• Destination MAC address: 6 bytes• Source MAC address: 6 bytes• Ethernet Type/Length: 2 bytes• Payload: (variable)• Cyclic redundancy check (CRC): 4 bytes• Inter-frame gap (IFG): (variable)You can optionally include overhead fields in rate metering calculations by enabling QoS rate adjustment.QoS rate adjustment is disabled by default.• Specify the number of bytes of packet overhead to include in rate limiting, policing, and shaping calculations.CONFIGURATION modeqos-rate-adjust overhead-bytesFor example, to include the Preamble and SFD, type qos-rate-adjust 8. For variable length overhead fields, know thenumber of bytes you want to include.The default is disabled.Enabling Strict-Priority QueueingStrict-priority means that Dell Networking OS de-queues all packets from the assigned queue before servicing any other queues.• The strict-priority supersedes bandwidth-percentage configuration.• A queue with strict priority can starve other queues in the same port-pipe.• Assign strict priority to one unicast queue.CONFIGURATION modestrict-priorityThe range is from 1 to 3.Weighted Random Early DetectionThe WRED congestion avoidance mechanism drops packets to prevent buffering resources from being consumed.Traffic is a mixture of various kinds of packets. The rate at which some types of packets arrive might be greater than others. In thiscase, 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 fromconsuming 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 forspecified traffic, for example, 1000KB on egress. If the 1000KB is consumed, packets are dropped randomly at an exponential rateuntil the maximum threshold is reached (as shown in the following illustration); this procedure is the “early detection” part of WRED.If the maximum threshold, for example, 2000KB, is reached, all incoming packets are dropped until the buffer space consumes lessthan 2000KB of the specified traffic.592 Quality of Service (QoS)
