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Managing Excess Bandwidth Distribution for Dynamic CoS on MIC and MPC Interfaces

Service providers often used tiered services that must utilize excess bandwidth as traffic patterns vary. By default, excess bandwidth between a configured guaranteed rate and shaping rate is shared equally among all queues with the same excess priority value, which might not be optimal for all subscribers to a service.

This feature is supported for MIC and MPC interfaces on MX Series routers.

To configure parameters to manage excess bandwidth for subscriber interfaces:

  1. Configure the parameters for the interface.
    1. Configure the guaranteed and shaping rates.
      1. Configure the guaranteed rate:

      2. Configure the shaping rate:


      On MPC/MIC interfaces, the guaranteed rate and the shaping rate share the value specified for the burst size. If the guaranteed rate has a burst size specified, it is used for the shaping rate; if the shaping rate has a burst size specified, it is used for the guaranteed rate. If you have specified a burst for both rates, the system uses the lesser of the two values.

    2. Configure a rate for excess bandwidth.

      You can configure an excess rate for all priorities of traffic:

      Optionally, you can configure an excess rate specifically for high- and low-priority traffic. When you configure the excess-rate statement for an interface, you cannot also configure the excess-rate-low and excess-rate-high statements.

      Best Practice:

      We recommend that you configure either a percentage or a proportion of the excess bandwidth for all schedulers with the same parent in the hierarchy. For example, if you configure interface 1.1 with twenty percent of the excess bandwidth, configure interface 1.2 with eighty percent of the excess bandwidth.

  2. (Optional) Configure parameters for the queue.
    1. Configure the shaping rate.
    2. Configure the excess rate.
    3. (Optional) Configure the priority of excess bandwidth for the queue.

      For queues, you cannot configure the excess rate or excess priority in these cases:

      • When the transmit-rate exact statement is configured. In this case, the shaping rate is equal to the transmit rate and the queue does not operate in the excess region.

      • When the scheduling priority is configured as strict-high. In this case, the queue gets all available bandwidth and never operates in the excess region.

      By default, when traffic exceeds the shaping or guaranteed rates, the system demotes traffic configured with high or medium priority. To disable priority demotion, specify the none option. You cannot configure this option for queues configured with transmit-rate expressed as a percent and when the parent’s guaranteed rate is set to zero.