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Configuring QoS
Configuring QoS
All output policy maps must have the same number of defined class-maps defined, either 1, 2, or 3.
All output policy maps must use the same set of classes, although the actions for each class can differ for each
output policy map.
In a child policy map, the class-default supports all output policy map actions except priority and police. Action
restrictions for class-default are the same as for other classes except that a queue limit configuration for
class-default does not require a scheduling action.
To classify based on criteria at the output, the criteria must be established at the input. You can establish criteria at
the input through classification only when you configure only policing and not marking, or through explicit marking
when you configure any marking (policing with conform or exceed marking or unconditional set marking).
You cannot configure class-based priority queuing under the class class-default in an output policy map
In an output policy map, unless priority queuing is configured, the class default receives a minimum bandwidth
guarantee equal to the unconfigured bandwidth on the port.
After you have attached an output policy map to an interface by using the service-policy interface configuration
command, you can change only the parameters of the configured actions (rates, percentages, and so on) or add or
delete classification criteria of the class map while the policy map is attached to the interface. To add or delete a
class or action, you must detach the policy map from all interfaces, modify it, and then reattach it to interfaces.
If you anticipate that you might need three classes in a policy map, you should define three classes when you
create the policy map, even if you are not ready to use all three at that time. You cannot add a class to a policy
map after it has been attached to an interface.
When at least one output policy map is attached to a active port, other active ports without output policy maps
attached might incorrectly schedule and incorrectly order traffic that uses the same classes as the attached output
policy maps. We recommend attaching output policy maps to all ports that are in use. We also recommend putting
any unused ports in the shutdown state by entering the shutdown interface configuration command. For example,
if you attach an output policy map that shapes DSCP 23 traffic to a port, DSCP traffic that is sent out of any other
port without a policy map attached could be incorrectly scheduled or ordered incorrectly with respect to other traffic
sent out of the same port.
We strongly recommended that you disable port speed autonegotiation when you attach an output policy map to a
port to prevent the port from autonegotiating to a rate that would make the output policy map invalid. You can
configure a static port speed by using the speed interface configuration command. If an output policy-map is
configured on a port that is set for autonegotiation and the speed autonegotiates to a value that invalidates the policy,
the port is put in the error-disabled state.
You can attach only one output policy map per port.
The maximum number of policy maps configured on the switch is 256.
These sections describe how to configure different types of output policy maps:
Configuring Output Policy Maps with Class-Based-Weighted-Queuing, page 630
Configuring Output Policy Maps with Class-Based Shaping, page 631
Configuring Output Policy Maps with Port Shaping, page 632
Configuring Output Policy Maps with Class-Based Priority Queuing, page 633
Configuring Output Policy Maps with Weighted Tail Drop, page 637
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