Users Guide

Enabling QoS Rate Adjustment
By default while rate limiting, policing, and shaping, Dell Networking OS does not include the Preamble, SFD,
or the IFG fields. These fields are overhead; only the fields 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 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 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
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 configuration.
• A queue with strict priority can starve other queues in the same port-pipe.
• Assign strict priority to one unicast queue.
CONFIGURATION mode
Quality of Service (QoS) 764