Command:

class (policy-map)


Mode:

Router(config-pmap-c)#


Syntax:

class {class-name | class-default}

no class {class-name | class-default}

 

Syntax Description:

class-name The name of the class for which you want to configure or modify policy.
class-default Specifies the default class so that you can configure or modify its policy.

 

Command Description:

To specify the name of the class whose policy you want to create or change or to specify the default class (commonly known as the class-default class) before you configure its policy, use the class QoS policy-map configuration command. To remove a class from the policy map, use the no form of this command.

Enter the policy-map command to identify the policy map and enter QoS policy-map configuration mode before you use the class command. After you specify a policy map, you can configure policy for new classes or modify policy for any existing classes in that policy map.

The class name that you specify in the policy map ties the characteristics for that class�that is, its policy�to the class map and its match criteria, as configured using the class-map command.

When you configure policy for a class and specify its bandwidth and attach the policy map to an interface, class-based weighted fair queueing (CBWFQ) determines if the bandwidth requirement of the class can be satisfied. If so, CBWFQ allocates a queue for the bandwidth requirement.

When a class is removed, available bandwidth for the interface is incremented by the amount previously allocated to the class.

The maximum number of classes you can configure for a router�and, therefore, within a policy map�is 64.

The predefined default class called class-default is the class to which traffic is directed if that traffic does not satisfy the match criteria of other classes whose policy is defined in the policy map.

You can define a class policy to use either tail drop (by using the queue-limit command) or Weighted Random Early Detection (WRED) packet drop (by using the random-detect command). The queue-limit and random-detect commands cannot be used in the same class policy, but they can be used in two class policies in the same policy map.

You can configure the bandwidth command when either the queue-limit or the random-detect command is configured in a class policy. The bandwidth command specifies the amount of bandwidth allocated for the class.

For the default class, you can configure the fair-queue (class-default) command. The fair-queue command specifies the number of dynamic queues for the default class. The fair-queue command can be used in the same class policy as either the queue-limit or random-detect command. It cannot be used with the bandwidth command.


Example:

The following example configures three class policies included in the policy map called policy1. Class1 specifies policy for traffic that matches access control list 136. Class2 specifies policy for traffic on interface ethernet101. The third class is the default class to which packets that do not satisfy configured match criteria are directed.

! The following commands create class-maps class1 and class2
! and define their match criteria:
class-map class1
 match access-group 136
class-map class2
 match input-interface ethernet101
! The following commands create the policy map, which is defined to contain policy
! specification for class1, class2, and the default class:
policy-map policy1
class class1
 bandwidth 2000
 queue-limit 40
class class2
 bandwidth 3000
 random-detect
 random-detect exponential-weighting-constant 10
class class-default
 fair-queue 16
 queue-limit 20


Misconceptions:

None.


Related Commands:

class-map

policy-map

queue-limit

random-detect (interface)


� Cisco Systems, Inc. 2001, 2002, 2003
World Wide Education

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