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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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-17) exists of draft-ietf-ippm-ioam-data-04 == Outdated reference: A later version (-28) exists of draft-ietf-sfc-multi-layer-oam-01 -- Possible downref: Non-RFC (?) normative reference: ref. 'IEEE1588v2' Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IPPM Working Group X. Min 3 Internet-Draft G. Mirsky 4 Intended status: Standards Track ZTE 5 Expires: September 9, 2019 L. Bo 6 China Telecom 7 March 8, 2019 9 Echo Request/Reply for In-situ OAM Capabilities 10 draft-xiao-ippm-ioam-conf-state-03 12 Abstract 14 This document describes an extension to the echo request/reply 15 mechanisms used in MPLS LSP, SRv6, and SFC environments, which can be 16 used within an IOAM domain, allowing the IOAM encapsulating node to 17 acquire IOAM capabilities of each IOAM transit node and/or IOAM 18 decapsulating node. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at https://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on September 9, 2019. 37 Copyright Notice 39 Copyright (c) 2019 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (https://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 55 1.1. Conventions Used in This Document . . . . . . . . . . . . 3 56 1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 57 1.1.2. Requirements Language . . . . . . . . . . . . . . . . 4 58 2. IOAM Capabilities Formats . . . . . . . . . . . . . . . . . . 4 59 2.1. IOAM Capabilities TLV in Echo Request . . . . . . . . . . 4 60 2.2. IOAM Capabilities TLV in Echo Reply . . . . . . . . . . . 5 61 2.2.1. IOAM Pre-allocated Tracing Capabilities sub-TLV . . . 6 62 2.2.2. IOAM Incremental Tracing Capabilities sub-TLV . . . . 7 63 2.2.3. IOAM Proof of Transit Capabilities sub-TLV . . . . . 8 64 2.2.4. IOAM Edge-to-Edge Capabilities sub-TLV . . . . . . . 9 65 2.2.5. IOAM End-of-Domain sub-TLV . . . . . . . . . . . . . 11 66 3. Operational Guide . . . . . . . . . . . . . . . . . . . . . . 11 67 4. Security Considerations . . . . . . . . . . . . . . . . . . . 12 68 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 69 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 70 7. Normative References . . . . . . . . . . . . . . . . . . . . 12 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 73 1. Introduction 75 The Data Fields for In-situ OAM (IOAM) [I-D.ietf-ippm-ioam-data] 76 defines data fields for IOAM which records OAM information within the 77 packet while the packet traverses a particular network domain, which 78 is called an IOAM domain. IOAM can be used to complement OAM 79 mechanisms based on, e.g., ICMP or other types of probe packets, and 80 IOAM mechanisms can be leveraged where mechanisms using, e.g., ICMP 81 do not apply or do not offer the desired results. 83 As specified in [I-D.ietf-ippm-ioam-data], within the IOAM-domain, 84 the IOAM data may be updated by network nodes that the packet 85 traverses. The device which adds an IOAM data container to the 86 packet to capture IOAM data is called the "IOAM encapsulating node", 87 whereas the device which removes the IOAM data container is referred 88 to as the "IOAM decapsulating node". Nodes within the domain which 89 are aware of IOAM data and read and/or write or process the IOAM data 90 are called "IOAM transit nodes". Both the IOAM encapsulating node 91 and the decapsulating node are referred to as domain edge devices, 92 which can be hosts or network devices. 94 In order to add accurate IOAM data container to the packet, the IOAM 95 encapsulating node needs to know IOAM capabilities at the IOAM 96 transit nodes and/or the IOAM decapsulating node as a whole, e.g., 97 how many IOAM transit nodes will add tracing data and what kinds of 98 data fields will be added. 100 This document describes an extension to the echo request/reply 101 mechanisms used in MPLS LSP, SRv6, and SFC environments, which can be 102 used within an IOAM domain, allowing the IOAM encapsulating node to 103 acquire IOAM capabilities of each IOAM transit node and/or IOAM 104 decapsulating node. 106 The following documents contain references to the echo request/reply 107 mechanisms used in MPLS LSP, SRv6, and SFC environments: 109 o [RFC8029] ("Detecting Multiprotocol Label Switched (MPLS) Data- 110 Plane Failures") 112 o [I-D.ali-spring-srv6-oam] ("Operations, Administration, and 113 Maintenance (OAM) in Segment Routing Networks with IPv6 Data plane 114 (SRv6)") 116 o [I-D.ietf-sfc-multi-layer-oam] ("Active OAM for Service Function 117 Chains in Networks") 119 The feature described in this document is assumedly applied to 120 explicit path (strict or loose), because the precondition for this 121 feature to work is that the echo request reaches each IOAM transit 122 node as live traffic traverses. 124 1.1. Conventions Used in This Document 126 1.1.1. Terminology 128 E2E: Edge to Edge 130 ICMP: Internet Control Message Protocol 132 IOAM: In-situ Operations, Administration, and Maintenance 134 LSP: Label Switched Path 136 MPLS: Multi-Protocol Label Switching 138 MBZ: Must Be Zero 140 MTU: Maximum Transmission Unit 142 NTP: Network Time Protocol 144 OAM: Operations, Administration, and Maintenance 145 POSIX: Portable Operating System Interface 147 POT: Proof of Transit 149 PTP: Precision Time Protocol 151 SFC: Service Function Chain 153 SRv6: Segment Routing with IPv6 Data plane 155 TTL: Time to Live 157 1.1.2. Requirements Language 159 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 160 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 161 "OPTIONAL" in this document are to be interpreted as described in BCP 162 14 [RFC2119] [RFC8174] when, and only when, they appear in all 163 capitals, as shown here. 165 2. IOAM Capabilities Formats 167 2.1. IOAM Capabilities TLV in Echo Request 169 In echo request IOAM Capabilities uses TLV (Type-Length-Value tuple) 170 which have the following format: 172 0 1 2 3 173 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 1 174 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 175 | Type = IOAM Capabilities | Length | 176 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 177 | Namespace-IDs Length | MBZ | 178 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 179 . . 180 . List of Namespace-IDs . 181 . . 182 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 184 Figure 1: IOAM Capabilities TLV in Echo Request 186 When this TLV is present in the echo request sent by an IOAM 187 encapsulating node, it means that the IOAM encapsulating node 188 requests the receiving node to reply with its IOAM capabilities. If 189 there is no IOAM capability to be reported by the receiving node, 190 then this TLV SHOULD be ignored by the receiving node, which means 191 the receiving node SHOULD send echo reply without IOAM capabilities 192 or no echo reply, in the light of whether the echo request includes 193 other TLV than IOAM Capabilities TLV. List of Namespace-IDs MAY be 194 included in this TLV of echo request, it means that the IOAM 195 encapsulating node requests only the IOAM capabilities which matches 196 one of the Namespace-IDs. The Namespace-ID has the same definition 197 as what's specified in [I-D.ietf-ippm-ioam-data]. 199 Type is set to the value which indicates that it's an IOAM 200 Capabilities TLV. 202 Length is the length of the TLV's Value field in octets, Namespace- 203 IDs Length is the Length of the List of Namespace-IDs field in 204 octets. 206 Value field of this TLV is zero padded to align to a 4-octet 207 boundary. 209 2.2. IOAM Capabilities TLV in Echo Reply 211 In echo reply IOAM Capabilities uses TLV which have the following 212 format: 214 0 1 2 3 215 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 1 216 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 217 | Type = IOAM Capabilities | Length | 218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 219 | Sub-TLVs Length | MBZ | 220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 221 . . 222 . List of Sub-TLVs . 223 . . 224 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 226 Figure 2: IOAM Capabilities TLV in Echo Reply 228 When this TLV is present in the echo reply sent by an IOAM transit 229 node and/or an IOAM decapsulating node, it means that IOAM function 230 is enabled at this node and this TLV contains IOAM capabilities of 231 the sender. List of Sub-TLVs which contain the IOAM capabilities 232 SHOULD be included in this TLV of the echo reply. Note that the IOAM 233 encapsulating node or the IOAM decapsulating node can also be an IOAM 234 transit node. 236 Type is set to the value which indicates that it's an IOAM 237 Capabilities TLV. 239 Length is the length of the TLV's Value field in octets, Sub-TLVs 240 Length is the length of the List of Sub-TLVs field in octets. 242 Value field of this TLV or any Sub-TLV is zero padded to align to a 243 4-octet boundary. Based on the data fields for IOAM specified in 244 [I-D.ietf-ippm-ioam-data], five kinds of Sub-TLVs are defined in this 245 document, and in an IOAM Capabilities TLV the same kind of Sub-TLV 246 can appear more times than one with different Namespace-ID. Note 247 that the IOAM encapsulating node may receive both IOAM Pre-allocated 248 Tracing Capabilities sub-TLV and IOAM Incremental Tracing 249 Capabilities sub-TLV in the process of traceroute, which means both 250 pre-allocated tracing node and incremental tracing node are on the 251 same path, or some node supports both pre-allocated tracing and 252 incremental tracing, the behavior of the IOAM encapsulating node in 253 this scenario is outside the scope of this document. 255 2.2.1. IOAM Pre-allocated Tracing Capabilities sub-TLV 257 0 1 2 3 258 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 1 259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 260 |Sub-type = Pre-allocated trace | Length | 261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 262 | IOAM-Trace-Type | Reserved | 263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 264 | Namespace-ID | Egress_MTU | 265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 266 | Egress_if_id (short or wide format) ...... | 267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 269 Figure 3: IOAM Pre-allocated Tracing Capabilities Sub-TLV 271 When this sub-TLV is present in the IOAM Capabilities TLV, it means 272 that the sending node is an IOAM transit node and IOAM tracing 273 function is enabled at this IOAM transit node. 275 Sub-type is set to the value which indicates that it's an IOAM Pre- 276 allocated Tracing Capabilities sub-TLV. 278 Length is the length of the sub-TLV's Value field in octets, if 279 Egress_if_id is in the short format which is 16 bits long, it MUST be 280 set to 10, and if Egress_if_id is in the wide format which is 32 bits 281 long, it MUST be set to 12. 283 IOAM-Trace-Type field has the same definition as what's specified in 284 section 4.2 of [I-D.ietf-ippm-ioam-data]. 286 Reserved field is reserved for future use and MUST be set to zero. 288 Namespace-ID field has the same definition as what's specified in 289 section 4.2 of [I-D.ietf-ippm-ioam-data], it should be a one of the 290 Namespace-IDs listed in the IOAM Capabilities TLV of echo request. 292 Egress_MTU field has 16 bits and specifies the MTU of the egress 293 direction out of which the sending node would forward the received 294 echo request, it should be the MTU of the egress interface or the MTU 295 between the sending node and the downstream IOAM transit node. 297 Egress_if_id field has 16 bits (in short format) or 32 bits (in wide 298 format) and specifies the identifier of the egress interface out of 299 which the sending node would forward the received echo request. 301 2.2.2. IOAM Incremental Tracing Capabilities sub-TLV 303 0 1 2 3 304 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 1 305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 306 | Sub-type = Incremental trace | Length | 307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 308 | IOAM-Trace-Type | Reserved | 309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 310 | Namespace-ID | Egress_MTU | 311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 312 | Egress_if_id (short or wide format) ...... | 313 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 315 Figure 4: IOAM Incremental Tracing Capabilities Sub-TLV 317 When this sub-TLV is present in the IOAM Capabilities TLV, it means 318 that the sending node is an IOAM transit node and IOAM tracing 319 function is enabled at this IOAM transit node. 321 Sub-type is set to the value which indicates that it's an IOAM 322 Incremental Tracing Capabilities sub-TLV. 324 Length is the length of the sub-TLV's Value field in octets, if 325 Egress_if_id is in the short format which is 16 bits long, it MUST be 326 set to 10, and if Egress_if_id is in the wide format which is 32 bits 327 long, it MUST be set to 12. 329 IOAM-Trace-Type field has the same definition as what's specified in 330 section 4.2 of [I-D.ietf-ippm-ioam-data]. 332 Reserved field is reserved for future use and MUST be set to zero. 334 Namespace-ID field has the same definition as what's specified in 335 section 4.2 of [I-D.ietf-ippm-ioam-data], it should be a one of the 336 Namespace-IDs listed in the IOAM Capabilities TLV of echo request. 338 Egress_MTU field has 16 bits and specifies the MTU of the egress 339 direction out of which the sending node would forward the received 340 echo request, it should be the MTU of the egress interface or the MTU 341 between the sending node and the downstream IOAM transit node. 343 Egress_if_id field has 16 bits (in short format) or 32 bits (in wide 344 format) and specifies the identifier of the egress interface out of 345 which the sending node would forward the received echo request. 347 2.2.3. IOAM Proof of Transit Capabilities sub-TLV 349 0 1 2 3 350 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 1 351 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 352 | Sub-type = POT Capabilities | Length | 353 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 354 | Namespace-ID | IOAM-POT-Type |P|SoR|Reserved | 355 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 357 Figure 5: IOAM Proof of Transit Capabilities Sub-TLV 359 When this sub-TLV is present in the IOAM Capabilities TLV, it means 360 that the sending node is an IOAM transit node and IOAM proof of 361 transit function is enabled at this IOAM transit node. 363 Sub-type is set to the value which indicates that it's an IOAM Proof 364 of Transit Capabilities sub-TLV. 366 Length is the length of the sub-TLV's Value field in octets, and MUST 367 be set to 4. 369 Namespace-ID field has the same definition as what's specified in 370 section 4.3 of [I-D.ietf-ippm-ioam-data], it should be a one of the 371 Namespace-IDs listed in the IOAM Capabilities TLV of echo request. 373 IOAM-POT-Type field and P bit have the same definition as what's 374 specified in section 4.3 of [I-D.ietf-ippm-ioam-data]. If the IOAM 375 encapsulating node receives IOAM-POT-Type and/or P bit values from an 376 IOAM transit node that are different from its own, then the IOAM 377 encapsulating node MAY choose to abandon the proof of transit 378 function or to select one kind of IOAM-POT-Type and P bit, it's based 379 on the policy applied to the IOAM encapsulating node. 381 SoR field has two bits which means the size of "Random" and 382 "Cumulative" data, which are specified in section 4.3 of 383 [I-D.ietf-ippm-ioam-data]. This document defines SoR as follow: 385 0b00 means 64-bit "Random" and 64-bit "Cumulative" data. 387 0b01~0b11: Reserved for future standardization 389 Reserved field is reserved for future use and MUST be set to zero. 391 2.2.4. IOAM Edge-to-Edge Capabilities sub-TLV 393 0 1 2 3 394 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 1 395 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 396 | Sub-type = E2E Capabilities | Length | 397 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 398 | Namespace-ID | IOAM-E2E-Type | 399 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 400 |TSF|TSL| Reserved | MBZ | 401 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 403 Figure 6: IOAM Edge-to-Edge Capabilities Sub-TLV 405 When this sub-TLV is present in the IOAM Capabilities TLV, it means 406 that the sending node is an IOAM decapsulating node and IOAM edge-to- 407 edge function is enabled at this IOAM decapsulating node. That is to 408 say, if the IOAM encapsulating node receives this sub-TLV, the IOAM 409 encapsulating node can determine that the node which sends this sub- 410 TLV is an IOAM decapsulating node. 412 Sub-type is set to the value which indicates that it's an IOAM Edge- 413 to-Edge Capabilities sub-TLV. 415 Length is the length of the sub-TLV's Value field in octets, and MUST 416 be set to 8. 418 Namespace-ID field has the same definition as what's specified in 419 section 4.4 of [I-D.ietf-ippm-ioam-data], it should be a one of the 420 Namespace-IDs listed in the IOAM Capabilities TLV of echo request. 422 IOAM-E2E-Type field has the same definition as what's specified in 423 section 4.4 of [I-D.ietf-ippm-ioam-data]. 425 TSF field specifies the timestamp format used by the sending node. 426 This document defines TSF as follow: 428 0b00: PTP timestamp format 430 0b01: NTP timestamp format 432 0b10: POSIX timestamp format 434 0b11: Reserved for future standardization 436 TSL field specifies the timestamp length used by the sending node. 437 This document defines TSL as follow: 439 When TSF field is set to 0b00 which indicates PTP timestamp 440 format: 442 0b00: 64-bit PTPv1 timestamp as defined in IEEE1588-2008 443 [IEEE1588v2] 445 0b01: 80-bit PTPv2 timestamp as defined in IEEE1588-2008 446 [IEEE1588v2] 448 0b10~0b11: Reserved for future standardization 450 When TSF field is set to 0b01 which indicates NTP timestamp 451 format: 453 0b00: 32-bit NTP timestamp as defined in NTPv4 [RFC5905] 455 0b01: 64-bit NTP timestamp as defined in NTPv4 [RFC5905] 457 0b10: 128-bit NTP timestamp as defined in NTPv4 [RFC5905] 459 0b11: Reserved for future standardization 461 When TSF field is set to 0b10 or 0b11, the TSL field would be 462 ignored. 464 Reserved field is reserved for future use and MUST be set to zero. 466 2.2.5. IOAM End-of-Domain sub-TLV 468 0 1 2 3 469 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 1 470 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 471 | Sub-type = End of Domain | Length | 472 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 473 | Namespace-ID | MBZ | 474 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 476 Figure 7: IOAM End of Domain Sub-TLV 478 When this sub-TLV is present in the IOAM Capabilities TLV, it means 479 that the sending node is an IOAM decapsulating node. That is to say, 480 if the IOAM encapsulating node receives this sub-TLV, the IOAM 481 encapsulating node can determine that the node which sends this sub- 482 TLV is an IOAM decapsulating node. When the IOAM Edge-to-Edge 483 Capabilities sub-TLV is present in the IOAM Capabilities TLV sent by 484 the IOAM decapsulating node, the IOAM End-of-Domain sub-TLV doesn't 485 need to be present in the same IOAM Capabilities TLV, otherwise the 486 End-of-Domain sub-TLV MUST be present in the IOAM Capabilities TLV 487 sent by the IOAM decapsulating node. Since both the IOAM Edge-to- 488 Edge Capabilities sub-TLV and the IOAM End-of-Domain sub-TLV can be 489 used to indicate that the sending node is an IOAM decapsulating node, 490 it's recommended to include only the IOAM Edge-to-Edge Capabilities 491 sub-TLV if IOAM edge-to-edge function is enabled at this IOAM 492 decapsulating node. 494 Length is the length of the sub-TLV's Value field in octets, and MUST 495 be set to 4. 497 Namespace-ID field has the same definition as what's specified in 498 section 4.4 of [I-D.ietf-ippm-ioam-data], it should be a one of the 499 Namespace-IDs listed in the IOAM Capabilities TLV of echo request. 501 3. Operational Guide 503 Once the IOAM encapsulating node is triggered to acquire IOAM 504 capabilities of each IOAM transit node and/or IOAM decapsulating 505 node, the IOAM encapsulating node will send a batch of echo requests 506 that include the IOAM Capabilities TLV, first with TTL equal to 1 to 507 reach the nearest node which may be an IOAM transit node or not, then 508 with TTL equal to 2 to reach the second nearest node which also may 509 be an IOAM transit node or not, on the analogy of this to increase 1 510 to TTL every time the IOAM encapsulating node sends a new echo 511 request, until the IOAM encapsulating node receives echo reply sent 512 by the IOAM decapsulating node, which should contain the IOAM 513 Capabilities TLV including the IOAM Edge-to-Edge Capabilities sub-TLV 514 or the IOAM End-of-Domain sub-TLV. Alternatively, if the IOAM 515 encapsulating node knows exactly all the IOAM transit nodes and/or 516 IOAM decapsulating node beforehand, once the IOAM encapsulating node 517 is triggered to acquire IOAM capabilities, it can send echo request 518 to each IOAM transit node and/or IOAM decapsulating node directly, 519 without TTL expiration. 521 The IOAM encapsulating node may be triggered by the device 522 administrator, the network management system, the network controller, 523 or even the live user traffic, and the specific triggering mechanisms 524 are outside the scope of this document. 526 Each IOAM transit node and/or IOAM decapsulating node that receives 527 an echo request containing the IOAM Capabilities TLV will send an 528 echo reply to the IOAM encapsulating node, and within the echo reply, 529 there should be an IOAM Capabilities TLV containing one or more sub- 530 TLVs. The IOAM Capabilities TLV contained in the echo request would 531 be ignored by the receiving node that is unaware of IOAM. 533 4. Security Considerations 535 Knowledge of the state of the IOAM domain may be considered 536 confidential. Implementations SHOULD provide a means of filtering 537 the addresses to which echo request/reply may be sent. 539 5. IANA Considerations 541 This document has no IANA actions. 543 6. Acknowledgements 545 The authors would like to acknowledge Tianran Zhou for his careful 546 review and helpful comments. 548 The authors appreciate the f2f discussion with Frank Brockners on 549 this document. 551 7. Normative References 553 [I-D.ali-spring-srv6-oam] 554 Ali, Z., Filsfils, C., Kumar, N., Pignataro, C., 555 faiqbal@cisco.com, f., Gandhi, R., Leddy, J., Matsushima, 556 S., Raszuk, R., daniel.voyer@bell.ca, d., Dawra, G., 557 Peirens, B., Chen, M., and G. Naik, "Operations, 558 Administration, and Maintenance (OAM) in Segment Routing 559 Networks with IPv6 Data plane (SRv6)", draft-ali-spring- 560 srv6-oam-02 (work in progress), October 2018. 562 [I-D.ietf-ippm-ioam-data] 563 Brockners, F., Bhandari, S., Pignataro, C., Gredler, H., 564 Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov, 565 P., Chang, R., daniel.bernier@bell.ca, d., and J. Lemon, 566 "Data Fields for In-situ OAM", draft-ietf-ippm-ioam- 567 data-04 (work in progress), October 2018. 569 [I-D.ietf-sfc-multi-layer-oam] 570 Mirsky, G., Meng, W., Khasnabish, B., and C. Wang, "Active 571 OAM for Service Function Chains in Networks", draft-ietf- 572 sfc-multi-layer-oam-01 (work in progress), January 2019. 574 [IEEE1588v2] 575 Institute of Electrical and Electronics Engineers, "IEEE 576 Std 1588-2008 - IEEE Standard for a Precision Clock 577 Synchronization Protocol for Networked Measurement and 578 Control Systems", IEEE Std 1588-2008, 2008, 579 . 582 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 583 Requirement Levels", BCP 14, RFC 2119, 584 DOI 10.17487/RFC2119, March 1997, 585 . 587 [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, 588 "Network Time Protocol Version 4: Protocol and Algorithms 589 Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010, 590 . 592 [RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N., 593 Aldrin, S., and M. Chen, "Detecting Multiprotocol Label 594 Switched (MPLS) Data-Plane Failures", RFC 8029, 595 DOI 10.17487/RFC8029, March 2017, 596 . 598 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 599 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 600 May 2017, . 602 Authors' Addresses 604 Xiao Min 605 ZTE 606 Nanjing 607 China 609 Phone: +86 25 88016574 610 Email: xiao.min2@zte.com.cn 612 Greg Mirsky 613 ZTE 614 USA 616 Email: gregimirsky@gmail.com 618 Lei Bo 619 China Telecom 620 Beijing 621 China 623 Phone: +86 10 50902903 624 Email: leibo.bri@chinatelecom.cn