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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
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Chapter 33 Configuring QoS
Configuring QoS
(class-based priority queuing). Policing is not supported on output policy maps, except when configuring
priority with police for class-based priority queuing. Output policy map classification criteria are
matching a CoS, DSCP, or IP precedence value or a QoS group.
Follow these guidelines when configuring output policy maps on physical ports:
• Beginning with Cisco IOS Release 12.2(35)SE, you can configure and attach as many output policy
maps as there are ports on the switch. Multiple output policy maps can use the same queue-limit
configuration. However, these policy maps can have only three unique queue-limit configurations.
• Output policy maps can have a maximum of four classes, including the class class-default.
• 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.
Note 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 b y using the speed interface conf igu ration
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 po rt is put in the error-disabled state.