Caveats for Configuring CoS for Aggregated Interfaces

There are some restrictions and caveats when you configure CoS on aggregated Ethernet and SONET/SDH interfaces:

• Chassis scheduling, described in Scheduling Packet Forwarding Component Queues, is not supported on aggregated interfaces, because a chassis scheduler applies to the entire PIC and not just to one interface.
• Per-unit scheduling, described in Associating a Scheduler Map with a DLCI or VLAN, is not supported on aggregated interfaces. Furthermore, you cannot configure per-unit scheduling on any member link in an aggregated interface.
• An aggregated interface is a pseudo-interface. Therefore, CoS queues are not associated with the aggregated interface. Instead, CoS queues are associated with the member link interfaces of the aggregated interface.
• When you apply CoS parameters to the aggregated interface, they are applied to the CoS queues of the member link interfaces. You can apply CoS classifiers and rewrite rules directly to the member link interfaces, and the software uses the values you configure.
• When you apply scheduler maps to member link interfaces, the software cannot always use the values you configure because the speed of the aggregated interface is the sum of the speeds of its member link interfaces.

When the scheduler map of the aggregate interface has schedulers configured for absolute transmit rate, the scheduler for the member link interfaces is scaled to the speed of each member link interface. Each member link interface has an automatic scheduler map that is not visible in the CLI. This scheduler map is allocated when the member link is added to the aggregate interface and is deleted when the member link is removed from the aggregate interface.

• If you configure the scheduler transmit rate of the aggregate interface as an absolute rate, the software uses the following formula to scale the transmit rate of each member link:

transmit rate of member link interface = 

(configured transmit rate of aggregate interface / 

total speed of aggregate interface) * 

(total speed of member link interface / total configured percent) * 100

• If you configure the scheduler transmit rate of the aggregate interface as a percentage, the software uses the following formula to scale the transmit rate of each member link:

transmit rate percent of member link interface = 

(configured transmit rate percent of aggregate interface / 

total configured percent) * 100

The total configured percent is the sum of the configured transmit rate of all schedulers in terms of percentage of the total speed of the aggregate interface.

For more information, see Examples: Configuring CoS for Aggregated Ethernet and SONET/SDH Interfaces.

• All the other parameters for the schedulers, including priority, drop profile, and buffer size, are copied without change from the scheduler of the aggregated interface to the member link interfaces.
• The configuration related to the logical interfaces, including classifiers and rewrite rules, is copied from the aggregated logical interface configuration to the member link logical interfaces.
• For the scheduler map applied to an aggregated interface, if you configure a transmission rate in absolute terms, then the traffic of all the member link interfaces might be affected if any of the member link interfaces go up or down.