Chapter 1. Exterior Gateway Protocol

This chapter covers the following key topics:

• The Origins of EGP ” This section discusses the history of the development of the Exterior Gateway Protocol, presented in RFC 827 (1982).

• Operation of EGP ” This section explores the fundamental mechanics of EGP with a focus on EGP topology issues, EGP functions, and EGP message formats.

• Shortcomings of EGP ” This section explores some of the reasons why EGP is no longer pursued as a viable external gateway protocol solution.

• Configuring EGP ” This section presents four separate case studies ”EGP stub gateway, EGP core gateway, indirect neighbors, and default routes ”to demonstrate different types of EGP configuration.

• Troubleshooting EGP ” This section examines how to interpret an EGP neighbor table and presents a case study on the slow convergence speed of an EGP network to show why EGP is no longer a popular option.

The first question knowledgeable readers will (and should) ask is "Why kill a few trees publishing a chapter about an obsolete protocol such as the Exterior Gateway Protocol (EGP)?" After all, EGP has been almost universally replaced by the Border Gateway Protocol (BGP). This question has two answers.

First, although EGP is rarely used these days, it is still occasionally encountered . As of this writing, for instance, you can still find EGP in a few U.S. military internetworks. As a CCIE, you should understand EGP for such rare encounters.

Second, this chapter serves as something of a history lesson. Examining the motives for developing an external gateway protocol and the shortcomings of the original external protocol provides a prologue for the following two chapters. BGP will make more sense to you if you are familiar with the roots from which it evolved.