RFC 9895

Dynamic Link Exchange Protocol (DLEP) IEEE 802.1Q Aware Credit Window Extension

📅 published January 2026, from ietf

🎀 RFC 9895: Dynamic Link Exchange Protocol (DLEP) IEEE 802.1Q Aware Credit Window Extension ✨

Okay bestie, this is the RFC that teaches DLEP to do flow control with Ethernet vibes 🦋💅. Let's get into it!

Here's the title block tea ☕: the authors are D. Wiggins, L. Berger (LabN Consulting, L.L.C.), and D. Eastlake 3rd, Ed. (listed as Independent). It's a Standards Track document, the ISSN is 2070-1721, and it's dated January 2026 📅. It doesn't obsolete anything, and it doesn't update anything either. It's a brand new extension, so it's giving fresh start 🌸.

Also, the RFC number is 9895 and the Internet Engineering Task Force (IETF) is the org behind it 🌈.

Abstract

This doc defines an extension to the Dynamic Link Exchange Protocol (DLEP) that enables an Ethernet IEEE 802.1Q aware credit window scheme for destination-specific and shared flow control. Ethernet credit windows, totally iconic 💖.

Status of This Memo

This is an Internet Standards Track document. It's official, it's serious, and it's been fully vetted 🔥.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841 🧚.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9895 💜.

Copyright Notice

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 🙈.

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's the protocol that handles the exchange of link-related control info between DLEP peers. The peers are a modem and a router, and that's the whole cast 💅. DLEP comes with a base set of mechanisms plus room for extensions, and this document is one of those extensions 🎀.

Here's the thing: DLEP doesn't define any flow control mechanisms at all 😭. In theory you could build flow control on DLEP, but this doc specifies an extension that adds an Ethernet-based flow control mechanism for traffic going from a router to a modem 🦋. It works with one or more logical "credit windows," and each one is usually tied to a virtual or physical queue 🧚. The router uses the traffic flow classification info the modem gives it to pick the right credit window for each flow ✨. Credit windows can be shared across several flows, or used per-flow, which is so customizable 👑. If you want the Diffserv version of credit window flow control, check out [RFC9894] 💖. And as Section 2.3.1 of [RFC9892] says, when both Diffserv and Ethernet classification apply to a flow, Ethernet-based classification takes precedence 🙈.

This document pulls in the traffic classification and credit window flow control mechanisms from [RFC9892] and [RFC9893] to get credit-window-based flow control working with DLEP destinations, Ethernet Virtual Local Area Networks (VLANs), and Priority Code Points (PCPs) 💅. Ethernet PCP support comes from the IEEE 802.1Q tag format [IEEE8021Q], which has a 3-bit "PCP" field 🌈. The same tag format also has a 12-bit "VLAN Identifier (VID)" field 🍓.

So the defined mechanism lets credit windows be shared across traffic going to multiple DLEP destinations, VLANs, and PCPs, or be dedicated to traffic for one specific destination, VLAN, and/or PCP 🦋. And this extension also supports "wildcard" matching for any PCP or VID, which is giving flexibility 💜.

The extension in this doc is called the "IEEE 802.1Q Aware Credit Window," or just the "Ethernet Credit" extension ⭐. Readers should already know both the traffic classification and credit window flow control mechanisms from [RFC9892] and [RFC9893] 🫶.

Last thing: this document defines a new DLEP Extension Type value that signals support for the extension. See Section 2 🎀.

1.1. Key Words 🔑

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 🧚

The extension here is built on the mechanisms and processing from [RFC9892] and [RFC9893] ✨. To say that the IEEE 802.1Q Aware Credit Window Extension is in use, an implementation MUST include the IEEE 802.1Q 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 says it's using the IEEE 802.1Q Aware Credit Window Extension MUST support all message types, Data Items, the Ethernet Traffic Classification Sub-Data Item, and all related processing defined in [RFC9892] and [RFC9893] 👑.

The IEEE 802.1Q Aware Credit Window Extension Type value is 5 🍓. See Section 5 🌈.

3. Management Considerations 🎀

This section gives some network management guidelines for implementations that support the IEEE 802.1Q 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]), which can be configured on both modems and routers ✨. Diffserv Aware Credit Window Extension Data Items MUST NOT be emitted by a DLEP participant unless that support was specified in the initialization message received from its peer 🙈. Using the extension defined in this document SHOULD be configurable on both modems and routers 💅.

Modems SHOULD support configuring a mapping from a PCP to a credit window (queue) 🧚.

Modems MAY support configuring a mapping from a PCP to a credit window (queue) on a per-VLAN basis 💖. VID value zero (0x0000) is used by [RFC9892] to indicate that the VID is ignored 🫶. VID 0xFFFF is reserved 😭. Any other VID value from 0x0001 through 0xFFFE can be used in traffic classification 🌸.

When a modem supports VLANs without support from PCPs, the modem SHOULD support configuring a mapping from a VLAN to a credit window (queue) 🦋.

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

Routers may impose limits on how many queues they can support and on the allowed credit window configurations 🍓. In some cases, per-destination queues may not be supported 🌈. If the credit window info from the modem goes beyond the router's capabilities, the router SHOULD use a subset of the advertised credit windows 👑. Alternatively, the 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 standard network management mechanisms, like user interface notifications or error logging 🎀.

No matter how it's implemented, if credit windows are in use, the router MUST NOT send traffic to the modem unless sufficient credits are available 🚫✨.

Quick reminder: the router is never allowed to send traffic without enough credits. That's the whole vibe of flow control 💀.

4. Security Considerations 🔐

This document defines a DLEP extension that uses DLEP mechanisms and the credit window flow control mechanisms from [RFC9892] and [RFC9893] 💅. Check the Security Considerations sections of those documents too 🫶.

The extension is exposed to vulnerabilities similar to existing DLEP messages, which are discussed in the Security Considerations section of [RFC8175] 😭. One 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 PCP and VID fields are provided 🌈. Wildcards may be 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 has been set up 🙈. So it is RECOMMENDED that wildcards not be used unless they're clearly 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                     |
              +======+=================================+
              | 5    | IEEE 802.1Q Aware Credit Window |
              +------+---------------------------------+

                    Table 1: Extension Type Value

6. References 📚

6.1. Normative References

[IEEE8021Q]
           IEEE, "IEEE Standard for Local and Metropolitan Area
           Networks--Bridges and Bridged Networks",
           DOI 10.1109/IEEESTD.2022.10004498, IEEE Std 802.1Q-2022,
           December 2022,
           <https://ieeexplore.ieee.org/document/10004498>.

[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

[RFC9894]  Cheng, B., Wiggins, D., Berger, L., and D. Eastlake 3rd,
           Ed., "Dynamic Link Exchange Protocol (DLEP) Diffserv Aware
           Credit Window Extension", RFC 9894, DOI 10.17487/RFC9894,
           January 2026, <https://www.rfc-editor.org/info/rfc9894>.

Acknowledgments 🎀

okay so this section is basically a big thank-you note, and it's kinda emotional ngl 🥹 This document was motivated by discussions in the MANET Working Group, and a bunch of useful comments came in from contributors to that group, especially Ronald in 't Velt. Iconic of them 🫶

We were honored to work with David Wiggins on this and related DLEP work, even though it was only for a little while 🥺 His contributions to the IETF, and the publication of the first and definitive open-source DLEP implementation, were critical to DLEP being accepted. We are so sad that he passed away on November 26, 2023 💜 We want to recognize his guidance, leadership, and professional excellence. We were lucky to learn from his leadership and his friendship. He shall be missed 🕊️

Authors' Addresses 💌

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

That's the whole RFC, bestie! 🌈✨ Thanks for reading along. 💅

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