Supported Platforms
Related Documentation
- QFabric System, QFX Series standalone switches
- Understanding CoS Output Queue Schedulers
- Understanding CoS Traffic Control Profiles
- Example: Configuring CoS Hierarchical Port Scheduling (ETS)
- Example: Configuring Queue Schedulers
- Example: Configuring Traffic Control Profiles (Priority Group Scheduling)
- Defining CoS Queue Schedulers
- Defining CoS Traffic Control Profiles (Priority Group Scheduling)
Understanding CoS Priority Group Shaping and Queue Shaping (Maximum Bandwidth)
If the amount of traffic on an interface exceeds the maximum bandwidth of the interface, it leads to congestion. You can use priority group (forwarding class set) shaping and queue shaping to manage the excess traffic and avoid congestion.
The maximum bandwidth sets the most bandwidth a priority group or a queue can use after all of the priority group and queue minimum bandwidth requirements are met, even if more bandwidth is available.
This topic covers:
Priority Group Shaping
Priority group shaping enables you to shape the aggregate traffic of a forwarding class set on a port to a maximum rate that is less than the line or port rate. The maximum bandwidth (shaping-rate) that you configure for a priority group sets the maximum bandwidth available to all of the forwarding classes (queues) in the forwarding class set.
If a port has more than one priority group and the combined shaping-rate value of the priority groups is greater than the amount of port bandwidth available, the bandwidth is shared proportionally among the priority groups.
You configure the priority group shaping-rate in the traffic control profile.
Queue Shaping
Queue shaping throttles the rate at which queues transmit packets. For example, using queue shaping, you can rate-limit a strict-high priority queue so that the strict-priority queue does not lock out (or starve) low-priority queues.
![]() | Note: We recommend that you always apply a shaping rate to strict-high priority queues to prevent them from starving other queues. If you do not apply a shaping rate to limit the amount of bandwidth a strict-high priority queue can use, then the strict-high priority queue can use all of the available port bandwidth and starve other queues on the port. |
Similarly, for any queue, you can configure queue shaping (shaping-rate) to set the maximum bandwidth for a particular queue.
The shaping-rate value of the priority group sets the aggregate maximum amount of bandwidth available to the queues that belong to the priority group. The cumulative total bandwidth the queues consume cannot exceed the maximum bandwidth of the priority group to which they belong on a port.
If a priority group has more than queue and the combined shaping-rate value of the queues is greater than the amount of bandwidth available to the priority group, the bandwidth is shared proportionally among the queues.
You configure the queue shaping-rate in the scheduler configuration.
Shaping Maximum Bandwidth Using Hierarchical Scheduling
Priority group shaping defines the maximum bandwidth allocated to a forwarding class set on a port, whereas queue shaping defines a limit on maximum bandwidth usage per queue. The queue bandwidth is a portion of the priority group bandwidth.
Figure 1 shows how the port bandwidth is allocated to priority groups (forwarding class sets) based on the shaping rate of each priority group, and how the bandwidth of each priority group is allocated to the queues in the priority group based on the shaping rate of each queue.
Figure 1: Setting Maximum Bandwidth Using Hierarchical Scheduling

Related Documentation
- QFabric System, QFX Series standalone switches
- Understanding CoS Output Queue Schedulers
- Understanding CoS Traffic Control Profiles
- Example: Configuring CoS Hierarchical Port Scheduling (ETS)
- Example: Configuring Queue Schedulers
- Example: Configuring Traffic Control Profiles (Priority Group Scheduling)
- Defining CoS Queue Schedulers
- Defining CoS Traffic Control Profiles (Priority Group Scheduling)
Published: 2014-07-23
Supported Platforms
Related Documentation
- QFabric System, QFX Series standalone switches
- Understanding CoS Output Queue Schedulers
- Understanding CoS Traffic Control Profiles
- Example: Configuring CoS Hierarchical Port Scheduling (ETS)
- Example: Configuring Queue Schedulers
- Example: Configuring Traffic Control Profiles (Priority Group Scheduling)
- Defining CoS Queue Schedulers
- Defining CoS Traffic Control Profiles (Priority Group Scheduling)