Enabling Strict-Priority Queueing; Weighted Random Early Detection - Dell S4820T Configuration Manual

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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 mode

qos-rate-adjust overhead-bytes

For example, to include the Preamble and SFD, type 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

Strict-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 mode

strict-priority

The range is from 1 to 3.

The WRED congestion avoidance mechanism drops packets to prevent buffering resources from being

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 detection" part of WRED. If the maximum

threshold, for example, 2000KB, is reached, all incoming packets are dropped until the buffer space

consumes less than 2000KB of the specified traffic.

Quality of Service (QoS)