]>

david@none.org

LabN Consulting, L.L.C.

lberger@labn.net

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

Introduction The Dynamic Link Exchange Protocol (DLEP) is defined in . This protocol provides the exchange of link related control information between DLEP peers. DLEP peers are comprised 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. There are various flow control techniques theoretically possible with DLEP. This document defines a DLEP extension which provides an Ethernet-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 a DiffServ-based version of credit window flow control. This document uses the traffic classification and credit window control mechanisms defined in and to provide credit window based flow control based on DLEP destinations and Ethernet VLANs and Priority Code Points. Ethernet Priority Code Point support is defined as part of the IEEE 802.1Q tag format and includes a 3 bit "PCP" field. The tag format also includes a 12 bit VLAN identifier (VID) field. The defined mechanism allows for credit windows to be shared across traffic sent to multiple DLEP destinations, VLANs, and PCPs, or used exclusively for traffic sent to a particular destination and/or VLAN and/or PCP. The extension also supports the "wildcard" matching of any PCP or VID. The extension defined in this document is referred to as "IEEE 802.1Q Aware Credit Window" or, more simply, the "Ethernet Credit" extension. The reader should be familiar with both the traffic classification and credit window control mechanisms defined in and . This document defines a new DLEP Extension Type Value in which is used to indicate support for the extension.

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 composed of the mechanisms and processing defined in and . To indicate that the IEEE 802.1Q Aware Credit Window Extension is to be used, an implementation MUST include the IEEE 802.1Q Aware Credit Window Type Value in the Extensions Supported Data Item. The Extensions Supported Data Item is sent and processed according to . Any implementation that indicates use of the IEEE 802.1Q Aware Credit Window Extension MUST support all Messages, Data Items, the Ethernet Traffic Classification Sub-Data Item, and all related processing defined in and . The IEEE 802.1Q Aware Credit Window Extension Type Value is TBA1, see .

Management Considerations This section provides several network management guidelines to implementations supporting the IEEE 802.1Q Aware Credit Window Extension. The use of the extension defined in this document SHOULD be configurable on both modems and routers. Modems SHOULD support the configuration of PCP to credit window (queue) mapping. Modems MAY support the configuration of PCP to credit window (queue) mapping on a per VLAN basis. Note that VID value of zero (0) is used by to indicate that VID is ignored and any VID value is used in traffic classification. When VLANs are supported by a modem without support from PCPs, the modem SHOULD support the configuration of VLAN to credit window (queue) mapping. 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, perhaps, even limits in supported credit window combinations, e.g., if per destination queues can even be supported at all. When modem-provided credit window information 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, the mismatch of capabilities SHOULD be reported to the user via normal network management mechanisms, e.g., user interface 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 control and flow mechanisms defined in and . The defined extension exposes vulnerabilities similar to existing DLEP messages, e.g., an injected message resizes 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.

IANA Considerations This document requests one assignment by IANA. All assignments are to registries defined by .

Extension Type Value This document requests 1 new assignment to the DLEP Extensions Registry named "Extension Type Values" in the range with the "Specification Required" policy. The requested value is as follows: Requested Extension Type Value

Code	Description
TBA1	IEEE 802.1Q Aware Credit Window

References Normative References IEEE This standard specifies how the Media Access Control (MAC) Service is supported by Bridged Networks, the principles of operation of those networks, and the operation of MAC Bridges and VLAN Bridges, including management, protocols, and algorithms 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 MIT Lincoln Laboratory LabN Consulting, L.L.C. This document defines new Dynamic Link Exchange Protocol (DLEP) Data Items that are used to support credit-based flow control. Credit window control is used to regulate when data may be sent to an associated virtual or physical queue. The Data Items are defined in an extensible and reusable fashion. Their use will be mandated in other documents defining specific DLEP extensions. MIT Lincoln Laboratory MIT Lincoln Laboratory LabN Consulting, L.L.C. This document defines a new Dynamic Link Exchange Protocol (DLEP) Data Item that is used to support traffic classification. Traffic classification information is used to identify traffic flows based on frame/packet content such as destination address. The Data Item is defined in an extensible and reusable fashion. Its use will be mandated in other documents defining specific DLEP extensions. This document also introduces DLEP Sub-Data Items, and Sub-Data Items are defined to support DiffServ and Ethernet traffic classification. Informative References MIT Lincoln Laboratory MIT Lincoln Laboratory LabN Consulting, L.L.C. 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.

Acknowledgments The document was motivated by discussions in the MANET working group. Many useful comments were received from contributors to the MANET working group, notably Ronald in't Velt. We had the honor of working too briefly with David Wiggins 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 morn his passing on November 23, 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.