Cisco Systems ME3400G2CSA Input and Output Policies

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Cisco ME 3400 EthernetAccess Switch SoftwareConfiguration Guide
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Chapter30 Co nf iguring QoS
Understanding QoS
Step3 Attach the traffic policy to an interface.
You use the service-policy interface configuration command to attach the policy map to an interface for
packets entering or leaving the interface. You must specify whether the traffic policy characteristics
should be applied to incoming or outgoing packets. For exampl e, en terin g t h e service-policy output
class1 interface configuration command attaches all the characteristics of the traf f ic policy n amed class1
to the specified interface. All packets leaving the specified interface are evaluated according to the
criteria specified in the traffic policy named class1.
Input and Output Policies
Policy maps are either input policy maps or output policy maps, attached to packets a s they enter or leav e
the switch by service policies applied to interfaces. Input policy maps usually perform policing and
marking on received traffic. Policed pack ets can be d ropped or redu ced in pr iority (mark ed do wn) i f the y
exceed the maximum permitted rates. Output policy maps perform scheduling and queuing on traffic as
it leaves the switch.
Input policies and output policies have the same basic structure; the difference is in the characteristics
they regulate. Figure30-2 shows the relationship of input and output polic ies.
The maximum number of policy maps that you can configure is 256. You can apply one input policy map
and one output policy map to an interface.
Figure30-2 Input and Output Policy Relationship
Input Policy Maps
Input policy map classification criteria include matching a CoS, a DSCP, or an IP precedence value or
matching an ACL. Input policy maps can have any of these actions:
•Setting or marking a CoS, a DSCP, an IP precedence, or a QoS group value
•Individual policing
•Aggregate policing
Only input policies provide matching on access groups, and only output policies provide matching on
QoS groups. You can assign a QoS group number in an input policy, and match it in the output policy.
The class class-default is used in a policy map for any traffic that does not explicitly match any other
class in the policy map. Input policy maps do not support queuing and scheduling commands, such as
bandwidth, queue-limit, priority, and shape average.
You can configure a maximum of 32 total classes in an input policy.
Ingress
port
Apply
input
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Apply
output
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Switching
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forwarding
Egress
port
Apply
output
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Apply
input
policy