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Early Inter-Domain Routing: The Exterior Gateway Protocol (EGP)

《TCP IP路由技术(第2卷)(第2版)英文版》本书是有关Cisco外部路由协议和高级IP路由主题的权威指南,是Cisco路由与交换领域实属罕见的经典著作。本书在上一版的基础上进行了全面更新,其可读性、广度和深度相较于上一版有了相当大的改进。本节为大家介绍Early Inter-Domain Routing: The Exterior Gateway Protocol (EGP)。

作者:【美】Jeff Doyle(杰夫 多伊尔)来源:人民邮电出版社|2017-11-05 18:07

Chapter 1 Inter-Domain Routing Concepts

Imagine what today’s Internet would be like if the whole thing was routed by a single routing protocol such as OSPF or IS-IS. The visibility of every subnet address would make stability almost impossible. Security would be a nightmare because an attack against the routing protocol—or even an innocent confi guration error—could bring down the entire Internet. And who would administer it? How would we coordinate an upgrade or enhancement of the protocol among all the network administrators around the world?

As the ARPANET , the precursor to the modern Internet, began growing large in the late 1970s, these issues were quite real, and efforts were begun to create a scalable way to manage the network. The fundamental concepts that arose from this work were the ideas of administrative domains called autonomous systems (AS), which defi ne the boundaries of networks under a common administration, and a protocol that could route among these domains: a routing protocol that is exterior to the administrative domains.

The protocol now used for routing among autonomous systems is the Border Gateway Protocol (BGP). Chapters 2 through 6 describe the function, confi guration, and troubleshooting of BGP and its associated routing policies. But before going there, this fi rst chapter introduces you to the key concepts behind BGP and how they evolved. Said differently, Chapters 2 through 6 give you the how whereas this chapter gives you the what and the why.

Early Inter-Domain Routing: The Exterior Gateway Protocol (EGP)

The first edition of this book committed its entire first chapter to examining the Exterior Gateway Protocol (EGP), the precursor to BGP. Even at that time, the protocol was almost obsolete and was used only in a few quite old networks. In the intervening years, the protocol has completed its slide into obsolescence and is no longer supported in IOS.

Yet EGP still offers insights into the first steps made toward a workable inter-domain (or inter-AS) routing protocol. This section, then, takes a look at EGP as a technical history lesson to help you better understand the lessons learned from it that guided the development of BGP. You can skip this section if you like, but several essential concepts introduced here carry over to BGP, and several functions help you understand some of the concepts behind BGP’s design.


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