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Song, Ed. 3 Internet-Draft Futurewei Technologies 4 Intended status: Standards Track October 14, 2019 5 Expires: April 16, 2020 7 Support Postcard-Based Telemetry for SRv6 OAM 8 draft-song-6man-srv6-pbt-01 10 Abstract 12 Applications such as SRv6 TE may require to collect detailed 13 performance data on SR paths. Existing in-situ OAM techniques incur 14 encapsulation and header overhead issues. This document describes a 15 method based on Postcard-based Telemetry with Packet Marking for SRv6 16 on-path OAM, which avoids the extra overhead for encapsulating 17 telemetry-related instruction and metadata in SRv6 packets. 19 Requirements Language 21 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 22 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 23 "OPTIONAL" in this document are to be interpreted as described in BCP 24 14 [RFC2119][RFC8174] when, and only when, they appear in all 25 capitals, as shown here. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at https://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on April 16, 2020. 44 Copyright Notice 46 Copyright (c) 2019 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (https://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 62 2. PBT Triggered by Marking for SRv6 . . . . . . . . . . . . . . 3 63 2.1. Data Template . . . . . . . . . . . . . . . . . . . . . . 3 64 2.2. Postcard Correlation . . . . . . . . . . . . . . . . . . 4 65 2.3. Operational Considerations . . . . . . . . . . . . . . . 4 66 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4 67 4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 68 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 69 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 5 70 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5 71 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 72 8.1. Normative References . . . . . . . . . . . . . . . . . . 5 73 8.2. Informative References . . . . . . . . . . . . . . . . . 5 74 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6 76 1. Introduction 78 The ability to collect the on-path data about SRv6 packets at each 79 segment is important for SRv6 OAM, especially for monitoring the 80 application-aware services. Some SR-TE algorithms need to acquire 81 realtime flow forwarding performance on each path. The In-situ OAM 82 (IOAM) [I-D.ietf-ippm-ioam-data] trace option can be used for such 83 purpose. However, SRv6's SRH can be large due to the long segment 84 list. The IOAM trace option introduces significant additional 85 overhead to the SRv6 packets with its instruction and data trace. 86 The large header overhead complicates the packet processing and may 87 exceed the forwarding hardware's header processing capability. 89 The extra IOAM trace option header also brings encapsulation 90 challenges as documented in [I-D.li-6man-ipv6-sfc-ifit]. Here we 91 only restate a subtle issue about the IOAM scope: if IOAM header is 92 encapsulated as another IPv6 extension header, the juxtaposition of 93 IOAM and SRH makes it ambiguous to determine the scope and coverage 94 of IOAM: it is unclear if the IOAM is applied to the entire 95 forwarding path or just to the segment nodes. In reality, either 96 case can find its application. 98 The Direct EXport (DEX) option of IOAM described in 99 [I-D.ioamteam-ippm-ioam-direct-export] partially relieves the packet 100 overhead pressure by avoiding including trace data in SRv6 packet, 101 but the encapsulation issue remains, so does the aforementioned 102 ambiguirty. In this document, we propose to apply the PBT-M scheme 103 from [I-D.song-ippm-postcard-based-telemetry] for on-path SRv6 104 telemetry, which can help to solve the encapsulation and overhead 105 issues. 107 2. PBT Triggered by Marking for SRv6 109 PBT-M requires marking a packet as a trigger to collect on-path data 110 about the packet. The collected data are exported by an independent 111 "postcard" packet. Therefore, there is no new header encapsulation 112 requirement. 114 Eight flag bits are currently reserved in SRH. One of those bits can 115 be used as the marking flag, as shown in the following figure. If 116 the "T"-bit is set to 1, the segment node which process the SRH needs 117 to export the on-path data about this packet as pre-configured 118 through management interface. 120 0 1 2 3 121 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 1 122 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 123 | Next Header | Hdr Ext Len | Routing Type | Segments Left | 124 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 125 | Last Entry |T| Flags | Tag | 126 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 127 | | 128 | | 129 ~ Segment List[] & TLV ~ 130 | | 131 | | 132 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 134 Figure 1: SRH with PBT Mark Flag 136 2.1. Data Template 138 It is possible to have the same configuration for all the segment 139 nodes on the data set to collect. However, different flows may 140 require different data collection profiles. It would be more 141 flexible to have multiple different data templates supported by the 142 segment nodes and each packet can designate one template that best 143 suits its interests to use. The template ID can be carried as a TLV 144 in SRH. 146 2.2. Postcard Correlation 148 As discussed in [I-D.song-ippm-postcard-based-telemetry], PBT-M has 149 some issues to correlate the postcards from the different segment 150 nodes for the same user packet. While several solutions are given to 151 mitigate the problem, it is ideal to be able to correlate the 152 postcards without any constraint and precondition. 154 A flow ID and a sequence number can be included as TLVs in SRH. The 155 format and usage of the flow ID and the sequence number are the same 156 as those in IOAM DEX option in 157 [I-D.ioamteam-ippm-ioam-direct-export]. Further, the exported 158 postcard may include the SRH or the current SID which provides a 159 trace to order the postcards. 161 2.3. Operational Considerations 163 The SR source node is responsible to determine the policy for setting 164 or resetting the "T"-bit. 166 A segment node can decide independently whether or not to react on 167 the "T"-bit. 169 3. Use Cases 171 TBD. 173 4. Security Considerations 175 Since PBT incurs some extra packet processing and transport cost, "T" 176 flag is usually selectively set on a subset of packets by the source 177 node. A potential DoS attack may set the "T" flag for all the packet 178 with the intention to overwhelm the segment nodes. Therefore, the 179 postcards should be generated on the basis of the best effort. 181 5. IANA Considerations 183 [I-D.ietf-6man-segment-routing-header] defines a new registry named 184 "Segment Routing Header Flags". This document requests the 185 allocation of a new flag bit "T" for the telemetry trigger mark. 187 6. Contributors 189 TBD. 191 7. Acknowledgments 193 TBD. 195 8. References 197 8.1. Normative References 199 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 200 Requirement Levels", BCP 14, RFC 2119, 201 DOI 10.17487/RFC2119, March 1997, 202 . 204 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 205 Writing an IANA Considerations Section in RFCs", BCP 26, 206 RFC 8126, DOI 10.17487/RFC8126, June 2017, 207 . 209 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 210 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 211 May 2017, . 213 8.2. Informative References 215 [I-D.ietf-6man-segment-routing-header] 216 Filsfils, C., Dukes, D., Previdi, S., Leddy, J., 217 Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment 218 Routing Header (SRH)", draft-ietf-6man-segment-routing- 219 header-24 (work in progress), October 2019. 221 [I-D.ietf-ippm-ioam-data] 222 Brockners, F., Bhandari, S., Pignataro, C., Gredler, H., 223 Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov, 224 P., Chang, R., daniel.bernier@bell.ca, d., and J. Lemon, 225 "Data Fields for In-situ OAM", draft-ietf-ippm-ioam- 226 data-07 (work in progress), September 2019. 228 [I-D.ioamteam-ippm-ioam-direct-export] 229 Song, H., Gafni, B., Zhou, T., Li, Z., Brockners, F., 230 Bhandari, S., Sivakolundu, R., and T. Mizrahi, "In-situ 231 OAM Direct Exporting", draft-ioamteam-ippm-ioam-direct- 232 export-00 (work in progress), October 2019. 234 [I-D.li-6man-ipv6-sfc-ifit] 235 Li, Z., Peng, S., and K. LEE, "IPv6 Encapsulation for SFC 236 and IFIT", draft-li-6man-ipv6-sfc-ifit-02 (work in 237 progress), September 2019. 239 [I-D.song-ippm-postcard-based-telemetry] 240 Song, H., Zhou, T., Li, Z., Shin, J., and K. Lee, 241 "Postcard-based On-Path Flow Data Telemetry", draft-song- 242 ippm-postcard-based-telemetry-05 (work in progress), 243 September 2019. 245 Author's Address 247 Haoyu Song (editor) 248 Futurewei Technologies 249 2330 Central Expressway 250 Santa Clara 251 USA 253 Email: hsong@futurewei.com