DLEP DiffServ Aware Credit Window Extension

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Table of Contents

1. Introduction

The Dynamic Link Exchange Protocol (DLEP) is defined in [RFC8175]. This 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. There are various flow control techniques theoretically possible with DLEP. This document defines a DLEP extension which 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 [I-D.ietf-manet-dlep-ether-credit-extension] for an Ethernet-based version of credit window flow control. As specified in Section 2.3.1 of [I-D.ietf-manet-dlep-traffic-classification], when both DiffServ and Ethernet traffic classification are specified for a flow, the Ethertype information takes precedence.¶

This document uses the traffic classification and credit window control mechanisms defined in [I-D.ietf-manet-dlep-traffic-classification] and [I-D.ietf-manet-dlep-credit-flow-control] to provide credit window based flow control based on DLEP destinations and DiffServ [RFC2475] DSCPs (differentiated services codepoints). 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 "DiffServ Aware Credit Window" or, more simply, the "DA Credit" extension. The reader should be familiar with both the traffic classification and credit window control mechanisms defined in [I-D.ietf-manet-dlep-traffic-classification] and [I-D.ietf-manet-dlep-credit-flow-control].¶

This document defines a new DLEP Extension Type Value in Section 2 which is used to indicate support for the extension.¶

2. Extension Usage and Identification

The extension defined in this document is composed of the mechanisms and processing defined in [I-D.ietf-manet-dlep-traffic-classification] and [I-D.ietf-manet-dlep-credit-flow-control]. To indicate that the DiffServ Aware Credit Window Extension is to be used, an implementation MUST include the DiffServ Aware Credit Window Type Value in the Extensions Supported Data Item (see Section 13.6 of [RFC8175]). The Extensions Supported Data Item is sent and processed according to [RFC8175]. Any implementation that indicates use of the DiffServ Aware Credit Window Extension MUST support all Messages, Data Items, the DiffServ Traffic Classification Sub-Data Item, and all related processing defined in [I-D.ietf-manet-dlep-traffic-classification] and [I-D.ietf-manet-dlep-credit-flow-control].¶

The DiffServ Aware Credit Window Extension Type Value is TBA1, see Section 5.¶

3. Management Considerations

This section provides several network management guidelines to implementations supporting the DiffServ Aware Credit Window Extension.¶

If this extension is supported, that support MUST be declare 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 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.¶

Modems SHOULD support the configuration of DSCP 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 limits on supported credit window combinations. Per destination queues might not 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 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.¶

4. Security Considerations

This document defines a DLEP extension that uses DLEP mechanisms and the credit window control and flow mechanisms defined in [I-D.ietf-manet-dlep-traffic-classification] and [I-D.ietf-manet-dlep-credit-flow-control]. The defined extension is exposed to vulnerabilities similar to existing DLEP messages and discussed in the Security Considerations section of [RFC8175] such as an injected message resizing a credit window to a value that results in a denial of service. Wildcards for matching Priority Code point (PCP) and VLAN ID (VID) fields (see [I-D.ietf-manet-dlep-ether-credit-extension]) are provided which may be convenient to match 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. The security mechanisms documented in [RFC8175] can be applied equally to the mechanism defined in this document.¶

5. IANA Considerations

IANA is requested to assign one code point in the "Extension Type Values" registry in the "Dynamic Link Exchange Protocol (DLEP) Parameters" registry group as follows:¶

Authors' Addresses