Applying QoS Features Using the MQC

The MQC structure allows you to define a traffic class, create a traffic policy, and attach the traffic policy to an interface.

Available match Commands

The table below lists some of the available match commands that can be used with the MQC. The available match commands vary by Cisco IOS release and platform. For more information about the commands and command syntax, see the command reference for the Cisco IOS release and platform that you are using.

If the traffic class contains more than one match command, you need to specify how to evaluate the match commands. You specify this by using either the match-any or match-allkeywords of the class-map command. Note the following points about the match-any and match-all keywords:

• If you specify the match-anykeyword, the traffic being evaluated by the traffic class must match one of the specified criteria.
• If you specify the match-all keyword, the traffic being evaluated by the traffic class must match all of the specified criteria.
• If you do not specify either keyword, the traffic being evaluated by the traffic class must match all of the specified criteria (that is, the behavior of the match-all keyword is used).

Note	The match coscommand is shown in Step 4. The match cos command is simply an example of one of the match commands that you can use. For information about the other available match commands, see Creating a Traffic Class Using the MQC.

Note	The bandwidth command is shown in Step 5. The bandwidth command is simply an example of one of the commands that you can use in a policy map. For information about other available commands, see Creating a Traffic Policy Using the MQC.

The traffic policy (policy map) applies the enabled QoS feature to the traffic class once you attach the policy map to the interface (by using the service-policy command). For information about the input and output keywords of the service-policy command, see the input and output Keywords of the service-policy Command.

Depending on the platform and Cisco IOS release that you are using, a traffic policy can be attached to an ATM permanent virtual circuit (PVC) subinterface, a Frame Relay data-link connection identifier (DLCI), or another type of interface.

To attach a traffic policy to an interface, complete the following steps.

Note

Multiple traffic policies on tunnel interfaces and physical interfaces are not supported if the interfaces are associated with each other. For instance, if a traffic policy is attached to a tunnel interface while another traffic policy is attached to a physical interface--with which the tunnel interface is associated--only the traffic policy on the tunnel interface works properly. The amount of bandwidth allocated to the priority traffic cannot exceed the amount of bandwidth available on the interface. If the traffic policy is configured such that the amount of bandwidth allocated to the priority traffic exceeds the amount of bandwidth available on the interface, the traffic policy will be suspended. Previously, the policy map would have been rejected. Now that it is only suspended, you have the option of modifying the traffic policy accordingly and then reattaching the traffic policy to the interface.

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. Packets are checked 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)# end

In the following example, a traffic policy called policy1 is defined. The traffic policy contains the QoS features to be applied to two classes--class1 and class2. The match criteria for these classes were previously defined (as described in the Example Creating a Traffic Class).

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-c)# exit
Router(config-pmap)# class class2
Router(config-pmap-c)# bandwidth 2000
Router(config-pmap-c)# 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 ethernet1/1
Router(config-if)# service-policy output policy1
Router(config-if)# exit
Router(config)# interface fastethernet1/0/0
Router(config-if)# service-policy output policy1
Router(config-if)# exit

The match notcommand 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)# end

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 you do not configure a default class, packets are still treated as members of the default class. However, by default, the default class has no QoS features enabled. Therefore, packets belonging to a default class have no QoS functionality. These packets are placed into a first-in, first-out (FIFO) queue 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 eliminated and the queue is no longer full.

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

Router(config)# policy-map policy1
Router(config-pmap)# class class-default
Router(config-pmap-c)# fair-queue
Router(config-pmap-c)# queue-limit 20

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

The following example shows a traffic class configured with the class-map match-allcommand:

Router(config)# class-map match-all cisco1
Router(config-cmap)# match protocol ip
Router(config-cmap)# match qos-group 4
Router(config-cmap)# match access-group 101

If a packet arrives on a router with the traffic class called cisco1 configured on the interface, the packet is evaluated to determine if it matches the IP protocol, QoS group 4, and access group 101. If all three of these match criteria are met, the packet is classified as a member of the traffic class cisco1.

The following example shows a traffic class that is configured with the class-map match-any command:

Router(config)# class-map match-any cisco2
Router(config-cmap)# match protocol ip
Router(config-cmap)# match qos-group 4
Router(config-cmap)# match access-group 101

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

Note that the class-map match-allcommand requires that all of the match criteria be met in order for the packet to be considered a member of the specified traffic class (a logical AND operator). In the first example, protocol IP AND QoS group 4 AND access group 101 must be successful match criteria. However, only one match criterion must be met in order for the packet in the class-map match-any command to be classified as a member of the traffic class (a logical OR operator). In the second example, protocol IP OR QoS group 4 OR access group 101 must be successful match criterion.

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 simply easier than retyping the same traffic class configuration. The more common reason for the match class-map command is to allow users to use match-any and match-all statements in the same traffic class. If you want to combine match-all and match-any characteristics in a traffic policy, create a traffic class using one match criterion evaluation instruction (either match-any or match-all) and then use this traffic class as a match criterion in a traffic class that uses a different match criterion type.

Here is a possible scenario: Suppose A, B, C, and D were all separate match criterion, and you wanted traffic matching for A, orB, or C and D (A or B or [C and D]) to be classified as belonging to the 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, and you would therefore 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 would also be A or B or [C and D]). The desired traffic class configuration has been achieved.

The only method of mixing match-all and match-any statements in a traffic class is through the use of the traffic class match criterion.

A traffic policy can be included in a QoS policy when the service-policy command is used in policy-map class configuration mode. A traffic policy that contains a traffic policy is called a hierarchical traffic policy.

A hierarchical traffic policy contains a child policy and a parent policy. The child policy is the previously defined traffic policy that is being associated with the new traffic policy through the use of the service-policy command. The new traffic policy using the preexisting traffic policy is the parent policy. In the example in this section, the traffic policy called child is the child policy and traffic policy called parent is the parent policy.

Hierarchical traffic policies can be attached to subinterfaces and ATM PVCs. When hierarchical traffic policies are used, a single traffic policy (with a child and a parent policy) can be used to shape and prioritize PVC traffic. In the following example, the child policy is responsible for prioritizing traffic and the parent policy is responsible for shaping traffic. In this configuration, the parent policy allows packets to be sent from the interface, and the child policy determines the order in which the packets are sent.

Router(config)# policy-map child
Router(config-pmap)# class voice
Router(config-pmap-c)# priority 50
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

The value used with the shape command is provisioned from the committed information rate (CIR) value from the service provider.