IPPM Z. Li Internet-Draft Z. Du Intended status: Standards Track China Mobile Expires: 5 January 2027 J. Wang W. Cheng G. Zhang Centec X. Sun Inesa C. Zhao SAIA 4 July 2026 Multi-Point Telemetry Correlation for Network Measurement draft-li-ippm-multipoint-telemetry-00 Abstract Network measurement and telemetry systems that collect data at multiple points along a path or across multiple targets require a means to correlate the collected data. When each collection point independently selects which packets to observe, the resulting data sets may not overlap, preventing per-packet correlation of measurements across points. This document specifies how source-directed selection -- where a single node determines which packets are subject to measurement and signals this to other nodes -- achieves correlated data collection across multiple points. Two applications are described: IOAM Direct Export for in-band network telemetry, and PTP Sequence ID range assignment for multi-slave time synchronization. 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." Li, et al. Expires 5 January 2027 [Page 1] Internet-Draft Multi-Point Telemetry July 2026 This Internet-Draft will expire on 5 January 2027. Copyright Notice Copyright (c) 2026 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 (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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Application to IOAM Direct Export . . . . . . . . . . . . . . 3 2.1. Encapsulating Node . . . . . . . . . . . . . . . . . . . 3 2.2. Transit and Decapsulating Nodes . . . . . . . . . . . . . 3 2.3. Data Correlation . . . . . . . . . . . . . . . . . . . . 4 3. Application to PTP Multi-Slave Topologies . . . . . . . . . . 4 3.1. Sequence ID Range Assignment . . . . . . . . . . . . . . 4 3.2. Grandmaster Timestamp Correlation . . . . . . . . . . . . 4 3.3. Slave Processing . . . . . . . . . . . . . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 6. Normative References . . . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction Distributed network measurement systems collect data at multiple points in the network. In forwarding-plane telemetry systems such as IOAM [RFC9197], each node along a packet's path may independently export measurement data. In time synchronization systems such as PTP [IEEE-1588], a Grandmaster may serve multiple slaves, generating timestamped messages that must be correlated with specific targets. Li, et al. Expires 5 January 2027 [Page 2] Internet-Draft Multi-Point Telemetry July 2026 A common challenge in both scenarios is ensuring that data collected at different points corresponds to the same set of packets or the same target. When each collection point independently selects packets for observation (per [RFC5475]), different points may observe different subsets of the same flow, making per-packet path analysis impossible. Similarly, when a time source generates timestamps for multiple targets, each timestamp must be associated with the correct target. This document specifies source-directed selection, in which a single node makes the selection or assignment decision and communicates it to other nodes via in-band signaling. Two specific applications are described in the following sections. 1.1. 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. 2. Application to IOAM Direct Export IOAM Direct Export (DEX) [RFC9326] defines an IOAM Option-Type that triggers each transit node to export telemetry data for a packet without embedding the data in the packet itself. The IOAM encapsulating node selects which packets carry the DEX option, and all downstream nodes export data for those packets. 2.1. Encapsulating Node The IOAM encapsulating node applies a sampling policy (e.g., 1-in-N, probabilistic, or hash-based per [RFC5475]) to monitored flows. Packets selected by the sampling policy are encapsulated with the DEX Option-Type per [RFC9326]. Packets not selected are forwarded without the DEX option. The encapsulating node SHOULD also export its own local telemetry data for each DEX-carrying packet. 2.2. Transit and Decapsulating Nodes IOAM transit nodes export local telemetry data for every packet carrying the DEX option, per [RFC9326]. Transit nodes MUST NOT apply independent sampling decisions to DEX packets; the presence of the DEX option is itself the selection indicator. The IOAM decapsulating node exports its local telemetry data and removes the DEX option before forwarding the packet beyond the IOAM domain. Li, et al. Expires 5 January 2027 [Page 3] Internet-Draft Multi-Point Telemetry July 2026 2.3. Data Correlation Because all nodes on the path export data for the same set of packets, a collector can reconstruct the per-packet experience at each hop. Telemetry records from different nodes for the same packet can be correlated using the flow identifier and a packet-level identifier (e.g., a hash of invariant header fields, or a sequence number from the transport layer). The choice of packet-level identifier is outside the scope of this document. 3. Application to PTP Multi-Slave Topologies The Precision Time Protocol (PTP) [IEEE-1588] supports time synchronization between a Grandmaster and multiple Ordinary Clock slaves. In Two-Step operation, the Grandmaster captures the egress timestamp of each Sync message in hardware and communicates it via a Follow_Up message. When the Grandmaster serves multiple slaves using multicast Sync messages, the hardware timestamp capture records must be correlated with the correct target slave. 3.1. Sequence ID Range Assignment The 16-bit PTP Sequence ID field provides 65,536 values. When N slaves are served by a single Grandmaster, the Sequence ID space can be divided into N non-overlapping contiguous ranges, each assigned to a specific slave. The Grandmaster transmits Sync messages for each slave using Sequence IDs from that slave's assigned range. The assignment of Sequence ID ranges to slaves MUST be agreed upon by the Grandmaster and all slaves before synchronization begins. The method of assignment (e.g., configuration, management protocol) is outside the scope of this document. 3.2. Grandmaster Timestamp Correlation In Two-Step mode, the Grandmaster retrieves captured timestamps from the hardware and identifies the target slave from the Sequence ID recorded with each timestamp. In One-Step mode, the hardware inserts the timestamp directly into each Sync message; the Sequence ID identifies the target slave for downstream processing. 3.3. Slave Processing Each slave receives all multicast Sync and Follow_Up messages but MUST process only those whose Sequence ID falls within its assigned range. Messages with Sequence IDs outside the assigned range MUST be silently discarded. Li, et al. Expires 5 January 2027 [Page 4] Internet-Draft Multi-Point Telemetry July 2026 4. Security Considerations For the IOAM DEX application, the security considerations of [RFC9326] apply. An attacker that can inject packets with the DEX option could cause telemetry export at all IOAM nodes. IOAM domain ingress filtering SHOULD discard DEX options on packets from untrusted sources. For the PTP application, misconfigured Sequence ID ranges that overlap could cause a slave to process timestamps intended for another slave. Implementations SHOULD validate range assignments for uniqueness. PTP authentication (Annex P of [IEEE-1588]) SHOULD be used in security-sensitive deployments. 5. IANA Considerations This document has no IANA actions. 6. Normative References [IEEE-1588] IEEE, "IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems", IEEE 1588-2019, 2019. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5475] Zseby, T., Molina, M., Duffield, N., Niccolini, S., and F. Raspall, "Sampling and Filtering Techniques for IP Packet Selection", RFC 5475, DOI 10.17487/RFC5475, March 2009, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC9197] Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields for In Situ Operations, Administration, and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197, May 2022, . Li, et al. Expires 5 January 2027 [Page 5] Internet-Draft Multi-Point Telemetry July 2026 [RFC9326] Song, H., Gafni, B., Brockners, F., Bhandari, S., Mizrahi, T., Sivakolundu, R., Li, Z., and T. Zhou, "In Situ Operations, Administration, and Maintenance (IOAM) Direct Exporting", RFC 9326, DOI 10.17487/RFC9326, November 2022, . Authors' Addresses Zhiqiang Li China Mobile Beijing 100053 China Email: lizhiqiangyjy@chinamobile.com Zongpeng Du China Mobile Beijing 100053 China Email: duzongpeng@chinamobile.com Junjie Wang Centec Shanghai 201203 China Email: wangjj@centec.com Wei Cheng Centec Shanghai 201203 China Email: chengw@centec.com Guoying Zhang Centec Shanghai 201203 China Email: zhanggy@centec.com Li, et al. Expires 5 January 2027 [Page 6] Internet-Draft Multi-Point Telemetry July 2026 Xun Sun Inesa Shanghai 200030 China Email: sunxun@inesa.com Chunhao Zhao SAIA Shanghai 200125 China Email: chunhao.zhao@sh-aia.com Li, et al. Expires 5 January 2027 [Page 7]