What is CBQoS?

CBQoS (Class-Based Quality of Service) is a Cisco feature set that is part of the IOS 12.4(4)T and above. This data is retrieved using SNMP and provides information on the QoS policies applied and class-based traffic patterns within an enterprise's network.

Why do I need CBQoS ?

Typically, networks operate on the basis of best-effort delivery, in which all traffic has equal priority and an equal chance of being delivered. When congestion results, all traffic has an equal chance of being dropped. QoS selects network traffic, prioritizes it according to its relative importance, and uses congestion avoidance to provide priority-indexed treatment. CBQoS can also limit the bandwidth used by network traffic. CBQoS can make network performance more predictable and bandwidth utilization more effective. Network administrators implement CBQoS policies to ensure that their business-critical applications receive the highest priority on the network. CBQoS provides you in depth visibility into the policies applied on your links and the traffic patterns in your various class of traffic. The pre-policy, post-policy and drops in different traffic class along with the queuing status enables you to validate the efficiency of your QoS settings.

• Creating a traffic class
• Creating a traffic policy
• Attaching a Traffic Policy to an Interface
• Verifying the Traffic Class and Traffic Policy Information

How do I start CBQoS data collection?

Configuring Policies on the router

Initially, CBQoS has to be enabled on the router manually. Further, policies have to be defined on the router. Usually, Traffic Policies are dependent on the type of enterprise and its business needs. ( heavy voice traffic, heavy document transfer, heavy streaming video traffic, etc ). The policy / classification can be done on the basis of Class Maps and Policy Maps.

A class map is a mechanism that you use to isolate and name a specific traffic flow (or class) from all other traffic. The class map defines the criterion used to match against a specific traffic flow to further classify it; the criteria can include matching the access group defined by the ACL or matching a specific list of DSCP or IP precedence values. If you have more than one type of traffic that you want to classify, you can create another class map and use a different name. After a packet is matched against the class-map criteria, you can specify the QoS actions via a policy map. A policy map specifies the QoS actions for the traffic classes. Actions can include trusting the CoS or DSCP values in the traffic class; setting a specific DSCP or IP precedence value in the traffic class; or specifying the traffic bandwidth limitations and the action to take when the traffic is out of profile. Before a policy map can be effective, you must attach it to an interface.

After a packet is classified and has an internal DSCP value assigned to it, the policing and marking process has to be done. Policing involves creating a policy that specifies the bandwidth limits for the traffic. Packets that exceed the limits are out of profile or nonconforming. Each policy specifies the action to take for packets that are in or out of profile. These actions, carried out by the marker, include passing through the packet without modification, dropping the packet, or marking down the packet with a new DSCP value that is obtained from the configurable policed-DSCP map.

Fetching Policy Details from The Router

The policy details from the router can be found under Settings>Netflow>CBQos, the CBQoS Configuration tab lists all the interfaces that have policies applied on them are displayed along with the router names and specific IN and OUT Policies. To facilitate the NetFlow Analyzer application to recognize the policies applied at each router level, click on the icon. This list all the routers, along with their Policies. By clicking on "Fetch Policy" it is possible to fetch the policy details from the router about each individual interface.

Once the policy details have been fetched from the routers the following message is displayed: "Policy Details Updated". If any policy is not found the "Not Available" message is displayed.

Polling for CBQoS data

After setting the policies on the router and fetching the policy details polling can be started. Click on the "Update Polling" button to select/unselect the interfaces on which polling has to be done. The Polling Parameters namely Polling Interval and Time Out can also be modified. The Polling interval can take any value from 5, 10, 15, 25, 30, 60. Time Out can take values from 5, 10, 15. After selecting/deselecting the list of interfaces on which Polling has to be done and after the Polling Parameters have been set click on "Update Polling" to start the polling action.

Creating a traffic class

To create a traffic class, use the class-map command. The syntax of the class-map command is as follows:

class-map [match-any | match-all] class-name
no class-map [match-any | match-all] class-name

• The match-all and match-any Keywords
• The match-all and match-any keywords need to be specified only if more than one match criterion is configured in the traffic class.
• The match-all keyword is used when all of the match criteria in the traffic class must be met in order for a packet to be placed in the specified traffic class.
• The match-any keyword is used when only one of the match criterion in the traffic class must be met in order for a packet to be placed in the specified traffic class.
• If neither the match-all nor match-any keyword is specified, the traffic class will behave in a manner consistent with the match-all keyword.

About The match not Command

The match not command, rather than identifying the specific match parameter to use as a match criterion, is used to specify a match criterion that prevents a packet from being classified as a member of the class. For instance, if the match not QoS-group 6 command is issued while you configure the traffic class, QoS group 6 becomes the only QoS group value that is not considered a successful match criterion. All other QoS group values would be successful match criteria.

Procedure

To create a traffic class containing match criteria, use the class-map command to specify the traffic class name. Then use one or more match commands to specify the appropriate match criteria. Packets matching the criteria you specify are placed in the traffic class.

Creating a traffic policy

To configure a traffic policy (sometimes also referred to as a policy map), use the policy-map command. The policy-map command allows you to specify the traffic policy name and also allows you to enter policy-map configuration mode (a prerequisite for enabling QoS features such as traffic policing or traffic shaping).

Associate the Traffic Policy with the Traffic Class

After using the policy-map command, use the class command to associate the traffic class (created in the "Creating a Traffic Class" section) with the traffic policy.

The syntax of the class command is as follows:

class class-name
no class class-name

For the class-name argument, use the name of the class you created when you used the class-map command to create the traffic class (Step 3 of the "Creating a Traffic Class" section).

After entering the class command, you are automatically in policy-map class configuration mode. The policy-map class configuration mode is the mode used for enabling the specific QoS features.

Procedure

To create a traffic policy (or policy map) and enable one or more QoS features, perform the following steps.

Configuration Steps

Attaching a Traffic Policy to an Interface

To attach a traffic policy to an interface, use the service-policy command. The service-policy command also allows you to specify the direction in which the traffic policy should be applied (either on packets coming into the interface or packets leaving the interface).

The service-policy command syntax is as follows:

service-policy {input | output} policy-map-name
no service-policy {input | output} policy-map-name

Procedure

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

Verifying the Traffic Class and Traffic Policy Information

To display and verify the information about a traffic class or traffic policy, perform the following steps.

Using the CBQoS data

Once Polling has been started, reports can be viewed under the CBQoS tab. Reporting is available in terms of Volume of Traffic, Number of Packets, Traffic Speed and Queue. The pre-policy, post-policy and drops in different traffic class along with the queuing status enables you to validate the efficiency of your QoS settings. Individual graphs are displayed for Pre Policy, Post Policy and Dropped. Pre Policy refers to the state before the CBQoS policy was applied. Post Policy refers to the state after the CBQoS policy is applied. Dropped gives information on the packets that are dropped as a result of applying the policies.

CBQoS reports can be exported as PDF or can be mailed by going to "Actions" and clicking on the necessary action.

Based on these information suitable corrections can be done to the policies to make it best suit the business goals of the organization.