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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 SPRING H. Song 3 Internet-Draft Futurewei Technologies 4 Intended status: Standards Track T. Pan 5 Expires: December 16, 2021 BUPT 6 June 14, 2021 8 SRv6 In-situ Active Measurement 9 draft-song-spring-siam-01 11 Abstract 13 This draft describes a data-plane in-band active measurement method 14 for SRv6. A packet containing an SRH uses a flag bit to indicate it 15 is a probing packet. The IOAM header and data are encapsulated in 16 UDP payload. The probing packet originates from a segment source 17 node and terminates at a configured segment endpoint node. Each 18 segment node on the path, when detecting the flag, parses the UDP 19 header and the IOAM header, and adds data to the IOAM node data 20 fields. The method avoids the performance and encapsulation issues 21 for applying IOAM in SRv6 networks. Multiple applications can be 22 supported by the method. 24 Requirements Language 26 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 27 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 28 "OPTIONAL" in this document are to be interpreted as described in BCP 29 14 [RFC2119][RFC8174] when, and only when, they appear in all 30 capitals, as shown here. 32 Status of This Memo 34 This Internet-Draft is submitted in full conformance with the 35 provisions of BCP 78 and BCP 79. 37 Internet-Drafts are working documents of the Internet Engineering 38 Task Force (IETF). Note that other groups may also distribute 39 working documents as Internet-Drafts. The list of current Internet- 40 Drafts is at https://datatracker.ietf.org/drafts/current/. 42 Internet-Drafts are draft documents valid for a maximum of six months 43 and may be updated, replaced, or obsoleted by other documents at any 44 time. It is inappropriate to use Internet-Drafts as reference 45 material or to cite them other than as "work in progress." 47 This Internet-Draft will expire on December 16, 2021. 49 Copyright Notice 51 Copyright (c) 2021 IETF Trust and the persons identified as the 52 document authors. All rights reserved. 54 This document is subject to BCP 78 and the IETF Trust's Legal 55 Provisions Relating to IETF Documents 56 (https://trustee.ietf.org/license-info) in effect on the date of 57 publication of this document. Please review these documents 58 carefully, as they describe your rights and restrictions with respect 59 to this document. Code Components extracted from this document must 60 include Simplified BSD License text as described in Section 4.e of 61 the Trust Legal Provisions and are provided without warranty as 62 described in the Simplified BSD License. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 67 2. In-situ Active Measurement for SRv6 . . . . . . . . . . . . . 3 68 3. Network Operation . . . . . . . . . . . . . . . . . . . . . . 5 69 4. Applications . . . . . . . . . . . . . . . . . . . . . . . . 5 70 5. Probing Packet Type Extension . . . . . . . . . . . . . . . . 6 71 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 72 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 73 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 74 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 75 9.1. Normative References . . . . . . . . . . . . . . . . . . 6 76 9.2. Informative References . . . . . . . . . . . . . . . . . 7 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 79 1. Introduction 81 To support SRv6 network operation, we need various means to collect 82 data and measure the performance of SRv6 network. 83 [I-D.ietf-6man-spring-srv6-oam] provides some mechanisms for SRv6 84 OAM. Some other general methods for performance measurement such as 85 [RFC8762] can also be applied for SRv6. However, these methods have 86 limited data coverage and measurement capability. 88 [I-D.ietf-ippm-ioam-data] supports extensible data collection for 89 user traffic. It is beneficial for SRv6 network monitor and 90 measurement. [I-D.ali-spring-ioam-srv6] proposes to encapsulate IOAM 91 in SRH TLV. However, when applying to user packets, IOAM's overhead 92 may cause packet fragmentation and its processing may affect the 93 packet forwarding throughput. Moreover, due to the extension header 94 limitations asserted by [RFC8200], it is not easy to come up with a 95 scheme to encapsulate the IOAM header and data in other locations in 96 SRv6 user packets. 98 Fortunately, the forwarding behavior in SRv6 networks is determined 99 by the SRH. To conduct in-band measurement, the IOAM header and data 100 do not need to be added to user packets. Instead, they can be 101 encapsulated in an independent packet dedicated for measurement. As 102 long as this packet has the same SRH as the user packet, the data 103 collected can faithfully reflect the user packet's forwarding 104 experience, so the result is similar to that by applying IOAM on SRv6 105 user packets. This approach retains the benefits of in-situ 106 measurement but avoids the aforementioned issues. 108 In this case, the IOAM header and data processing can even be done in 109 slow path, without worrying about delaying the user traffic. Because 110 of this, the potential limitation of the forwarding hardware's header 111 processing capability (e.g., the header parsing depth) is no longer 112 an issue. 114 This SR-based active measurement approach also supports some other 115 applications. For example, it can be used to support network-wide 116 telemetry coverage by using pre-planned paths 117 [I-D.tian-bupt-inwt-mechanism-policy]; it can be used to actively 118 measure the backup paths for SRv6 traffic engineering; and by setting 119 the path end as the path head in SRH, it can naturally support two- 120 way or round-trip measurement. 122 The approach is built on existing protocol components with limited 123 extra requirements. 125 2. In-situ Active Measurement for SRv6 127 As specified by [RFC8754], the Segment Routing Header (SRH) contains 128 an 8-bit "Flags" field. This document defines the following flag bit 129 'T' to designate the packet as a dedicated probing packet for active 130 measurement. 132 0 1 2 3 4 5 6 7 133 +-+-+-+-+-+-+-+-+ 134 | |T| | 135 +-+-+-+-+-+-+-+-+ 137 Figure 1: A Hierarchical Edge Network 139 The O-bit defined in [I-D.ietf-6man-spring-srv6-oam] servers for user 140 traffic OAM, so the T-bit and O-bit are mutual exclusive. When T-bit 141 is set, O-bit must be cleared, and vice versa. 143 The Next Header of SRH is set to UDP. A destination UDP port is 144 reserved to further verify this packet is an active probing packet 145 and the UDP payload encapsulates the IOAM header and data as 146 specified in [I-D.ietf-ippm-ioam-data]. The source UDP port can be 147 used as sequence number to track the probing packets on a specific SR 148 path. 150 The complete active probing packet format is shown in Figure 2. 152 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 153 |Ver (6)| Traffic Class | Flow Label | ^ 154 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 155 | Payload Length | NH : SRH | Hop Limit | | 156 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 157 | Source Address (128 bits) | RFC8200 158 | + | 159 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 160 | Destination Address (128 bits) | | 161 | | V 162 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 163 | NH : UDP | Hdr Ext Len | Routing Type | Segments Left | ^ 164 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 165 | Last Entry | |1| Flags | Tag | | 166 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ RFC8754 167 | | | 168 | Segment List (m * 128 bits) | | 169 | | | 170 | | V 171 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 172 | Source Port | Destination Port (TBD) | ^ 173 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ RFC768 174 | Length | Checksum | V 175 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 176 | Namespace-ID |NodeLen | Flags | RemainingLen| ^ 177 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 178 | IOAM-Trace-Type | Reserved | | 179 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IOAM 180 | | | 181 | Node Data List (n * 32 bits) | | 182 | | | 183 | | V 184 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 186 Figure 2: The active probing packet format 188 3. Network Operation 190 The SR source node constructs the probing packets. The source 191 address is the address of the SR source node and the destination 192 address is the address of first SR segment endpoint node. The SRH 193 lists all the SR segment endpoint nodes for which IOAM data will be 194 collected. 196 Each SR node on the path, when detecting the T-flag, in addition to 197 normal SRH processing, will further parse the UDP header and IOAM 198 header, and as directed by the IOAM header, add data to the IOAM node 199 data list. 201 The last SR segment endpoint node will terminate the probing packet. 202 The collected data can be exported and analyzed according to 203 configuration. 205 If an SR segment endpoint node on the path is incapable of processing 206 the probing packet, it should ignore the T-flag and continue 207 forwarding the packet. 209 4. Applications 211 This section summarizes a list of applications of the SRv6 In-situ 212 Active Measurement (SIAM) approach. 214 o As described in Section 1, this is an easy way to apply IOAM in 215 SRv6. In order to collect the on-path data for a specific flow, 216 all we need is to copy the SRH from the flow packet and construct 217 the probing packets. The probing packet rate can match the 218 original flow or arbitrarily configured. The edge of the SR 219 domain must terminate the probing packets to avoid leakage. 221 o To support SRv6 traffic engineering, some alternative paths may be 222 pre-computed. It is desirable to measure the performance of these 223 paths so the best path can be picked when a flow is swapped. 224 Since each path can be represented by an SRH, we can construct the 225 probing packets with these SRHs to actively measure their status 226 and performance. 228 o In an SRv6 network, it is easy to conduct round trip measurement 229 by setting the starting node and the end node of a path to the 230 same segment source node, and setting the destination node as an 231 intermediate node on the path. 233 o To collect the network wide telemetry data and gain global 234 visibility within a SRv6 domain, we can apply the algorithm 235 described in [I-D.tian-bupt-inwt-mechanism-policy] to calculate 236 the optimal SR paths, and construct probing packets on these 237 paths. 239 5. Probing Packet Type Extension 241 The same scheme is also suitable for other types of probing packets. 242 For example, The probing packets can carry IOAM E2E option header and 243 data, IOAM DEX option header, and other telemetry headers and data. 244 It is easy to use different reserved UDP port numbers to 245 differentiate the payload types. 247 6. Security Considerations 249 7. IANA Considerations 251 An SRH Flag bit 'T'. The bit position TBD 253 Optional UDP destination port numbers indicating different IOAM 254 options (TBD) 256 8. Acknowledgments 258 9. References 260 9.1. Normative References 262 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 263 Requirement Levels", BCP 14, RFC 2119, 264 DOI 10.17487/RFC2119, March 1997, 265 . 267 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 268 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 269 May 2017, . 271 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 272 (IPv6) Specification", STD 86, RFC 8200, 273 DOI 10.17487/RFC8200, July 2017, 274 . 276 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 277 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 278 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 279 . 281 9.2. Informative References 283 [I-D.ali-spring-ioam-srv6] 284 Ali, Z., Gandhi, R., Filsfils, C., Brockners, F., Nainar, 285 N., Pignataro, C., Li, C., Chen, M., and G. Dawra, 286 "Segment Routing Header encapsulation for In-situ OAM 287 Data", draft-ali-spring-ioam-srv6-03 (work in progress), 288 November 2020. 290 [I-D.ietf-6man-spring-srv6-oam] 291 Ali, Z., Filsfils, C., Matsushima, S., Voyer, D., and M. 292 Chen, "Operations, Administration, and Maintenance (OAM) 293 in Segment Routing Networks with IPv6 Data plane (SRv6)", 294 draft-ietf-6man-spring-srv6-oam-10 (work in progress), 295 April 2021. 297 [I-D.ietf-ippm-ioam-data] 298 Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields 299 for In-situ OAM", draft-ietf-ippm-ioam-data-12 (work in 300 progress), February 2021. 302 [I-D.tian-bupt-inwt-mechanism-policy] 303 Pan, T., Gao, M., Song, E., Bian, Z., and X. Lin, "In-band 304 Network-Wide Telemetry", draft-tian-bupt-inwt-mechanism- 305 policy-01 (work in progress), October 2020. 307 [RFC8762] Mirsky, G., Jun, G., Nydell, H., and R. Foote, "Simple 308 Two-Way Active Measurement Protocol", RFC 8762, 309 DOI 10.17487/RFC8762, March 2020, 310 . 312 Authors' Addresses 314 Haoyu Song 315 Futurewei Technologies 316 Santa Clara 317 USA 319 Email: haoyu.song@futurewei.com 321 Tian Pan 322 BUPT 323 Beijing 324 China 326 Email: pan@bupt.edu.cn