6man H. Song, Ed. Internet-Draft Futurewei Technologies Intended status: Standards Track July 1, 2019 Expires: January 2, 2020 Support Postcard-Based Telemetry for SRv6 OAM draft-song-6man-srv6-pbt-00 Abstract This document describes a method based on Postcard-based Telemetry with Marking for SRv6 on-path OAM, which avoids the extra overhead for encapsulating telemetry-related instruction and metadata in SRv6 packets. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119][RFC8174] when, and only when, they appear in all capitals, as shown here. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on January 2, 2020. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents Song Expires January 2, 2020 [Page 1] Internet-Draft PBT for SRv6 OAM July 2019 (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. PBT Triggered by Marking for SRv6 . . . . . . . . . . . . . . 3 2.1. Data Template . . . . . . . . . . . . . . . . . . . . . . 3 2.2. Postcard Correlation . . . . . . . . . . . . . . . . . . 3 2.3. Operational Considerations . . . . . . . . . . . . . . . 4 3. Security Considerations . . . . . . . . . . . . . . . . . . . 4 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 4 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 4 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 7.1. Normative References . . . . . . . . . . . . . . . . . . 4 7.2. Informative References . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction The ability to collect the on-path data about SRv6 packets at each segment is important for SRv6 OAM, especially for monitoring the application-aware services. The In-situ OAM (IOAM) [I-D.brockners-inband-oam-data] trace option can be used for such purpose. However, SRv6's SRH can be large due to the long segment list. The IOAM trace option introduces significant additional overhead to the SRv6 packets with its instruction and data trace. The large header overhead complicates the packet processing and may exceed the forwarding hardware's header processing capability. The extra IOAM trace option header also brings some encapsulation challenges as documented in [I-D.li-6man-ipv6-sfc-ifit]. Here we restate a subtle issue about the IOAM scope: if IOAM header is encapsulated as another IPv6 extension header, the juxtaposition of IOAM and SRH makes it ambiguous to determine the coverage of IOAM: should it be applied to the entire forwarding path or just to the segment nodes? The PBT-I scheme introduced in [I-D.song-ippm-postcard-based-telemetry] partially relieves the packet overhead pressure but the encapsulation issues remain. In Song Expires January 2, 2020 [Page 2] Internet-Draft PBT for SRv6 OAM July 2019 this draft, we propose to apply the PBT-M scheme from the same document for on-path SRv6 telemetry. 2. PBT Triggered by Marking for SRv6 PBT-M requires marking a packet as a trigger to collect on-path data about the packet. The collected data are exported by an independent "postcard" packet. Therefore, there is no new header encapsulation requirement. Eight flag bits are currently reserved in SRH. One of those bits can be used as the marking flag, as shown in the following figure. If the "T"-bit is set to 1, the segment node which process the SRH needs to export the on-path data about this packet as configured. 0 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len | Routing Type | Segments Left | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Last Entry |T| Flags | Tag | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | ~ Segment List[] & TLV ~ | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: SRH with PBT Mark Flag 2.1. Data Template Although it is possible to configure the segment nodes about the data set to collect, different flows may require different data collection profiles. It would be more flexible to have multiple different data templates supported by the segment nodes and each packet can designate one template that best suits its interests to use. The template ID can be carried as a TLV in SRH. 2.2. Postcard Correlation As discussed in [I-D.song-ippm-postcard-based-telemetry], PBT-M has some issues to correlate the postcards from the different segment nodes for the same user packet. While several solutions are given to Song Expires January 2, 2020 [Page 3] Internet-Draft PBT for SRv6 OAM July 2019 mitigate the problem, it is ideal to be able to correlate the postcards without any constraint and precondition. A flow ID and a sequence number can be included as TLVs in SRH. The specification and usage of the flow ID and the sequence number are the same as those in PBT-I in [I-D.song-ippm-postcard-based-telemetry]. Further, the exported postcard may include the SRH or the current SID which provides a trace to order the postcards. 2.3. Operational Considerations The SR source node is responsible to determine the policy for setting or resetting the "T"-bit. The segment node can decide independently whether or not to react on the "T"-bit. 3. Security Considerations Since PBT incurs some extra packet processing and transport cost, "T" flag is usually selectively set on a subset of packets by the source node. A potential DoS attack may set the "T" flag for all the packet with the intention to overwhelm the segment nodes. Therefore, the postcards should be generated on the basis of the best effort. 4. IANA Considerations [I-D.ietf-6man-segment-routing-header] defines a new registry named "Segment Routing Header Flags". This document requests the allocation of a new flag bit "T" for the telemetry trigger mark. 5. Contributors TBD. 6. Acknowledgments TBD. 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . Song Expires January 2, 2020 [Page 4] Internet-Draft PBT for SRv6 OAM July 2019 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 7.2. Informative References [I-D.brockners-inband-oam-data] Brockners, F., Bhandari, S., Pignataro, C., Gredler, H., Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov, P., Chang, R., and d. daniel.bernier@bell.ca, "Data Fields for In-situ OAM", draft-brockners-inband-oam-data-07 (work in progress), July 2017. [I-D.ietf-6man-segment-routing-header] Filsfils, C., Dukes, D., Previdi, S., Leddy, J., Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header (SRH)", draft-ietf-6man-segment-routing- header-21 (work in progress), June 2019. [I-D.li-6man-ipv6-sfc-ifit] Li, Z. and S. Peng, "Consideration of IPv6 Encapsulation for SFC and IFIT", draft-li-6man-ipv6-sfc-ifit-00 (work in progress), March 2019. [I-D.song-ippm-postcard-based-telemetry] Song, H., Zhou, T., Li, Z., Shin, J., and K. Lee, "Postcard-based On-Path Flow Data Telemetry", draft-song- ippm-postcard-based-telemetry-04 (work in progress), June 2019. Author's Address Haoyu Song (editor) Futurewei Technologies 2330 Central Expressway Santa Clara USA Email: hsong@futurewei.com Song Expires January 2, 2020 [Page 5]