In the following example, we create traffic classes and define their match criteria. For the first traffic class (class1), we use access control list (ACL) 101 as match criteria; for the second traffic class (class2), ACL 102. We check the packets against the contents of these ACLs to determine if they belong to the class.

class-map class1
  match access-group 101
  exit
class-map class2
  match access-group 102
  end

In the following example, we define a traffic policy (policy1) containing the QoS features that we will apply to two classes: class1 and class2. The match criteria for these classes were previously defined in Creating a Traffic Class).

For class1, the policy includes a bandwidth allocation request and a maximum packet count limit for the queue reserved for that class. For class2, the policy specifies only a bandwidth allocation request.

policy-map policy1
  class class1
    bandwidth 3000
    queue-limit 30
    exit
  class class2
    bandwidth 2000
    end

The following example shows how to attach an existing traffic policy to an interface. After you define a traffic policy with the policy-map command, you can attach it to one or more interfaces by using the service-policy command in interface configuration mode. Although you can assign the same traffic policy to multiple interfaces, each interface can have only one traffic policy attached in the input direction and only one traffic policy attached in the output direction.

Router(config)# interface TengigabitEthernet 4/1/0
Router(config-if)# service-policy output policy1
Router(config-if)# exit
Router(config)# interface TengigabitEthernet 4/1/0
Router(config-if)# service-policy output policy1
Router(config-if)# end

Use the match not command to specify a QoS policy value that is not used as a match criterion. All other values of that QoS policy become successful match criteria. For instance, if you issue the match not qos-group 4 command in QoS 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:

class-map noip
  match not protocol ip
  end

Traffic that does not meet the match criteria specified in the traffic classes (i.e., unclassified traffic) is treated as belonging to the default traffic class.

If you do not configure a default class, packets are still treated as members of that class. The default class has no QoS features enabled so packets belonging to this class have no QoS functionality. Such packets are placed into a first-in, first-out (FIFO) queue managed by tail drop, which 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 active, packets are dropped until the congestion is eliminated and the queue is no longer full.

The following example configures a policy map (policy1) for the default class (always called class-default) with these characteristics: 10 queues for traffic that does not meet the match criteria of other classes whose policy is defined by class policy1, and a maximum of 20 packets per queue before tail drop is enacted to handle additional queued packets.

policy-map policy1
  class class-default
    fair-queue
    queue-limit 20

In the following example, we configure a policy map (policy1) for the default class (always termed class-default) with these characteristics: 10 queues for traffic that does not meet the match criterion of other classes whose policy is defined by the traffic policy policy1.

policy-map policy1
  class class-default
    shape average 100m

This example shows how packets are evaluated when multiple match criteria exist. It illustrates the difference between the class-map match-any and class-map match-all commands. Packets must meet either all of the match criteria (match-all) or one of the match criteria (match-any) to be considered a member of the traffic class.

The following examples show a traffic class configured with the class-map match-all command:

class-map match-all cisco1
  match protocol ip
  match qos-group 4
  match access-group 101

If a packet arrives on a router with traffic class cisco1 configured on the interface, we assess whether it matches the IP protocol, QoS group 4, and access group 101. If all of these match criteria are met, the packet is classified as a member of the traffic class cisco1 (a logical AND operator; Protocol IP AND QoS group 4 AND access group 101).

class-map match-all vlan 
  match vlan 1
  match vlan inner 1

The following example illustrates use of the class-map match-any command. Only one match criterion must be met for us to classify the packet as a member of the traffic class (i.e., a logical OR operator; protocol IP OR QoS group 4 OR access group 101):

class-map match-any cisco2
  match protocol ip
  match qos-group 4
  match access-group 101

In the traffic class cisco2, the match criterion are evaluated consecutively until a successful match is located. The packet is first evaluated to determine whether the IP protocol can be used as a match criterion. If so, the packet is matched to traffic class cisco2. If not, then QoS group 4 is evaluated as a match criterion and so on. If the packet matches none of the specified criteria, the packet is classified as a member of the default traffic class (class default-class).

There are two reasons to use the match class-map command. One reason is maintenance; if a large traffic class currently exists, using the traffic class match criterion is easier than retyping the same traffic class configuration. The second and more common reason is to mix match-all and match-any characteristics in one traffic policy. This enables you to create a traffic class using one match criterion evaluation instruction (either match-any or match-all) and then use that traffic class as a match criterion in a traffic class that uses a different match criterion type.

Consider this likely scenario: Suppose A, B, C, and D were all separate match criterion, and you wanted traffic matching A, B, or C and D (i.e., A or B or [C and D]) to be classified as belonging to a traffic class. Without the nested traffic class, traffic would either have to match all four of the match criterion (A and B and C and D) or match any of the match criterion (A or B or C or D) to be considered part of the traffic class. You would not be able to combine “and” (match-all) and “or” (match-any) statements within the traffic class; you would be unable to configure the desired configuration.

The solution: Create one traffic class using match-all for C and D (which we will call criterion E), and then create a new match-any traffic class using A, B, and E. The new traffic class would have the correct evaluation sequence (A or B or E, which is equivalent to A or B or [C and D]).