Dynamic Link Exchange Protocol (DLEP) IEEE 802.1Q Aware Credit Window Extension
Extracted elements (20)
This extension builds on RFC 9892 (Traffic Classification Data Item) and RFC 9893 (Credit-Based Flow Control Messages and Data Items) rather than defining its own independent mechanism, enabling a layered approach where IEEE 802.1Q awareness is an additive capability. The companion Diffserv-based approach is in RFC 9894.
When both Diffserv and Ethernet traffic classification are applied to a flow, Ethernet-based classification takes precedence, as specified in Section 2.3.1 of RFC 9892.
Any implementation that indicates use of 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 RFC 9892 and RFC 9893.
Any mismatch in capabilities SHOULD be reported to the user through standard network management mechanisms, such as user interface notifications or error logging.
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.
If the credit window information provided by the modem exceeds the router's capabilities, the router SHOULD utilize a subset of the advertised credit windows, or alternatively MAY reset the session and indicate the extension is not supported.
If this extension is supported, that support MUST be declared using the Extensions Supported Data Item (RFC 8175 Section 13.6), which is configurable on both modems and routers.
It is RECOMMENDED that wildcards not be used for PCP and VID matching unless clearly needed, as they may inadvertently match unexpected or new flows.
Modems MAY support per-VLAN PCP-to-credit-window mapping. VID 0x0000 indicates the VID is ignored, VID 0xFFFF is reserved, and VIDs 0x0001 through 0xFFFE may be used in traffic classification.
Modems SHOULD support the configuration of mapping a PCP to a credit window (queue).
Regardless of implementation, if credit windows are in use, the router MUST NOT send traffic to the modem unless sufficient credits are available.
The use of the extension defined in this document SHOULD be configurable on both modems and routers.
To indicate use of the IEEE 802.1Q Aware Credit Window Extension, an implementation MUST include the IEEE 802.1Q Aware Credit Window Extension Type value in the Extensions Supported Data Item as defined in Section 13.6 of RFC 8175.
When VLANs are supported by a modem without PCP support, the modem SHOULD support the configuration of mapping a VLAN to a credit window (queue).
Credit window classification is based on DLEP destinations, IEEE 802.1Q VLANs (12-bit VID field), and Priority Code Points (3-bit PCP field). Credit windows may be shared across multiple destinations, VLANs, and PCPs, or dedicated to a specific combination.
The extension introduces an Ethernet-based flow control mechanism using one or more logical credit windows, each typically associated with a virtual or physical queue. The router uses traffic flow classification from the modem to assign traffic to the appropriate credit window.
The extension supports wildcard matching for any PCP value or any VID value, allowing a single credit window rule to apply broadly across multiple classified flows.
IANA has assigned Extension Type Value 5 in the 'Extension Type Values' registry within the 'Dynamic Link Exchange Protocol (DLEP) Parameters' registry group, with description 'IEEE 802.1Q Aware Credit Window'.
PCP and VID wildcard matching may inadvertently match unexpected packet flows or new flows that appear after wildcard matching has been configured, potentially allowing unintended traffic to consume or be blocked by credit windows.
The extension inherits DLEP vulnerabilities discussed in RFC 8175, including the risk of an injected message resizing a credit window to a value that causes a denial of service. The security mechanisms from RFC 8175 apply equally to this extension.