MIT Lincoln Laboratory

Massachusetts Institute of Technology 244 Wood Street Lexington MA 02421-6426 United States of America bcheng@ll.mit.edu

LabN Consulting, L.L.C.

lberger@labn.net

Independent

2386 Panoramic Circle Apopka FL 32703 United States of America +1-508-333-2270 d3e3e3@gmail.com

RTG manet This document defines an extension to the Dynamic Link Exchange Protocol (DLEP) that enables a Diffserv aware credit window scheme for destination-specific and shared flow control.

Status of This Memo This is an Internet Standards Track document. 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 .

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 () 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

• .  Introduction
  • .  Key Words
• .  Extension Usage and Identification
• .  Management Considerations
• .  Security Considerations
• .  IANA Considerations
• .  References
  • .  Normative References
  • .  Informative References
• Acknowledgments
• Authors' Addresses

Introduction The Dynamic Link Exchange Protocol (DLEP) is defined in . The protocol provides the exchange of link-related control information between DLEP peers. DLEP peers consist of a modem and a router. DLEP defines a base set of mechanisms as well as support for possible extensions. This document defines one such extension. The DLEP specification does not include any flow control capability. Various flow control techniques are theoretically possible with DLEP. This document defines a DLEP extension that provides a Diffserv-based flow control mechanism for traffic sent from a router to a modem. Flow control is provided using one or more logical "credit windows", each of which will typically be supported by an associated virtual or physical queue. A router will use traffic flow classification information provided by the modem to identify which traffic is associated with each credit window. Credit windows may be shared or dedicated on a per-flow basis. See for an Ethernet-based version of credit window flow control. As specified in , when both Diffserv and Ethernet traffic classification are specified for a flow, the Ethernet information takes precedence. This document uses the traffic classification and credit window flow control mechanisms defined in and to provide credit-window-based flow control based on DLEP destinations and Differentiated Services Code Points (DSCPs) . The defined mechanism allows for credit windows to be shared across traffic sent to multiple DLEP destinations and DSCPs, or used exclusively for traffic sent to a particular destination and/or DSCP. The extension also supports the "wildcard" matching of any DSCP. The extension defined in this document is referred to as the "Diffserv Aware Credit Window" or, more simply, the "DA Credit" extension. The reader should be familiar with both the traffic classification and credit window flow control mechanisms defined in and . This document defines a new DLEP Extension Type value that is used to indicate support for the extension. See .

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 when, and only when, they appear in all capitals, as shown here.

Extension Usage and Identification The extension defined in this document is built on the mechanisms and processing defined in and . To indicate that the Diffserv Aware Credit Window Extension is to be used, an implementation MUST include the Diffserv Aware Credit Window Extension Type value in the Extensions Supported Data Item (see ). The Extensions Supported Data Item is sent and processed according to . Any implementation that indicates the 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 and . The Diffserv Aware Credit Window Extension Type value is 6. See .

Management Considerations This section provides several network management guidelines for implementations supporting the Diffserv Aware Credit Window Extension. If this extension is supported, that support MUST be declared using the Extensions Supported Data Item (see ). Diffserv Aware Credit Window Extension Data Items MUST NOT be emitted by a DLEP participant unless such support was specified in the initialization message received from its peer. The use of the extension defined in this document SHOULD be configurable on both modems and routers. That configuration can be implemented using 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 the configuration of mapping a DSCP to a credit window (queue). Modems MAY support the configuration of the number of credit windows (queues) to advertise to a router. Routers may have limits on the number of queues that they can support and limits on supported credit window combinations. Per-destination queues might not be supported at all. When credit window information provided by a modem exceeds the capabilities of a router, 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. In either case, any mismatch in capabilities SHOULD be reported to the user via normal network management mechanisms, such as 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.

Security Considerations This document defines a DLEP extension that uses DLEP mechanisms and the credit window flow control mechanisms defined in and . See also the Security Considerations sections of those documents. The defined extension is exposed to vulnerabilities similar to existing DLEP messages and discussed in the Security Considerations section of , such as an injected message resizing a credit window to a value that results in a denial of service. The security mechanisms documented in can be applied equally to the mechanism defined in this document. Wildcards for matching Priority Code Point (PCP) and VLAN Identifier (VID) fields (see ) are provided. Note that wildcards may be convenient for matching a number of packet flows but could inadvertently match unexpected flows or new flows that appear after the wildcard matching has been set up. It is therefore RECOMMENDED that wildcards not be used unless needed.

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: Extension Type Value

Code	Description
6	Diffserv Aware Credit Window

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. When routing devices rely on modems to effect communications over wireless links, they need timely and accurate knowledge of the characteristics of the link (speed, state, etc.) in order to make routing decisions. In mobile or other environments where these characteristics change frequently, manual configurations or the inference of state through routing or transport protocols does not allow the router to make the best decisions. This document introduces a new protocol called the Dynamic Link Exchange Protocol (DLEP), which provides a bidirectional, event-driven communication channel between the router and the modem to facilitate communication of changing link characteristics. MIT Lincoln Laboratory LabN Consulting, L.L.C. LabN Consulting, L.L.C. MIT Lincoln Laboratory LabN Consulting, L.L.C. LabN Consulting, L.L.C. Informative References This document defines an architecture for implementing scalable service differentiation in the Internet. This memo provides information for the Internet community. LabN Consulting, L.L.C. Independent

Acknowledgments Many useful comments were received from contributors to the MANET Working Group, notably . We had the honor of working too briefly with on this and related DLEP work. His contribution to the IETF and publication of the first and definitive open-source DLEP implementation have been critical to the acceptance of DLEP. 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 MIT Lincoln Laboratory

Massachusetts Institute of Technology 244 Wood Street Lexington MA 02421-6426 United States of America bcheng@ll.mit.edu

LabN Consulting, L.L.C.

lberger@labn.net

Independent

2386 Panoramic Circle Apopka FL 32703 United States of America +1-508-333-2270 d3e3e3@gmail.com