Enhanced Interior Gateway Routing Protocol (EIGRP)

This chapter covers the following topics:

• EIGRP Fundamentals: This section explains how EIGRP establishes a neighborship with other routers and how routes are exchanged with other routers.

• EIGRP Configuration Modes: This section defines the two methods of configuring EIGRP with a baseline configuration.

• Path Metric Calculation: This section explains how EIGRP calculates the path metric to identify the best and alternate loop-free paths.

Enhanced Interior Gateway Routing Protocol (EIGRP) is an enhanced distance vector routing protocol commonly found in enterprise networks. EIGRP is a derivative of Interior Gateway Routing Protocol (IGRP) but includes support for variable-length subnet masking (VLSM) and metrics capable of supporting higher-speed interfaces. Initially, EIGRP was a Cisco proprietary protocol, but it was released to the Internet Engineering Task Force (IETF) through RFC 7868, which was ratified in May 2016.

This chapter explains the underlying mechanics of the EIGRP routing protocol and the path metric calculations, and it demonstrates how to configure EIGRP on a router. This is the first of several chapters in the book that discuss EIGRP:

• Chapter 2, “EIGRP”: This chapter describes the fundamental concepts of EIGRP.

• Chapter 3, “Advanced EIGRP”: This chapter describes EIGRP’s failure detection mechanisms and techniques to optimize the operations of the routing protocol. It also includes topics such as route filtering and traffic manipulation.

• Chapter 4, “Troubleshooting EIGRP for IPv4”: This chapter reviews common problems with the routing protocols and the methodology to troubleshoot EIGRP from an IPv4 perspective.

• Chapter 5, “EIGRPv6”: This chapter demonstrates how IPv4 EIGRP concepts carry over to IPv6 and the methods used to troubleshoot common problems.

“Do I Know This Already?” Quiz

The “Do I Know This Already?” quiz allows you to assess whether you should read this entire chapter thoroughly or jump to the “Exam Preparation Tasks” section. If you are in doubt about your answers to these questions or your own assessment of your knowledge of the topics, read the entire chapter. Table 2-1 lists the major headings in this chapter and their corresponding “Do I Know This Already?” quiz questions. You can find the answers in Appendix A, “Answers to the ‘Do I Know This Already?’ Quiz Questions.”

Table 2-1 “Do I Know This Already?” Foundation Topics Section-to-Question Mapping

1. EIGRP uses protocol number ____ for inter-router communication.

   1. 87

   2. 88

   3. 89

   4. 90

2. How many packet types does EIGRP use for inter-router communication?

   1. Three

   2. Four

   3. Five

   4. Six

   5. Seven

3. Which of the following are not required to match in order to form an EIGRP adjacency?

   1. Metric K values

   2. Primary subnet

   3. Hello and hold timers

   4. Authentication parameters

4. What is an EIGRP successor?

   1. The next-hop router for the path with the lowest path metric for a destination prefix

   2. The path with the lowest metric for a destination prefix

   3. The router selected to maintain the EIGRP adjacencies for a broadcast network

   4. A route that satisfies the feasibility condition where the reported distance is less than the feasible distance

5. What attributes does the EIGRP topology table contain? (Choose all that apply.)

   1. Destination network prefix

   2. Hop count

   3. Total path delay

   4. Maximum path bandwidth

   5. List of EIGRP neighbors

6. What destination addresses does EIGRP use when feasible? (Choose two.)

   1. IP address 224.0.0.9

   2. IP address 224.0.0.10

   3. IP address 224.0.0.8

   4. MAC address 01:00:5E:00:00:0A

   5. MAC address 0C:15:C0:00:00:01

7. Which of the following techniques can be used to initialize the EIGRP process? (Choose two.)

   1. Use the interface command ip eigrp as-number ipv4 unicast.

   2. Use the global configuration command router eigrp as-number.

   3. Use the global configuration command router eigrp process-name.

   4. Use the interface command router eigrp as-number.

8. True or false: The EIGRP router ID (RID) must be configured for EIGRP to be able to establish neighborship.

   1. True

   2. False

9. True or false: When using MD5 authentication between EIGRP routers, the keychain sequence numbers used on the routers can be different, as long as the password is the same.

   1. True

   2. False

10. Which value can be modified on a router to manipulate the path taken by EIGRP but does not have an impact on other routing protocols, like OSPF?

    1. Interface bandwidth

    2. Interface MTU

    3. Interface delay

    4. Interface priority