Class of Service
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Support for drop congestion notification (QFX5240-64OD, QFX5240-64QD, QFX5241-64OD, QFX5241-64QD, and QFX5241E-64OD)—QFX5240 and QFX5241 switches support drop congestion notification (DCN) to enhance congestion management. DCN is a congestion management technique based on packet trimming. Rather than drop a packet when congestion occurs, the device trims the packet’s payload, which results in a smaller packet. The device then transmits this smaller packet through a high-priority queue toward its destination. Subsequent hops in the network must recognize DCN-drop marked packets and direct them to high-priority queues as well. End hosts must process the trimmed DCN packets, identify the packets dropped due to congestion, and request retransmission of those lost packets.
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Rewrite outer DSCP, preserve ECN, and copy inner DSCP by default in EVPN-VXLAN (QFX5130-32CD, QFX5130-48C, QFX5130-48CM, QFX5130E-32CD, QFX5700, and QFX5700E)—You can control DSCP marking on network-facing underlay interfaces in EVPN-VXLAN by assigning one rewrite rule per interface for IPv4 and IPv6. By default, the device copies inner DSCP to the outer VXLAN header. A DSCP rewrite overrides the type-of service (ToS) copy and rewrites only the outer IP DSCP, preserving inner IP DSCP and ECN bits. The device does not support 802.1p rewrite. You can enable explicit congestion notification (ECN) per output queue through scheduler configuration. With weight random early detection (WRED), congested queues mark packets CE (congestion experienced) when all intermediate devices enable ECN. Use this capability to maintain QoS consistency across overlays and underlays.
[See CoS Support on EVPN VXLANs.]
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DCBX support for PFC (QFX5130-32CD, QFX5130E-32CD, QFX5130-48C, QFX5130-48CM, QFX5220, QFX5230-64CD, QFX5240-64OD, QFX5240-64QD, QFX5700, and QFX5700E)—We support data center bridging and exchange capability (DCBX) support for priority-based flow control (PFC) on the listed switches.
[See Understanding DCBX and priority-flow-control.]
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Dynamic threshold profiles for shared buffer pools (QFX5130-32CD, QFX5130-48C, QFX5130-48CM, QFX5130E-32CD, QFX5220, QFX5230-64CD, QFX5240-64OD, and QFX5240-64QD)—You can tune the buffer allocated per priority group or port based on the dynamic threshold setting, also known as the alpha value. Existing design supports this feature through a global configuration that is applicable to all the ports on the device regardless of the port configuration or properties. Having a global alpha value is not effective when the device has ports operating at various speeds. With this feature, you can create dynamic thresholds per priority group and then associate the dynamic threshold profile on an ingress interface. This configuration creates interface-specific threshold values.
You can configure per priority group dynamic thresholds for each interface to optimize shared buffer allocation and protect lossless traffic during congestion. Egress lossless queues inherit ingress priority-group alpha values.