Users Guide

Enabling QoS Rate Adjustment
By default, while rate limiting, policing, and shaping, the Dell Networking OS does not include the Preamble, SFD, or the IFG elds. These
elds are overhead; only the elds from MAC destination address to the CRC are used for forwarding and are included in these rate
metering calculations.
The Ethernet packet format consists of:
• Preamble: 7 bytes Preamble
• Start frame delimiter (SFD): 1 byte
• 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 elds in rate metering calculations by enabling QoS rate adjustment.
QoS rate adjustment is disabled by default, and no qos-rate-adjust is listed in the running-conguration
• Include a specied 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 elds, know the number of
bytes you want to include.
The default is disabled.
Enabling Strict-Priority Queueing
Strict-priority means that the Dell Networking OS de-queues all packets from the assigned queue before servicing any other queues.
• The strict-priority supersedes bandwidth-percentage and bandwidth-weight percentage congurations.
• A queue with strict priority can starve other queues in the same port-pipe.
• If more than two strict priority queues are congured, the strict priority queue with a higher queue number is scheduled rst.
• Assign strict priority to one unicast queue.
CONFIGURATION mode
strict-priority
The range is from 1 to 3.
Weighted Random Early Detection
The WRED congestion avoidance mechanism drops packets to prevent buering resources from being consumed.
Trac 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 buer and trac manager (BTM) (ingress or egress) can be consumed by only one or a few types of trac, leaving no
space for other types. You can apply a WRED prole to a policy-map so that specied trac can be prevented from consuming too much
of the BTM resources.
WRED uses a prole to specify minimum and maximum threshold values. The minimum threshold is the allotted buer space for specied
trac, for example, 1000KB on egress. If the 1000KB is consumed, packets are dropped randomly at an exponential rate until the maximum
Quality of Service (QoS)
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