Reference Guide

736 | Quality of Service (QoS)
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QoS Rate Adjustment is disabled by default, and no qos-rate-adjust is listed in the running-configuration.
Strict-priority Queueing
You can assign strict-priority to one unicast queue, 1-7, using the command strict-priority from
CONFIGURATION mode. Strict-priority means that FTOS dequeues all packets from the assigned queue
before servicing any other queues.
• The
strict-priority supersedes bandwidth-percentage an bandwidth-weight percentage
configurations.
• A queue with strict-priority can starve other queues in the same port-pipe.
• On the E-Series, this configuration is applied to the queue on both ingress and egress.
Weighted Random Early Detection
Weighted Random Early Detection is supported only on platform e z
Weighted Random Early Detection (WRED) congestion avoidance mechanism that 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 this case, the space on the BTM (ingress or egress) can be consumed by only one or
a few types of traffic, leaving no space for other types. A WRED profile can be applied 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 will be dropped randomly at an exponential rate until the maximum threshold is reached
(Figure 35-13); this is the “early detection” part of WRED. If the maximum threshold—2000KB, for
example—is reached, then all incoming packets are dropped until less than 2000KB of buffer space is
consumed by the specified traffic.
Task Command Syntax Command Mode
Include a specified number of bytes of packet overhead
to include in rate limiting, policing, and shaping
calculations. For example, to include the Preamble and
SFD, enter qos-rate-adjust 8. For variable length
overhead fields you must know the number of bytes you
want to include.
qos-rate-adjust overhead-bytes
Default: Disabled
C-Series and S-Series Range: 1-31
E-Series Range: 1-144
CONFIGURATION