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WAN Availability and QoS

Chapter Description

In this sample chapter from CCNP Enterprise Design ENSLD 300-420 Official Cert Guide: Designing Cisco Enterprise Networks, you will review WAN methodologies and WAN availability with deployment models using MPLS, hybrid, and Internet designs. It also covers backup connectivity, failover designs, QoS strategies, and designing end-to-end QoS policies.

This chapter covers the following subjects:

  • WAN Design Methodologies: This section discusses the processes of identifying business and technology strategies, assessing the existing network, and creating a design that is scalable, flexible, and resilient.

  • Design for High Availability: This section covers removing the single points of failure from a network design by using software features or hardware-based resiliency.

  • Internet Connectivity: This section discusses public network access and securely connecting business locations.

  • Backup Connectivity: This section discusses providing an alternative WAN path between locations when primary paths are unavailable.

  • QoS Strategies: This section discusses design models for providing QoS service differentiation.

  • Designing End-to-End QoS Policies: This section discusses options for QoS mechanisms such as queuing, policing, and traffic shaping.

This chapter covers WAN design and QoS. Expect plenty of questions on the ENSLD 300-420 exam about the selection and use of WAN designs in enterprise networks. A CCNP enterprise designer must understand WAN availability and the QoS models that are available to protect traffic flows in the network. This chapter starts with WAN methodologies and then covers WAN availability with deployment models using MPLS, hybrid, and Internet designs. This chapter also explores backup connectivity and failover designs. Finally, it covers QoS strategies and designing end-to-end QoS policies.

“Do I Know This Already?” Quiz

The “Do I Know This Already?” quiz helps you identify your strengths and deficiencies in this chapter’s topics. This quiz, derived from the major sections in the “Foundation Topics” portion of the chapter, helps you determine how to spend your limited study time. Table 9-1 outlines the major topics discussed in this chapter and the “Do I Know This Already?” quiz questions that correspond to those topics. You can find the answers in Appendix A, “Answers to the ‘Do I Know This Already?’ Quiz Questions Q&A Questions.”

Table 9-1 “Do I Know This Already?” Foundation Topics Section-to-Question Mapping

Foundation Topics Section

Questions Covered in This Section

WAN Design Methodologies


Design for High Availability


Internet Connectivity


Backup Connectivity


QoS Strategies


Designing End-to-End QoS Policies


1. Which of the following is a measure of data transferred from one host to another in a given amount of time?

  1. Reliability

  2. Response time

  3. Throughput

  4. Jitter

2. Which of the following is a description of the key design principle scalability?

  1. Modularity with additional devices, services, and technologies

  2. Redundancy through hardware, software, and connectivity

  3. Ease of managing and maintaining the infrastructure

  4. Providing enough capacity and bandwidth for applications

3. What percentage of availability allows for four hours of downtime in a year?

  1. 99.5%

  2. 99.99%

  3. 99.999%

  4. 99.95%

4. What Internet connectivity option provides the highest level of resiliency for services?

  1. Single-router dual-homed

  2. Single-router single-homed

  3. Dual-router dual-homed

  4. Shared DMZ

5. Which of the following eliminates single points of failures with the router and the circuit?

  1. Dual-router dual-homed

  2. Single-router dual-homed

  3. Shared DMZ

  4. Single-router single-homed

6. What backup option allows for both a backup link and load-sharing capabilities using the available bandwidth?

  1. Dial backup

  2. Secondary WAN link

  3. IPsec tunnel

  4. GRE tunnel

7. Which of the following adds a strict priority queue to modular class-based QoS?

  1. FIFO

  2. CBWFQ

  3. WFQ

  4. LLQ

8. Which of the following is a mechanism to handle traffic overflow using a queuing algorithm with QoS?

  1. Congestion management

  2. Traffic shaping and policing

  3. Classification

  4. Link efficiency

9. Which QoS model uses Resource Reservation Protocol (RSVP) to explicitly request QoS for the application along the end-to-end path through devices in the network?

  1. DiffServ

  2. IntServ

  3. CBWFQ

  4. BE

10. What technique does traffic shaping use to release the packets into the output queue at a preconfigured rate?

  1. Token bucket

  2. Leaky bucket

  3. Tagging

  4. Interleaving

Foundation Topics

This chapter describes the WAN design and QoS topics you need to master for the ENSLD 300-420 exam. These topics include WAN methodologies in the enterprise edge, WAN availability, and WAN designs including backup and failover options. In addition, this chapter describes quality of service (QoS) and how it can be used to prioritize network traffic and better utilize the available WAN bandwidth.

2. WAN Design Methodologies | Next Section

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