Administrator Guide

Layer 2 Switching Commands 684
User Guidelines
Strict priority (SP) queues are scheduled in priority order ahead of WRR
queues. Strict priority queues are allocated unlimited bandwidth by default.
Configuring the min-bandwidth on a CoS queue also configured for strict
priority wastes the scheduler slots. Use the cos-queue min-bandwidth
command on lower priority SP and WRR queues to ensure fairness to lower
priority queues by reserving a specific amount of scheduler bandwidth. Use
the show interfaces cos-queue command to display the class of service
settings.
Strict priority scheduling is most useful when it is desirable that low-bit-rate
time-sensitive traffic be queued ahead of other traffic. The administrator
must be careful to limit the bandwidth assigned to the strict priority queue to
avoid potential denial of service attacks. See the “Enterprise Voice VLAN
Configuration With QoS” section in the Users Configuration Guide for a rate
limiting example. If using the min-bandwidth command to reserve
bandwidth on other queues, ensure that the total of the minimum
bandwidths is less than 100% to allow the scheduler to handle bursts of
traffic.
Example
The following example displays how to activate the strict priority scheduler
mode for two queues.
console(config)#cos-queue strict 1 2
The following example displays how to activate the strict priority scheduler
mode for three queues (1, 2, and 4) and reserves a minimal amount of
bandwidth on the other four internal CoS queues (0, 3, 5 and 6).
console(config)#cos-queue strict 1 2 4
console(config)#cos-queue min-bandwidth 5 0 0 10 0 10 10
diffserv
Use the diffserv command in Global Configuration mode to set the DiffServ
operational mode to active. While disabled, the DiffServ configuration is
retained and can be changed, but it is not operational. When enabled,
DiffServ services are operational on queues configured for WRED. To set the
DiffServ operational mode to inactive, use the no form of this command.