In preparation of your CCNP exam, we want to make sure we cover the various concepts that we could see on your Cisco CCNP exam. So to assist you, below we will discuss on of the more difficult CCNP concepts; Low Latency Queueing. As you progress through your CCNP exam studies, I am sure with repetition you will find this topic becomes easier. So even though it may be a difficult concept and confusing at first, keep at it as no one said getting your Cisco certification would be easy!

Introduction

This sample configuration illustrates the Low Latency Queueing feature. The Low Latency Queueing feature brings strict priority queueing to Class-Based Weighted Fair Queueing (CBWFQ). Configured by the priority command, strict priority queueing gives delay-sensitive data, such as voice, preferential treatment over other traffic. With this feature, delay-sensitive data is sent first (before packets in other queues are treated). Low Latency Queueing documentation provides additional details about this feature.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

Low Latency Queueing has been supported on all platforms running Cisco IOS® Software release12.0(7)T and later. For further information on this, refer to Supported Platforms.

For Cisco 7500 routers, Low Latency Queueing is supported in Cisco IOS Software release 12.0.(7)XE and later. For more information, refer to Supported Platforms.

For an overview of feature evolution on Cisco IOS Software releases, refer to Feature Overview.

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Conventions

For more information on document conventions, refer to Cisco Technical Tips Conventions.

Configure

In this section, you are presented with the information to configure the features described in this document.

Note: To find additional information on the commands used in this document, use the Command Lookup Tool ( registered customers only) .

Network Diagram

This document uses this network setup:

Note: In this configuration:

• The Cisco 7200s 2 and 4 are equipped with a PA-A3 and configured with the CBWFQ Low Latency Queueing feature.
• A policy-map statement is configured to classify the packets originating from Router 1, 10.2.2.2, and directed to 10.6.6.2 (device connected to Router 4). Low Latency Queueing is configured to give priority to this flow and allocate 70K of the 100K SCR vbr-nrt PVC configured between the two routers.
• A ping traffic simulates the constant traffic flow between Source 10.2.2.2 and Destination 10.6.6.2. A ping traffic with timeout 0 generated from Router 3 towards 10.5.5.10 connected to Router 4 will simulate the congesting flow.
• The queue-limit keyword under class-default is used to limit the queue depth of the congesting traffic.
• The tx-ring-limit command is used to reduce the PA First In, First Out (FIFO) queue.
• The show queue atm2/0.1 command shows the null weight assigned to the high priority flow. Any packet matching that flow is immediately scheduled for transmission. Packets assigned to the default class are queued up to the maximum queue-limit threshold and dropped if the congestion state persists.

Configurations

This document uses these configurations:

• Cisco 7200 Router 2
• Cisco 7200 Router 4

Verify

This section provides information you can use to confirm your configuration is working properly.

Certain show commands are supported by the Output Interpreter Tool ( registered customers only) , which allows you to view an analysis of show command output.

• show queueLists fair queueing configuration and statistics for a particular interface.
• show policy-map interfaceDisplays the configuration of all classes configured for all service policies on the specified interface.

I hope you found this article to be of use and it helps you prepare for your Cisco CCNP certification. Achieving your CCNP certification is much more than just memorizing Cisco exam material. It is having the real world knowledge to configure your Cisco equipment and be able to methodically troubleshoot Cisco issues. So I encourage you to continue in your studies for your CCNP exam certification.