can be associated with a single traffic class using the match any command. The match not command inverts the specified condition. This command specifies a match criterion value that prevents packets from being classified as members of a specified traffic class. All other values of that particular match criterion belong to the class. At least one match command should be used within the class-map configuration mode. The description command is used for documenting a comment about the class map. There are many ways to classify traffic when configuring class maps. Figure shows one possible way to classify traffic using access control lists (ACLs) to specify the traffic that needs to match for the QoS policy. Class maps support standard ACLs and extended ACLs. The match access-group command allows an ACL to be used as a match criterion for traffic classification. Example: Traffic Classes Defined
In the following example, two traffic classes are created and their match criteria are defined. For the first traffic class called class1, access control list (ACL) 101 is used as the match criterion. For the second traffic class called class2, ACL 102 is used as the match criterion. The router checks the packets against the contents of these ACLs to determine if they belong to the class. Router(config)# class-map class1
Router(config-cmap)# match access-group 101
Router(config-cmap)# exit
Router(config)# class-map class2
Router(config-cmap)# match access-group 102
Router(config-cmap)# exit Example: match not Command
The match not command is used to specify a specific QoS policy value that is not used as a match criterion. When using the match not command, all other values of that QoS policy become successful match criteria. For instance, if the match not qos-group 4 command is issued in class-map configuration mode, the specified class will accept all QoS group values except 4 as successful match criteria. In the following traffic class, all protocols except IP are considered successful match criteria: Router(config)# class-map noip
Router(config-cmap)# match not protocol ip
Router(config-cmap)# exit
Content 3.4 Using MQC for Implementing QoS 3.4.5 Step 2: Configuring Policy Maps Figure describes the concept of a policy map. The policy-map command creates a traffic policy. The purpose of a traffic policy is to configure the QoS features that should be associated with the traffic which are then classified into a traffic class or classes. You can then assign as much bandwidth or set whatever priority you need to that class. A traffic policy contains three elements: a case-sensitive name, a traffic class (specified with the class command), and the QoS policies. The policy-map command specifies the name of a traffic policy (for example, issuing the policy-map class1 command would create a traffic policy named class1). After you issue the policy-map command, you enter policy-map configuration mode. You can then enter the name of a traffic class. You must be in the policy-map configuration mode to enter QoS features that apply to the traffic matching the named class. A packet can match only one traffic class within a traffic policy. If a packet matches more than one traffic class in the traffic policy, the first traffic class defined in the policy is used. On the other hand, the Cisco MQC does not necessarily require that you associate only one traffic class to a single traffic policy. When packets match to more than one match criterion, multiple traffic classes can be associated with a single traffic policy. The next topic will explain the concept of nested class maps. You configure service policies with the policy-map command. One policy map can have up to 256 classes using the class command with the name of a preconfigured class map. Figure shows the policy-map and class command syntax. A nonexistent class can also be used within the policy-map configuration mode if the match condition is specified after the name of the class. The running configuration will reflect such a configuration by using the match-any strategy and inserting a full class map configuration. The Configuration Modes table shows starting and resulting configuration modes for the class-map, policy-map, and class commands. Configuration Modes
Staring Configuration Mode Command Resulting Configuration Mode Router(config)# class-map Router(config-cmap)# Router(config)# policy-map Router(config-pmap)# Router(config-pmap)# class Router(config-pmap-c)# All traffic not identified in any of the class maps that are used within the policy map, become part of the default class “class-default.” This class has no QoS guarantees by default. The default class, when used on output, can use one FIFO queue or flow-based WFQ. The default class is part of every policy map, even if a default class is not included in the configuration. Example: Traffic Policy Created
In the following example, a traffic policy called policy1 is defined to contain policy specifications for the two classes—class1 and class2. The match criteria for these classes were defined in the traffic classes. For class1, the policy includes a bandwidth allocation request and a maximum packet count limit for the queue reserved for the class. For class2, the policy specifies only a bandwidth allocation request. Router(config)# policy-map policy1
Router(config-pmap)# class class1
Router(config-pmap-c)# bandwidth 3000
Router(config-pmap-c)# queue-limit 30
Router(config-pmap)# exit
Router(config-pmap)# class class2
Router(config-pmap-c)# bandwidth 2000
Router(config-pmap)# exit Example: Enforcing a Sub-rate
In this example, you need to enforce a sub-rate (that is, 10 Mbps virtual pipe on a 1 Gbps link) on a particular link, while offering minimum bandwidth guarantees to applications such as voice, mission critical applications, and video within that virtual pipe as follows: Below is the sample configuration. Router(config)# policy-map CHILD
Router(config-pmap)# class VOICE
Router(config-pmap-c)# priority 1000
Router(config-pmap-c)# class MCA
Router(config-pmap-c)# bandwidth 2000
Router(config-pmap-c)# class VIDEO
Router(config-pmap-c)# bandwidth 5000
Router(config)# policy-map PARENT
Router(config-pmap)# class class-default
Router(config-pmap-c)# shape average 10000000
Router(config-pmap-c)# service-policy CHILD Note
If a particular application does not use the bandwidth, it can be shared among the active applications, therefore no bandwidth is wasted. Example: Default Traffic Class Configuration
Unclassified traffic (traffic that does not meet the match criteria specified in the traffic classes) is treated as belonging to the default traffic class. If the user does not configure a default class, packets are still treated as members of the default class. However, by default, the default class has no enabled features. Therefore, packets belonging to a default class with no configured features have no QoS functionality. These packets are then placed into a FIFO queue and forwarded at a rate determined by the available underlying link bandwidth. This FIFO queue is managed by tail drop. (Tail drop is a means of avoiding congestion that treats all traffic equally and does not differentiate between classes of service. Queues fill during periods of congestion. When the output queue is full and tail drop is in effect, packets are dropped until the congestion is