MPLS Working Group J. Halpern Internet-Draft G. Mirsky Intended status: Standards Track Ericsson Expires: 28 December 2025 26 June 2025 Explicit Congestion Notification Using MPLS Network Actions draft-halmir-mpls-ecn-00 Abstract It has been broadly demonstrated that user experience improvements for time-critical applications have not increased at the same pace as network throughput (i.e., the increased bandwidth does not result in a corresponding increase in the user experience). Optimizing network latency rather than throughput can lead to a significantly improved user experience for time-critical applications. Low Latency, Low Loss, and Scalable Throughput (L4S) technology, introduced in RFC 9330, uses Explicit Congestion Notification (ECN) bits by marking packets suffering potential congestion in the network. L4S operates as a congestion-control mechanism, using markers within the data packets to detect and promptly respond to congestion conditions. This feedback loop enables devices (e.g., endpoints such as client devices and server devices) to adjust data flow in real-time, preventing bottlenecks and ensuring smoother transmission. RFC 5129 describes a mechanism for supporting ECN in the Multiprotocol Label Switching (MPLS) data plane. That mechanism is based on the codepoints that take part in the Traffic Class (TC) field and, thus, prevent the use of TC field for traffic differentiation. This document defines how ECN can be supported in the MPLS data plane using the MPLS Network Actions technology. 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." Halpern & Mirsky Expires 28 December 2025 [Page 1] Internet-Draft ECN Over MNA June 2025 This Internet-Draft will expire on 28 December 2025. Copyright Notice Copyright (c) 2025 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 2. Conventions Used in this Document . . . . . . . . . . . . . . 3 2.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2. Requirements Language . . . . . . . . . . . . . . . . . . 4 3. Realization of Explicit Congestion Notification as an MPLS Network Action . . . . . . . . . . . . . . . . . . . . . 4 3.1. ECN Encapsulation Using In-Stack MPLS Network Actions . . 4 3.2. ECN Encoding Using Post-Stack MPLS Network Actions . . . 5 4. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5.1. ECN as an MPLS Network Action Opcode . . . . . . . . . . 6 5.2. ECN as an Post-Stack Network Action Opcode . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 8.2. Informational References . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction Network throughput (also referred to as bandwidth) has increased exponentially over the last several decades, enabling a variety of new features for end users, including video streaming, online gaming, and mixed reality implementations, as well as more advanced applications such as remote teleoperation and autonomous services. The focus on network throughput, however, underestimates the fact that users are primarily interested in application responsiveness rather than the number of bits they can transfer per second. As a result, user experience improvements for time-critical applications Halpern & Mirsky Expires 28 December 2025 [Page 2] Internet-Draft ECN Over MNA June 2025 have not necessarily increased at the same pace as network throughput (i.e., the increased bandwidth does not result in a corresponding increase in the user experience). Optimizing network latency rather than throughput can lead to a significantly improved user experience for time-critical applications. Low Latency, Low Loss, and Scalable Throughput (L4S) technology, introduced in [RFC9330], uses Explicit Congestion Notification (ECN) ([RFC3168]) bits in IP or TCP by marking packets suffering potential congestion in the network ([RFC9331]). L4S operates as a congestion- control mechanism, using ECN markers within the data packets to detect and promptly respond to congestion conditions. This feedback loop enables devices (e.g., endpoints such as client devices and server devices) to adjust data flow in real-time, preventing bottlenecks and ensuring smoother transmission. [RFC5129] describes a mechanism for supporting ECN in the Multiprotocol Label Switching (MPLS) data plane. That mechanism is based on the codepoints that take part in the Traffic Class (TC) field [RFC3032] and, thus, prevent the use of the TC field for traffic differentiation. This document defines how ECN can be supported in the MPLS data plane using the MPLS Network Actions technology ([I-D.ietf-mpls-mna-fwk]) while preserving the existing MPLS traffic class capability. 2. Conventions Used in this Document 2.1. Acronyms ECN: Explicit Congestion Notification ISD: In-Stack Data L4S: Low Latency, Low Loss, and Scalable Throughput LER: Label Edge Router LSR: Label Switching Router MPLS: Multiprotocol Label Switching MNA: MPLS Network Action NAS: Network Action Sub-stack PSD: Post-Stack Data TC: Traffic Class Halpern & Mirsky Expires 28 December 2025 [Page 3] Internet-Draft ECN Over MNA June 2025 2.2. 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. 3. Realization of Explicit Congestion Notification as an MPLS Network Action MNA, according to [I-D.ietf-mpls-mna-fwk], can support ECN by an MNA Sub-stack using either In-Stack Data (ISD) or Post-Stack Data (PSD) for ancillary data. 3.1. ECN Encapsulation Using In-Stack MPLS Network Actions Figure 1 displays the encoding of ECN using ISD MNA. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opcode ECN | Data1 |ECN|S|U| Data2 | NAL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Format of the ECN MNA Using ISD MNA Where fields are defined as follows: * Opcode ECN is seven-bit field. IANA is requested to assign (TBA1) value Section 5.1. * Data1 is 14-bit field. It MUST be zeroed on transmission and ignored on reception and processing of the Opcode ECN. * ECN is two-bit field. * S is the Bottom of Stack one-bit flag, as defined in [RFC3032] * U is a one-bit Unknown Network Action Handling field as defined in [I-D.ietf-mpls-mna-hdr]. * Data2 is four-bit field. It MUST be zeroed on transmission and ignored on reception and processing of the Opcode ECN. * NAL is three-bit Network Action Length as defined in [I-D.ietf-mpls-mna-hdr]. Halpern & Mirsky Expires 28 December 2025 [Page 4] Internet-Draft ECN Over MNA June 2025 3.2. ECN Encoding Using Post-Stack MPLS Network Actions Figure 2 displays the encoding of ECN using PSD MNA. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |ECN PS-MNA-OP|R|R| PS-NAL |ECN| Post-Stack Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Format of the ECN MNA Using PSD MNA Where the enclosed elements are defined as follows: * ECN PS-MNA-OP is seven-bit field. IANA is requested to assign (TBA2) value (Section 5.2). * R - two Reserved bits as defined in [I-D.ietf-mpls-mna-ps-hdr]. * PS-NAL is seven-bit field as defined in [I-D.ietf-mpls-mna-ps-hdr]. * ECN is two-bit field. * Post-Stack Data is 14-bit field. It MUST be zeroed on transmission and ignored on reception and processing of the ECN PS-MNA-OP. 4. Theory of Operation If an ingress Label Edge Router (LER) that supports this specification is enabled to use ECN MNA receives a packet with the indication that the endpoints of the transport protocol are ECN- capable or packet has experienced congestion, it MUST copy the value of the ECN field in the received IP packet into the ECN field of the ECN MNA using ISD MNA (Figure 1) or of the ECN MNA using PSD MNA (Figure 2). If a transit Label Switching Router (LSR) that supports this specification receives an MPLS packet with MNA ECN and determines that the egress interface for the received packet experiences congestion although its buffer is not full so that the packet can be transmitted (see for the detailed explanation of the incipient congestion [RFC3168]), the LSR MUST set the ECN field to the Congestion Experienced (0b11) value. If an egress LER that supports this specification, receives an MPLS packet with ECN MNA, it MUST combine the value of the ECN field with the value in the ECN field of the IP header of the encapsulated packet. Halpern & Mirsky Expires 28 December 2025 [Page 5] Internet-Draft ECN Over MNA June 2025 In some scenarios, the Readable Label Depth of the constructed path through the MPLS domain may require the placement of more than one ECN MNA Network Action Sub-stacks (NASes). If that is the case, then the Label Switching Router that exposes the NAS with ECN MNA MUST copy the value of the ECN field in that NAS into the ECN field in the next NAS that includes ECN MNA. 5. IANA Considerations 5.1. ECN as an MPLS Network Action Opcode IANA is requested to assign an ECN codepoint (TBA1) from its Network Action Opcodes registry (creation requested in [I-D.ietf-mpls-mna-hdr]) as specified in Table 1. +========+======================================+===============+ | Opcode | Description | Reference | +========+======================================+===============+ | TBA1 | ECN as MPLS Network Action Indicator | This document | +--------+--------------------------------------+---------------+ Table 1: ECN as MPLS Network Action Opcode 5.2. ECN as an Post-Stack Network Action Opcode IANA is requested to assign an ECN codepoint (TBA1) from its Post- Stack Network Action Opcodes registry (creation requested in [I-D.ietf-mpls-mna-ps-hdr]) as specified in Table 2. +========+=========================================+===============+ | Opcode | Description | Reference | +========+=========================================+===============+ | TBA2 | ECN as Post-Stack Network Action Opcode | This document | +--------+-----------------------------------------+---------------+ Table 2: ECN as MPLS Network Action Opcode 6. Security Considerations Security considerations discussed in [RFC9197], [RFC9326], and [I-D.ietf-mpls-mna-fwk] apply to this document. 7. Acknowledgments TBA 8. References Halpern & Mirsky Expires 28 December 2025 [Page 6] Internet-Draft ECN Over MNA June 2025 8.1. Normative References [I-D.ietf-mpls-mna-fwk] Andersson, L., Bryant, S., Bocci, M., and T. Li, "MPLS Network Actions (MNA) Framework", Work in Progress, Internet-Draft, draft-ietf-mpls-mna-fwk-15, 27 December 2024, . [I-D.ietf-mpls-mna-hdr] Rajamanickam, J., Gandhi, R., Zigler, R., Song, H., and K. Kompella, "MPLS Network Action (MNA) Sub-Stack Solution", Work in Progress, Internet-Draft, draft-ietf-mpls-mna-hdr- 12, 3 March 2025, . [I-D.ietf-mpls-mna-ps-hdr] Rajamanickam, J., Gandhi, R., Zigler, R., Li, T., and J. Dong, "Post-Stack MPLS Network Action (MNA) Solution", Work in Progress, Internet-Draft, draft-ietf-mpls-mna-ps- hdr-01, 30 May 2025, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001, . [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition of Explicit Congestion Notification (ECN) to IP", RFC 3168, DOI 10.17487/RFC3168, September 2001, . [RFC5129] Davie, B., Briscoe, B., and J. Tay, "Explicit Congestion Marking in MPLS", RFC 5129, DOI 10.17487/RFC5129, January 2008, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Halpern & Mirsky Expires 28 December 2025 [Page 7] Internet-Draft ECN Over MNA June 2025 [RFC9197] Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi, Ed., "Data Fields for In Situ Operations, Administration, and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197, May 2022, . [RFC9326] Song, H., Gafni, B., Brockners, F., Bhandari, S., and T. Mizrahi, "In Situ Operations, Administration, and Maintenance (IOAM) Direct Exporting", RFC 9326, DOI 10.17487/RFC9326, November 2022, . 8.2. Informational References [RFC9330] Briscoe, B., Ed., De Schepper, K., Bagnulo, M., and G. White, "Low Latency, Low Loss, and Scalable Throughput (L4S) Internet Service: Architecture", RFC 9330, DOI 10.17487/RFC9330, January 2023, . [RFC9331] De Schepper, K. and B. Briscoe, Ed., "The Explicit Congestion Notification (ECN) Protocol for Low Latency, Low Loss, and Scalable Throughput (L4S)", RFC 9331, DOI 10.17487/RFC9331, January 2023, . Authors' Addresses Joel Halpern Ericsson Email: jmh@joelhalpern.com Greg Mirsky Ericsson Email: gregimirsky@gmail.com Halpern & Mirsky Expires 28 December 2025 [Page 8]