Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 776

• Include a specified number of bytes of packet overhead to include in rate limiting, policing, and shaping calculations. CONFIGURATION mode qos-rate-adjust overhead-bytes For example, to include the Preamble and SFD, enter qos-rate-adjust 8. For variable length overhead fields, know the number of bytes you want to include. The default is disabled. The range is from 1 to 31. Enabling Strict-Priority Queueing In strict-priority queuing, the system de-queues all packets from the assigned queue before servicing any other queues. You can assign strict-priority to one unicast queue, using the strict-priority command. • Policy-based per-queue rate shaping is not supported on the queue configured for strict-priority queuing. To use queuebased rate-shaping as well as strict-priority queuing at the same time on a queue, use the Scheduler Strict feature as described in Scheduler Strict. • The strict-priority supersedes bandwidth-percentage and bandwidth-weight percentage configurations. • A queue with strict priority can starve other queues in the same port-pipe. NOTE: Assigning strict priority scheduling to a unicast queue on all ports using a global command is not supported. However, you can configure both unicast and multicast queue belonging to a dot1p to use strict priority scheduling using policy maps and then associate the policy map to the egress interface. Weighted Random Early Detection Weighted random early detection (WRED) is a congestion avoidance mechanism that drops packets to prevent buffering resources from being consumed. NOTE: On the switch, WRED and Explicit Congestion Notification (ECN) marking are supported on front-end I/O and backplane HiGig ports. When you enable WRED, packets are dropped during times of network congestion based on the configured minimum and maximum WRED thresholds. ECN marks packets for later transmission (instead of dropping them) when the network recovers from a heavy traffic condition. For information about how to configure weights for WRED and ECN operation, see Configuring Weights and ECN for WRED. Traffic is a mixture of various kinds of packets. The rate at which some types of packets arrive might be greater than others. In this case, the space on the buffer and traffic manager (BTM) (ingress or egress) can be consumed by only one or a few types of traffic, leaving no space for other types. You can apply a WRED profile to a policy-map so that specified traffic can be prevented from consuming too much of the BTM resources. WRED uses a profile to specify minimum and maximum threshold values. The minimum threshold is the allotted buffer space for specified traffic, for example, 1000KB on egress. If the 1000KB is consumed, packets are dropped randomly at an exponential rate until the maximum threshold is reached (as shown in the following illustration); this procedure is the "early Quality of Service (QoS) 776