rfc9894v1.txt   rfc9894.txt 
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D. Eastlake 3rd, Ed. D. Eastlake 3rd, Ed.
Independent Independent
November 2025 November 2025
Dynamic Link Exchange Protocol (DLEP) Diffserv Aware Credit Window Dynamic Link Exchange Protocol (DLEP) Diffserv Aware Credit Window
Extension Extension
Abstract Abstract
This document defines an extension to the Dynamic Link Exchange This document defines an extension to the Dynamic Link Exchange
Protocol (DLEP) that enables a Diffserv aware credit-window scheme Protocol (DLEP) that enables a Diffserv aware credit window scheme
for destination-specific and shared flow control. for destination-specific and shared flow control.
Status of This Memo Status of This Memo
This is an Internet Standards Track document. This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has (IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on Internet Engineering Steering Group (IESG). Further information on
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Flow control is provided using one or more logical "Credit Windows", Flow control is provided using one or more logical "Credit Windows",
each of which will typically be supported by an associated virtual or each of which will typically be supported by an associated virtual or
physical queue. A router will use traffic flow classification physical queue. A router will use traffic flow classification
information provided by the modem to identify which traffic is information provided by the modem to identify which traffic is
associated with each credit window. Credit windows may be shared or associated with each credit window. Credit windows may be shared or
dedicated on a per-flow basis. See [RFC9895] for an Ethernet-based dedicated on a per-flow basis. See [RFC9895] for an Ethernet-based
version of credit window flow control. As specified in Section 2.3.1 version of credit window flow control. As specified in Section 2.3.1
of [RFC9892], when both Diffserv and Ethernet traffic classification of [RFC9892], when both Diffserv and Ethernet traffic classification
are specified for a flow, the Ethernet information takes precedence. are specified for a flow, the Ethernet information takes precedence.
This document uses the traffic classification and credit window This document uses the traffic classification and credit window flow
control mechanisms defined in [RFC9892] and [RFC9893] to provide control mechanisms defined in [RFC9892] and [RFC9893] to provide
credit-window-based flow control based on DLEP destinations and credit-window-based flow control based on DLEP destinations and
Differentiated Services Code Points (DSCPs) [RFC2475]. The defined Differentiated Services Code Points (DSCPs) [RFC2475]. The defined
mechanism allows for credit windows to be shared across traffic sent mechanism allows for credit windows to be shared across traffic sent
to multiple DLEP destinations and DSCPs, or used exclusively for to multiple DLEP destinations and DSCPs, or used exclusively for
traffic sent to a particular destination and/or DSCP. The extension traffic sent to a particular destination and/or DSCP. The extension
also supports the "wildcard" matching of any DSCP. also supports the "wildcard" matching of any DSCP.
The extension defined in this document is referred to as the The extension defined in this document is referred to as the
"Diffserv Aware Credit Window" or, more simply, the "DA Credit" "Diffserv Aware Credit Window" or, more simply, the "DA Credit"
extension. The reader should be familiar with both the traffic extension. The reader should be familiar with both the traffic
classification and credit window control mechanisms defined in classification and credit window flow control mechanisms defined in
[RFC9892] and [RFC9893]. [RFC9892] and [RFC9893].
This document defines a new DLEP Extension Type Value that is used to This document defines a new DLEP Extension Type value that is used to
indicate support for the extension. See Section 2. indicate support for the extension. See Section 2.
1.1. Key Words 1.1. Key Words
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2. Extension Usage and Identification 2. Extension Usage and Identification
The extension defined in this document is composed of the mechanisms The extension defined in this document is built on the mechanisms and
and processing defined in [RFC9892] and [RFC9893]. To indicate that processing defined in [RFC9892] and [RFC9893]. To indicate that the
the Diffserv Aware Credit Window Extension is to be used, an Diffserv Aware Credit Window Extension is to be used, an
implementation MUST include the Diffserv Aware Credit Window Type implementation MUST include the Diffserv Aware Credit Window
Value in the Extensions Supported Data Item (see Section 13.6 of Extension Type value in the Extensions Supported Data Item (see
[RFC8175]). The Extensions Supported Data Item is sent and processed Section 13.6 of [RFC8175]). The Extensions Supported Data Item is
according to [RFC8175]. Any implementation that indicates the use of sent and processed according to [RFC8175]. Any implementation that
the Diffserv Aware Credit Window Extension MUST support all message indicates the use of the Diffserv Aware Credit Window Extension MUST
types, Data Items, the Diffserv Traffic Classification Sub-Data Item, support all message types, Data Items, the Diffserv Traffic
and all related processing defined in [RFC9892] and [RFC9893]. Classification Sub-Data Item, and all related processing defined in
[RFC9892] and [RFC9893].
The Diffserv Aware Credit Window Extension Type Value is 6. See The Diffserv Aware Credit Window Extension Type value is 6. See
Section 5. Section 5.
3. Management Considerations 3. Management Considerations
This section provides several network management guidelines for This section provides several network management guidelines for
implementations supporting the Diffserv Aware Credit Window implementations supporting the Diffserv Aware Credit Window
Extension. Extension.
If this extension is supported, that support MUST be declared using If this extension is supported, that support MUST be declared using
the Extensions Supported Data Item (see Section 13.6 of [RFC8175]). the Extensions Supported Data Item (see Section 13.6 of [RFC8175]).
Diffserv Aware Credit Window Extension Data Items MUST NOT be emitted Diffserv Aware Credit Window Extension Data Items MUST NOT be emitted
by a DLEP participant unless such support was specified in the by a DLEP participant unless such support was specified in the
initialization message received from its peer. The use of the initialization message received from its peer. The use of the
extension defined in this document SHOULD be configurable on both extension defined in this document SHOULD be configurable on both
modems and routers. That configuration can be implemented using a modems and routers. That configuration can be implemented using a
proprietary Command-Line Interface (CLI) or by implementing a YANG proprietary Command-Line Interface or by implementing a YANG module.
module. The definition of the YANG module is out of scope for this The definition of the YANG module is out of scope for this document.
document.
Modems SHOULD support the configuration of mapping a DSCP to a credit Modems SHOULD support the configuration of mapping a DSCP to a credit
window (queue). window (queue).
Modems MAY support the configuration of the number of credit windows Modems MAY support the configuration of the number of credit windows
(queues) to advertise to a router. (queues) to advertise to a router.
Routers may have limits on the number of queues that they can support Routers may have limits on the number of queues that they can support
and limits on supported credit window combinations. Per-destination and limits on supported credit window combinations. Per-destination
queues might not be supported at all. When credit window information queues might not be supported at all. When credit window information
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supported. In either case, any mismatch in capabilities SHOULD be supported. In either case, any mismatch in capabilities SHOULD be
reported to the user via normal network management mechanisms, such reported to the user via normal network management mechanisms, such
as user interface messages or error logging. as user interface messages or error logging.
In all cases, if credit windows are in use, traffic for which credits 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. are not available MUST NOT be sent to the modem by the router.
4. Security Considerations 4. Security Considerations
This document defines a DLEP extension that uses DLEP mechanisms and This document defines a DLEP extension that uses DLEP mechanisms and
the credit window control and flow mechanisms defined in [RFC9892] the credit window flow control mechanisms defined in [RFC9892] and
and [RFC9893]. See also the Security Considerations sections of [RFC9893]. See also the Security Considerations sections of those
those documents. documents.
The defined extension is exposed to vulnerabilities similar to The defined extension is exposed to vulnerabilities similar to
existing DLEP messages and discussed in the Security Considerations existing DLEP messages and discussed in the Security Considerations
section of [RFC8175], such as an injected message resizing a credit section of [RFC8175], such as an injected message resizing a credit
window to a value that results in a denial of service. The security window to a value that results in a denial of service. The security
mechanisms documented in [RFC8175] can be applied equally to the mechanisms documented in [RFC8175] can be applied equally to the
mechanism defined in this document. mechanism defined in this document.
Wildcards for matching Priority Code Point (PCP) and VLAN Identifier Wildcards for matching Priority Code Point (PCP) and VLAN Identifier
(VID) fields (see [RFC9895]) are provided. Note that wildcards may (VID) fields (see [RFC9895]) are provided. Note that wildcards may
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Services", RFC 2475, DOI 10.17487/RFC2475, December 1998, Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,
<https://www.rfc-editor.org/info/rfc2475>. <https://www.rfc-editor.org/info/rfc2475>.
[RFC9895] Wiggins, D., Berger, L., and D. Eastlake 3rd, Ed., [RFC9895] Wiggins, D., Berger, L., and D. Eastlake 3rd, Ed.,
"Dynamic Link Exchange Protocol (DLEP) IEEE 802.1Q Aware "Dynamic Link Exchange Protocol (DLEP) IEEE 802.1Q Aware
Credit Window Extension", RFC 9895, DOI 10.17487/RFC9895, Credit Window Extension", RFC 9895, DOI 10.17487/RFC9895,
November 2025, <https://www.rfc-editor.org/info/rfc9895>. November 2025, <https://www.rfc-editor.org/info/rfc9895>.
Acknowledgments Acknowledgments
The Sub-Data Item format was inspired by Rick Taylor's "Data Item Many useful comments were received from contributors to the MANET
Containers". He also proposed the separation of credit windows from Working Group, notably Ronald in 't Velt.
traffic classification at IETF 98. 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 We had the honor of working too briefly with David Wiggins on this
and related DLEP work. His contribution to the IETF and publication and related DLEP work. His contribution to the IETF and publication
of the first and definitive open-source DLEP implementation have been of the first and definitive open-source DLEP implementation have been
critical to the acceptance of DLEP. We mourn his passing on November critical to the acceptance of DLEP. We mourn his passing on November
26, 2023. We wish to recognize his guidance, leadership, and 26, 2023. We wish to recognize his guidance, leadership, and
professional excellence. We were fortunate to benefit from his professional excellence. We were fortunate to benefit from his
leadership and friendship. He shall be missed. leadership and friendship. He shall be missed.
Authors' Addresses Authors' Addresses
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