interface address 2001:DB8:4:5::52 at N5. This matches with 509 the expected interface bound to the END.X function A4::C52 (link10). 511 3.3.2. Traceroute to a SID Function 513 The classic traceroute described in the previous Section cannot be 514 used to traceroute a remote SID function, as explained using an 515 example as follows. 517 Consider the case where the user wants to traceroute the remote SID 518 function A4::C52, via A2::C31, from node N1. Node N1 constructs the 519 traceroute packet (B1::0, A2::C31, HC=1) (A4::C52, A2::C31, SL=1; 520 NH=UDP) (traceroute probe). Even though Hop Count of the packet is 521 set to 1, when the node N4 receives the traceroute probe with DA set 522 to A4::C52 and next header set to UDP, it silently drops it (as per 524 [I-D.filsfils-spring-srv6-network-programming]). To solve this 525 problem, the initiator node needs to mark the traceroute probe as an 526 OAM packet. 528 The OAM packets are identified either by setting the O-bit in SRH 529 [I-D.6man-segment-routing-header] or by inserting the SID Function 530 END.OTP at an appropriate place in the SRH 531 [I-D.filsfils-spring-srv6-network-programming]. 533 In SRv6 networks, the user can exercise two flavors of the 534 traceroute: hop-by-hop traceroute or overlay traceroute. 536 o In hop-by-hop traceroute, user gets responses from all nodes 537 including classic IPv6 transit nodes, SRv6 capable transit nodes 538 as well as SRv6 capable segment endpoints. E.g., consider the 539 example where the user wants to traceroute to a remote SID 540 function A4::C52, via A2::C31, from node N1. The traceroute 541 output will also display information about node N3, which is a 542 transit (underlay) node. 544 o The overlay traceroute, on the other hand, does not trace the 545 underlay nodes. In other words, the overlay traceroute only 546 displays the nodes that acts as SRv6 segments along the route. 547 I.e., in the example where the user wants to traceroute to a 548 remote SID function A4::C52, via A2::C31, from node N1, the 549 overlay traceroute would only display the traceroute information 550 from node N2 and node N4 and will not display information from 551 node N3. 553 3.3.2.1. Hop-by-hop Traceroute Using END.OTP 555 In this Section, hop-by-hop traceroute to a SID function is 556 exemplified using UDP probes. However, the procedure is equally 557 applicable to other implementation of traceroute mechanism. 559 Consider the same example where the user wants to traceroute to a 560 remote SID function A4::C52 , via A2::C31, from node N1. To force a 561 punt of the traceroute probe only at the node N4, node N1 inserts the 562 SID Function END.OTP just before the target SID A4::C52 in the SRH. 563 The traceroute probe is processed at the individual nodes along the 564 path as follows: 566 o Node N1 initiates a traceroute probe packet with a monotonically 567 increasing value of hop count and SRH as follows 568 (B1::0,A2::C31)(A4::C52, A4::OTP, A2::C31; SL=2; 569 NH=UDP)(Traceroute probe). 571 o When node N2 receives the packet with hop-count = 1, it processes 572 the hop count expiry. Specifically, the node N2 responses with 573 the ICMPv6 message (Type: "Time Exceeded", Code: "Time to Live 574 exceeded in Transit"). 576 o When Node N2 receives the packet with hop-count > 1, it performs 577 the standard SRH processing. Specifically, it executes the END.X 578 function (A2::C31) on the traceroute probe. 580 o When node N3, which is a classic IPv6 node, receives the packet 581 (B1::0, A4::OTP)(A4::C52, A4::OTP, A2::C31 ; HC=1, SL=1; 582 NH=UDP)(Traceroute probe) with hop-count = 1, it processes the hop 583 count expiry. Specifically, the node N3 responses with the ICMPv6 584 message (Type: "Time Exceeded", Code: "Time to Live exceeded in 585 Transit"). 587 o When node N3, which is a classic IPv6 node, receives the packet 588 with hop-count > 1, it performs the standard IPv6 processing. 589 Specifically, it forwards the traceroute probe based on DA A4::OTP 590 in the IPv6 header. 592 o When node N4 receives the packet (B1::0, A4::OTP)(A4::C52, 593 A4::OTP, A2::C31 ; SL=1; HC=1, NH=UDP)(Traceroute probe), it 594 processes the SID Function END.OTP, as described in the pseudocode 595 in [I-D.filsfils-spring-srv6-network-programming]. The packet 596 gets punted to the traceroute process for processing. The 597 traceroute process checks if the next SID in SRH (the target SID 598 A4::C52) is locally programmed. If the target SID A4::C52 is 599 locally programmed, node N4 responses with the ICMPv6 message 600 (Type: Destination unreachable, Code: Port Unreachable). If the 601 target SID A4::C52 is not a local SID, node N4 silently drops the 602 traceroute probe. 604 Figure 4 displays a sample traceroute output for this example. 606 > traceroute srv6 A4::C52 via segment-list A2::C31 608 Tracing the route to SID function A4::C52 610 1 2001:DB8:1:2::21 0.512 msec 0.425 msec 0.374 msec SRH: 611 (A4::C52, A4::OTP, A2::C31; SL=2) 613 2 2001:DB8:2:3::31 0.721 msec 0.810 msec 0.795 msec SRH: 614 (A4::C52, A4::OTP, A2::C31; SL=1) 616 3 2001:DB8:3:4::41 0.921 msec 0.816 msec 0.759 msec SRH: 617 (A4::C52, A4::OTP, A2::C31; SL=1) 619 Figure 4: A sample output for hop-by-hop traceroute to a SID function 621 3.3.2.2. Tracing SRv6 Overlay 623 The overlay traceroute does not trace the underlay nodes, i.e., only 624 displays the nodes that acts as SRv6 segments along the path. This 625 is achieved by setting the SRH.Flags.O bit. 627 In this section, overlay traceroute to a SID function is exemplified 628 using UDP probes. However, the procedure is equally applicable to 629 other implementation of traceroute mechanism. 631 Consider the same example where the user wants to traceroute to a 632 remote SID function A4::C52 , via A2::C31, from node N1. 634 o Node N1 initiates a traceroute probe with SRH as follows 635 (B1::0,A2::C31)(A4::C52, A2::C31; HC=64, SL=1, Flags.O=1; 636 NH=UDP)(Traceroute Probe). Please note that the hop-count is set 637 to 64 to skip the underlay nodes from tracing. The O-bit in SRH 638 is set to make the overlay nodes (nodes processing the SRH) 639 respond. 641 o When node N2 receives the packet (B1::0, A2::C31)(A4::C52,A2::C31; 642 SL=1, HC=64, Flags.O=1; NH=UDP)(Traceroute Probe), it processes 643 the O-bit in SRH, as described in the pseudocode in 644 [I-D.filsfils-spring-srv6-network-programming]. A time-stamped 645 copy of the packet gets punted to the traceroute process for 646 processing. Node N2 continues to apply the A2::C31 SID function on 647 the original packet and forwards it, accordingly. As 648 SRH.Flags.O=1, Node N2 also disables the PSP flavor, i.e., does 649 not remove the SRH. The traceroute process at node N2 checks if 650 its local SID (A2::C31) is locally programmed. If the SID is not 651 locally programmed, it silently drops the packet. Otherwise, it 652 performs the egress check by looking at the SL value in SRH. 654 o As SL is not equal to zero (i.e., it's not egress node), node N2 655 responses with the ICMPv6 message (Type: "SRv6 OAM (TBA1 by 656 IANA)", Code: "O-bit punt at Transit (TBA3 by IANA)"). Note that, 657 as mentioned in [I-D.filsfils-spring-srv6-network-programming], if 658 node N2 does not support the O-bit, it simply ignores it and 659 processes the local SID, A2::C31. 661 o When node N3 receives the packet (B1::0, A4::C52)(A4::C52, 662 A2::C31; SL=0, HC=63, Flags.O=1; NH=UDP)(Traceroute Probe), 663 performs the standard IPv6 processing. Specifically, it forwards 664 the traceroute probe based on DA A4::C52 in the IPv6 header. 665 Please note that there is no hop-count expiration at the transit 666 nodes. 668 o When node N4 receives the packet (B1::0, A4::C52)(A4::C52,A2::C31; 669 SL=0, HC=62, Flags.O=1; NH=UDP)(Traceroute Probe), it processes 670 the O-bit in SRH, as described in the pseudocode in 671 [I-D.filsfils-spring-srv6-network-programming]. A time-stamped 672 copy of the packet gets punted to the traceroute process for 673 processing. The traceroute process at node N4 checks if its local 674 SID (A2::C31) is locally programmed. If the SID is not locally 675 programmed, it silently drops the packet. Otherwise, it performs 676 the egress check by looking at the SL value in SRH. As SL is 677 equal to zero (i.e., N4 is the egress node), node N4 tries to 678 consume the UDP probe. As UDP probe is set to access an invalid 679 port, the node N4 responses with the ICMPv6 message (Type: 680 Destination unreachable, Code: Port Unreachable). 682 Figure 5 displays a sample overlay traceroute output for this 683 example. Please note that the underlay node N3 does not appear in 684 the output. 686 > traceroute srv6 A4::C52 via segment-list A2::C31 688 Tracing the route to SID function A4::C52 690 1 2001:DB8:1:2::21 0.512 msec 0.425 msec 0.374 msec 691 SRH: (A4::C52, A4::OTP, A2::C31; SL=2) 693 2 2001:DB8:3:4::41 0.921 msec 0.816 msec 0.759 msec 694 SRH: (A4::C52, A4::OTP, A2::C31; SL=1) 696 Figure 5: A sample output for overlay traceroute to a SID function 698 4. In-situ OAM Applicability 700 [I-D.brockners-inband-oam-requirements] describes motivation and 701 requirements for In-situ OAM (iOAM). iOAM records operational and 702 telemetry information in the data packet while the packet traverses 703 the network of telemetry domain. iOAM complements out-of-band probe 704 based OAM mechanisms such ICMP ping and traceroute by directly 705 encoding tracing and the other kind of telemetry information to the 706 regular data traffic. 708 [I-D.brockners-inband-oam-transport] describes transport mechanisms 709 for iOAM data including IPv6 and Segment Routing traffic. 710 Furthermore, [I-D.brockners-inband-oam-data] defines information 711 encoding for iOAM data. 713 One of the application of iOAM is to perform inband traceroute. In 714 SRv6 network, iOAM traceroute feature can be used to trace the order 715 set of segment ID executed by SRv6 nodes for packet forwarding along 716 the packet path. This is achieved by recording the node details that 717 the packet traversed in the packet header itself. 719 Another important application of iOAM is to perform delay measurement 720 in anycast server scenarios. Anycast server deployment is commonly 721 seen for redundancy and load balancing purpose. In SRv6 network, 722 iOAM can be used to collect the timestamp from different anycats 723 servers to measure the delay induced by each server within the 724 anycast cluster that helps to provide SLA constrained services. 726 One of the other applications of iOAM is to provide the Proof of 727 Transit (POT). Among other features of iOAM, SRv6 networks can use 728 the POT feature of iOAM to verify that all the function SIDs in SRH 729 have been executed before the packet is delivered to the destination. 730 It can also ensure that the order of execution of the SID function 731 has been consistent with the SRH contents. 733 More details on various applications of iOAM in SRv6 networks will be 734 included in future versions of this document. 736 5. Seamless BFD Applicability 738 [RFC7880] defines Seamless BFD (S-BFD) architecture that simplifies 739 BFD mechanism and enables it to perform path monitoring in a 740 controlled and scalable manner. [RFC7881] describes the procedure to 741 perform continuity check using S-BFD in different environments 742 including IPv6 networks. Section 5.1 of [RFC7881] explains the 743 SBFDInitiator specification and procedure to initiate S-BFD control 744 packet in IP and MPLS network. The specification described for 745 IP-routed S-BFD control packet is also directly applicable to the 746 SRv6 network. 748 S-BFD has a fast bootstrapping capability. Furthermore, in S-BFD, 749 only the ingress is required to keep BFD states; the egress and 750 transit node does not have any knowledge of the BFD session. These 751 attributes of S-BFD make it an excellent candidate for rapid failure 752 detection in the SRv6 network. More details on various S-BFD usage 753 on the SRv6 network will be included in a future version. 755 6. Monitoring of SRv6 Paths 757 In the recent past, network operators are interested in performing 758 network OAM functions in a centralized manner. Various data models 759 like YANG are available to collect data from the network and manage 760 it from a centralized entity. 762 The SR technology enables a centralized OAM entity to perform path 763 monitoring without control plane intervention on monitored nodes. 765 [I-D.ietf-spring-oam-usecase] describes such centralized OAM 766 mechanism. Specifically, it describes a procedure that can be used 767 to perform path continuity check between any nodes within an SR 768 domain from a centralized monitoring system, with minimal or no 769 control plane intervention on the nodes. However, the document 770 focuses on SR networks with MPLS data plane. The same concept is 771 also applicable to the SRv6 networks. This document describes how 772 the concept can be used to perform path monitoring in an SRv6 network 773 as follows. 775 In the reference topology in Figure 1, N100 is the controller 776 implementing an END function A100::. In order to verify a segment 777 list , N100 generates a probe packet with SRH set 778 to (A100::, A4::C52, A2::C31, SL=2). The controller routes the probe 779 packet towards the first segment, which is A2::C31. N2 performs the 780 standard SRH processing and forwards it over link3 with the DA of 781 IPv6 packet set to A4::C52. N4 also performs the normal SRH 782 processing and forwards it over link10 with the DA of IPv6 packet set 783 to A100::. This makes the probe packet loop back to the controller. 785 In our reference topology in Figure 1, N100 uses an IGP protocol like 786 OSPF or ISIS to get the topology view within the IGP domain. N100 787 can also use BGP-LS to get the complete view of an inter-domain 788 topology. In other words, the controller leverages the visibility of 789 the topology to monitor the paths between the various endpoints 790 without control plane intervention required at the monitored nodes. 792 7. Security Considerations 794 This document does not define any new protocol extensions and relies 795 on existing procedures defined for ICMP. This document does not 796 impose any additional security challenges to be considered beyond 797 security considerations described in [RFC4884], [RFC4443], [RFC792] 798 and RFCs that updates these RFCs. 800 8. IANA Considerations 802 This document requests IANA to allocate a new Type for ICMPv6 message 803 for "SRv6 OAM". 805 9. References 807 9.1. Normative References 809 [RFC792] J. Postel, "Internet Control Message Protocol", RFC 792, 810 September 1981. 812 [RFC4443] A. Conta, S. Deering, M. Gupta, Ed., "Internet Control 813 Message Protocol (ICMPv6) for the Internet Protocol 814 Version 6 (IPv6) Specification", RFC 4443, March 2006. 816 [RFC4884] R. Bonica, D. Gan, D. Tappan, C. Pignataro, "Extended ICMP 817 to Support Multi-Part Messages", RFC 4884, April 2007. 819 [RFC5837] A. Atlas, Ed., R. Bonica, Ed., C. Pignataro, Ed., N. Shen, 820 JR. Rivers, "Extending ICMP for Interface and Next-Hop 821 Identification", RFC 5837, April 2010. 823 [RFC7880] C.Pignataro, D.Ward, N.Akiya, M.Bhatia, S.Pallagatti, 824 "Seamless Bidirectional Forwarding Detection (S-BFD)", RFC 825 7880, July 2016. 827 [RFC7881] C.Pignataro, D.Ward, N.Akiya, "Seamless Bidirectional 828 Forwarding Detection (S-BFD) for IPv4, IPv6, and MPLS", 829 RFC 7881 July 2016. 831 [I-D.filsfils-spring-srv6-network-programming] C. Filsfils, et al., 832 "SRv6 Network Programming", 833 draft-filsfils-spring-srv6-network-programming, work in 834 progress. 836 [I-D.6man-segment-routing-header] Previdi, S., Filsfils, et al, 837 "IPv6 Segment Routing Header (SRH)", 838 draft-ietf-6man-segment-routing-header, work in progress. 840 9.2. Informative References 842 [I-D.ietf-spring-oam-usecase] A Scalable and Topology-Aware MPLS 843 Dataplane Monitoring System. R. Geib, C. Filsfils, C. 844 Pignataro, N. Kumar, draft-ietf-spring-oam-usecase, work 845 in progress. 847 [I-D.brockners-inband-oam-data] F. Brockners, et al., "Data Formats 848 for In-situ OAM", draft-brockners-inband-oam-data, work in 849 progress. 851 [I-D.brockners-inband-oam-transport] F.Brockners, at al., 852 "Encapsulations for In-situ OAM Data", 853 draft-brockners-inband-oam-transport, work in progress. 855 [I-D.brockners-inband-oam-requirements] F.Brockners, et al., 856 "Requirements for In-situ OAM", 857 draft-brockners-inband-oam-requirements, work in progress. 859 [I-D.spring-segment-routing-policy] Filsfils, C., et al., "Segment 860 Routing Policy for Traffic Engineering", 861 draft-filsfils-spring-segment-routing-policy, work in 862 progress. 864 10. Acknowledgments 866 To be added. 868 Authors' Addresses 870 Clarence Filsfils 871 Cisco Systems, Inc. 872 Email: cfilsfil@cisco.com 874 Zafar Ali 875 Cisco Systems, Inc. 876 Email: zali@cisco.com 878 Nagendra Kumar 879 Cisco Systems, Inc. 880 Email: naikumar@cisco.com 882 Carlos Pignataro 883 Cisco Systems, Inc. 884 Email: cpignata@cisco.com 886 Faisal Iqbal 887 Cisco Systems, Inc. 888 Email: faiqbal@cisco.com 890 Rakesh Gandhi 891 Cisco Systems, Inc. 892 Canada 893 Email: rgandhi@cisco.com 895 John Leddy 896 Comcast 897 Email: John_Leddy@cable.comcast.com 899 Robert Raszuk 900 Bloomberg LP 901 731 Lexington Ave 902 New York City, NY10022, USA 903 Email: robert@raszuk.net 904 Satoru Matsushima 905 SoftBank 906 Japan 907 Email: satoru.matsushima@g.softbank.co.jp 909 Bart Peirens 910 Proximus 911 Email: bart.peirens@proximus.com 913 Gaurav Naik 914 Drexel University 915 United States of America 916 Email: gn@drexel.edu