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The Modular QoS CLI (MQC) Unconditional Packet Discard feature allows customers to classify traffic matching certain criteria and then configure the system to unconditionally discard any packets matching that criteria. The Modular QoS CLI (MQC) Unconditional Packet Discard feature is configured using the Modular Quality of Service Command-Line Interface (MQC) feature. Packets are unconditionally discarded by using the new drop command within the MQC.
This feature allows you to discard (drop), without any further system processing, the packets of a particular class. This function is very useful when you want to discard all the packets for nonessential applications (for instance, Internet browsing applications or unauthorized video applications) and allocate system resources to more essential applications. This feature allows the user to discard those nonessential packets and simultaneously obtain the bit and drop rate statistics for that particular class and the traffic within that class. The statistics are gathered through the CISCO-CLASS-BASED-QOS-MIB.
Packets are unconditionally discarded by configuring the drop action inside a traffic class (inside of a policy map). This drop action is accomplished with the new drop command. Note the following restrictions for configuring the drop action within a traffic class:
The discarding action is the only action that can be configured in a traffic class. That is, no other actions can be configured in the traffic class.
When a traffic class is configured with the drop command, a "child" (nested) policy cannot be configured for this specific traffic class through the servicepolicy command.
The discarding action cannot be configured for the default class known as the class-default class.
Related Features and Technologies
Modular quality of service command-line interface (MQC)
"Applying QoS Features Using the MQC" module
"Classifying Network Traffic" module
"Marking Network Traffic" module
Cisco IOS Quality of Service Solutions Command Reference
Supported Standards MIBs and RFCs
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Specifies the name of the class map to be created. If match-all or match-any is not specified, traffic must match all the match criteria to be classified as part of the traffic class. Enters class-map configuration mode.
Specifies that traffic matching the specified access group will be placed in the map class created above. This command provides just an example of the match criterion you can specify. For more information about the additional match criteria available, see the "Applying QoS Features Using the MQC" module.
Exits from the configuration mode.
Creating a Policy Map
Command or Action
Specifies the name of the policy map to be created. Enters policy-map configuration mode.
Specifies the name of the traffic class configured earlier in the Configuring the Class Map section above. This traffic class is used to classify traffic to the policy map. Enters policy-map class configuration mode.
Discards the packets in the specified traffic class.
Exits policy-map configuration mode.
Attaching the Policy Map to an Interface or a VC
Example Configuring the Discard Action Configuration in a Traffic Class
In the following sample configuration, a traffic class called "class1" has been created and configured for use in a policy-map called "policy1." The policy-map policy1 is attached to an output serial interface 2/0. All packets matching access-group 101 are placed in a class called "c1." Packets belonging to this class are discarded.
Router(config)# class-map class1
Router(config-cmap)# match access-group 101
Router(config-cmap)# policy-map policy1
Router(config-pmap)# class c1
Router(config-pmap-c)# interface s2/0
Router(config-if)# service-policy output policy1
The following sample output of the showpolicy-map command displays the contents of the policy map called "policy1." All the packets belonging to the class called "c1" are discarded.
Router# show policy-map policy1
Policy Map policy1
Example Verifying the Discard Action Configuration in the Policy Map
The following sample output of the showpolicy-mapinterface command displays the statistics for the Serial2/0 interface, to which a policy map called "policy1" is attached. The discard action has been specified for all the packets belonging to a class called "c1." In this example, 32000 bps of traffic is sent ("offered") to the class and all of them are dropped. Therefore, the drop rate shows 32000 bps.
Router# show policy-map interfaceSerial2/0
Service-policy output: policy1
Class-map: c1 (match-all)
10184 packets, 1056436 bytes
5 minute offered rate 32000 bps, drop rate 32000 bps
Match: ip precedence 0