RFC 9894

Dynamic Link Exchange Protocol (DLEP) Diffserv Aware Credit Window Extension

📅 published January 2026, from ietf

RFC 9894: Dynamic Link Exchange Protocol (DLEP) Diffserv Aware Credit Window Extension ✨

Bestie, here's the deal 🎀 This is RFC 9894 from the IETF. It's a Standards Track doc (ISSN 2070-1721), dated January 2026. The authors are B. Cheng (MIT Lincoln Laboratory), D. Wiggins, L. Berger (LabN Consulting, L.L.C.), and D. Eastlake 3rd, Ed. (Independent). The title block doesn't list anything it obsoletes or updates 🦋

Abstract 🌸

Okay so this doc adds an extension to the Dynamic Link Exchange Protocol (DLEP) 💖 It gives you a Diffserv aware credit window scheme for flow control that works per destination or shared across destinations ✨

Status of This Memo 📜

This is an Internet Standards Track document 🎀

This is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It went through public review and got approved for publication by the Internet Engineering Steering Group (IESG). For more on Internet Standards, check Section 2 of RFC 7841 🫶

Info about the current status of this doc, any errata, and how to send feedback lives at https://www.rfc-editor.org/info/rfc9894 🔥

Copyright Notice ©️

This doc is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) as they stand on the publication date. Read those carefully, because they spell out your rights and restrictions for this doc 👀 Code Components pulled out of this doc have to include Revised BSD License text, as described in Section 4.e of the Trust Legal Provisions, and they come with no warranty, as the Revised BSD License describes 🌈

Table of Contents 🧚

1.  Introduction
  1.1.  Key Words
2.  Extension Usage and Identification
3.  Management Considerations
4.  Security Considerations
5.  IANA Considerations
6.  References
  6.1.  Normative References
  6.2.  Informative References
Acknowledgments
Authors' Addresses

1. Introduction 🦋

Okay so DLEP is defined in [RFC8175] 💅 It handles the exchange of link-related control information between DLEP peers. The peers are a modem and a router. DLEP comes with a base set of mechanisms plus room for extensions, and this doc is one of those extensions ✨

Here's the thing: DLEP has no flow control capability at all 😭 Flow control is theoretically possible, but there's nothing built in. So this doc defines a DLEP extension that gives you a Diffserv-based flow control mechanism for traffic going from a router to a modem 🍓 Flow control uses one or more logical "credit windows," and each one usually gets backed by a virtual or physical queue. The router uses traffic flow classification info from the modem to figure out which traffic belongs to which credit window. Credit windows can be shared, or dedicated on a per-flow basis 👑 For an Ethernet-based version of credit window flow control, see [RFC9895]. As Section 2.3.1 of [RFC9892] explains, if both Diffserv and Ethernet traffic classification are specified for a flow, the Ethernet info wins 💀

This doc uses the traffic classification and credit window flow control mechanisms from [RFC9892] and [RFC9893] to get credit-window-based flow control working by DLEP destinations and Differentiated Services Code Points (DSCPs) [RFC2475] 🌸 The mechanism lets credit windows be shared across traffic sent to multiple DLEP destinations and DSCPs, or used exclusively for traffic going to one particular destination and/or DSCP. The extension also supports "wildcard" matching of any DSCP 🫶

We call the extension in this doc the "Diffserv Aware Credit Window," or more simply, the "DA Credit" extension 🎀 You should be familiar with both the traffic classification and credit window flow control mechanisms from [RFC9892] and [RFC9893] before you dive in 🧚

This doc defines a new DLEP Extension Type value that signals support for the extension. See Section 2 🦋

1.1. Key Words 👑

Pay attention here, this part's important 💅 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. Extension Usage and Identification 🌈

This extension is built on the mechanisms and processing defined in [RFC9892] and [RFC9893] 💖 To say that the Diffserv Aware Credit Window Extension is in use, an implementation MUST include the Diffserv Aware Credit Window Extension Type value in the Extensions Supported Data Item (see Section 13.6 of [RFC8175]). The Extensions Supported Data Item gets sent and processed according to [RFC8175] 🎀 Any implementation that indicates use of the Diffserv Aware Credit Window Extension MUST support all message types, Data Items, the Diffserv Traffic Classification Sub-Data Item, and all related processing defined in [RFC9892] and [RFC9893] 🔥

The Diffserv Aware Credit Window Extension Type value is 6. See Section 5 🍓

3. Management Considerations 🧚

This section gives several network management guidelines for implementations that support the Diffserv Aware Credit Window Extension 🦋

If this extension is supported, that support MUST be declared using the Extensions Supported Data Item (see Section 13.6 of [RFC8175]). Diffserv Aware Credit Window Extension Data Items MUST NOT be emitted by a DLEP participant unless that support was specified in the initialization message it received from its peer 🙈 The use of the extension in this doc SHOULD be configurable on both modems and routers. That configuration can be done with a proprietary Command-Line Interface or by implementing a YANG module. The definition of the YANG module is out of scope for this document 💜

Modems SHOULD support configuring the mapping of a DSCP to a credit window (queue) ✨

Modems MAY support configuring the number of credit windows (queues) to advertise to a router 🌸

Routers may have limits on the number of queues they can support and limits on supported credit window combinations. Per-destination queues might not be supported at all 😭 When the credit window info from a modem goes beyond what a router can handle, the router SHOULD use a subset of the provided credit windows. Alternatively, a router MAY reset the session and indicate that the extension is not supported. Either way, any capability mismatch SHOULD be reported to the user through normal network management mechanisms, like user interface messages or error logging 🫶

In all cases, if credit windows are in use, traffic for which credits are not available MUST NOT be sent to the modem by the router 🚫💅

4. Security Considerations 🔒

This doc defines a DLEP extension that uses DLEP mechanisms and the credit window flow control mechanisms from [RFC9892] and [RFC9893]. Also check the Security Considerations sections of those docs 👀

The extension is exposed to vulnerabilities that are similar to existing DLEP messages, as discussed in the Security Considerations section of [RFC8175]. For example, an injected message could resize a credit window to a value that causes a denial of service 😱 The security mechanisms documented in [RFC8175] can be applied equally to the mechanism defined in this document 🛡️

Wildcards for matching Priority Code Point (PCP) and VLAN Identifier (VID) fields (see [RFC9895]) are provided. Heads up, wildcards are convenient for matching a bunch of packet flows, but they could accidentally match unexpected flows or new flows that show up after the wildcard matching is set up 💀 It is therefore RECOMMENDED that wildcards not be used unless needed 🙈

5. IANA Considerations 🌈

IANA has assigned the following code point in the "Extension Type Values" registry in the "Dynamic Link Exchange Protocol (DLEP) Parameters" registry group 💖

              +======+==============================+
              | Code | Description                  |
              +======+==============================+
              | 6    | Diffserv Aware Credit Window |
              +------+------------------------------+

                   Table 1: Extension Type Value

6. References 📚

6.1. 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,
           <https://www.rfc-editor.org/info/rfc2119>.

[RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
           2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
           May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC8175]  Ratliff, S., Jury, S., Satterwhite, D., Taylor, R., and B.
           Berry, "Dynamic Link Exchange Protocol (DLEP)", RFC 8175,
           DOI 10.17487/RFC8175, June 2017,
           <https://www.rfc-editor.org/info/rfc8175>.

[RFC9892]  Cheng, B., Wiggins, D., Berger, L., and D. Fedyk, Ed.,
           "Dynamic Link Exchange Protocol (DLEP) Traffic
           Classification Data Item", RFC 9892, DOI 10.17487/RFC9892,
           January 2026, <https://www.rfc-editor.org/info/rfc9892>.

[RFC9893]  Cheng, B., Wiggins, D., Ratliff, S., Berger, L., and E.
           Kinzie, Ed., "Dynamic Link Exchange Protocol (DLEP)
           Credit-Based Flow Control Messages and Data Items",
           RFC 9893, DOI 10.17487/RFC9893, January 2026,
           <https://www.rfc-editor.org/info/rfc9893>.

6.2. Informative References 💜

[RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
           and W. Weiss, "An Architecture for Differentiated
           Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
           <https://www.rfc-editor.org/info/rfc2475>.

[RFC9895]  Wiggins, D., Berger, L., and D. Eastlake 3rd, Ed.,
           "Dynamic Link Exchange Protocol (DLEP) IEEE 802.1Q Aware
           Credit Window Extension", RFC 9895, DOI 10.17487/RFC9895,
           January 2026, <https://www.rfc-editor.org/info/rfc9895>.

Acknowledgments 🫶

Many useful comments came in from contributors to the MANET Working Group, especially Ronald in 't Velt 🌸

We had the honor of working too briefly with David Wiggins on this and related DLEP work. His contributions to the IETF, and his publication of the first and definitive open-source DLEP implementation, were critical to DLEP's acceptance. We mourn his passing on November 26, 2023. We wish to recognize his guidance, leadership, and professional excellence. We were fortunate to benefit from his leadership and friendship. He shall be missed 🥹🌈

Authors' Addresses 💌

okay bestie, here are the girlies who wrote this, with their contact info so you can slide into their DMs 🫶

Bow-Nan Cheng
MIT Lincoln Laboratory
Massachusetts Institute of Technology
244 Wood Street
Lexington, MA 02421-6426
United States of America
Email: bcheng@ll.mit.edu


David Wiggins


Lou Berger
LabN Consulting, L.L.C.
Email: lberger@labn.net


Donald E. Eastlake 3rd (editor)
Independent
2386 Panoramic Circle
Apopka, FL 32703
United States of America
Phone: +1-508-333-2270
Email: d3e3e3@gmail.com

📦 where this page comes from

ietf: rfc9894 2026-01
💖 girlified by claude-haiku-5-5 on 2026-10-19: a language model's rewrite of the original, under its terms