Quality of Service (QoS): Managing Bandwidth More Effectively

Preparation for Configuring QoS

Planning a QoS Configuration

QoS uses resources in a way that requires attention to rule usage when planning a QoS configuration. Otherwise, there is an increased possibility of oversubscribing resources, which means that at some point the switch would not support further QoS configuration.

Prioritizing and Monitoring QoS Configuration Options

Plan and implement your QoS configuration in descending order of feature importance. This helps to ensure that the most important features are configured first. Also, if insufficient rule resources become a problem, this approach can help you recognize how to distribute the desired feature implementations across multiple switches to achieve your objectives. For example, a given type of traffic may be of higher importance than other traffic types you want to expedite by using QoS. In this case you should plan and configure your QoS resource usage first for the most important traffic type before configuring QoS resource usage for other traffic types. If insufficient resources remain for all of the QoS implementation you want, try spreading this implementation across multiple switches.

Policy Enforcement Engine

The Policy Enforcement engine is the hardware element in the switch that manages quality-of-service and ACL policies, as well as other software fea­ tures, using the rules that you configure. Resource usage in the Policy Enforce­ ment engine is based on how these features are configured on the switch. For the switches covered in this guide, the term “resources” refers to the Policy Enforcement Engine resources available to that feature.

QoS Resource Usage and Monitoring

QoS configurations on the switches covered in this guide use rule resources as shown in Table 6-8. (How many resources are actually available depends on ACL usage as well.)

Table 6-8. QoS Rule Resource Usage

QoS Classifier

Rules Used

 

 

TCP and UDP Qos

2 per TCP or UDP Application

Device Priority QoS

2 per IP Address

ToS IP-Precedence

8 rules total per switch if this feature is enabled

QoS

 

6-15