Users Guide

• 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 queue-
based 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