Chapter 14. BGP Concepts

This chapter covers the following topics:

Introduction to BGP—Describes where and when to use BGP, as well as some basic BGP operations.
Connecting to the Internet with BGP—Describes multihoming and load sharing.
Synchronization—Describes what synchronization is and when to use it.
BGP States—Describes the five neighbor states for BGP.

This chapter details Border Gateway Protocol version 4 (BGP-4, referred to throughout this book as BGP). This chapter deals with the basic concepts and configuration commands of BGP, which are covered in greater complexity in Chapter 15, "BGP Neighbors." This chapter builds on your understanding of routing within large enterprise networks. This chapter introduces external BGP (eBGP) and familiarizes you with the necessary terms and concepts.

This chapter deals with how BGP works theoretically. Implementing and managing a BGP network is described in Chapter 15.

The purpose of the "Do I Know This Already?" quiz is to help you decide what parts of this chapter to use. If you already intend to read the entire chapter, you do not necessarily need to answer these questions now.

The 11-question 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 14-1 outlines the major topics discussed in this chapter and the "Do I Know This Already?" quiz questions that correspond to those topics.

Table 14-1. "Do I Know This Already?" Foundation Topics Section-to-Question Mapping
Foundation Topics Section	Questions Covered in This Section	Score
Introduction to BGP	1–5
Connecting to the Internet with BGP	6–7
Synchronization	8–9
BGP States	10–11
Total Score

Caution

The goal of self-assessment is to gauge your mastery of the topics in this chapter. If you do not know the answer to a question or are only partially sure of the answer, you should mark this question wrong for purposes of the self-assessment. Giving yourself credit for an answer you correctly guess skews your self-assessment results and might provide you with a false sense of security.

1.	Which of the following are key features of BGP? Periodic keepalives Periodic updates Poison reverse Triggered updates
2.	Which of the following best describes the routers that utilize eBGP to communicate with each other? Routers within an autonomous system Routers in different countries Routers in different autonomous systems Routers running different IGPs
3.	What is the transport protocol for BGP? BGP runs directly on top of the data link layer IP UDP TCP
4.	When are full routing updates sent in BGP? At the beginning of each established session Whenever a fault is seen on the link Every 30 minutes At the startup of the BGP process

5.	Which of the following are BGP message types? Updates Keepalives ACK Notification
6.	Place the BGP connection strategies in order from lowest to highest, in terms of memory and bandwidth requirements. Accept only default routes from all providers Accept some routes plus a default route from all providers Accept full routing updates from all providers
7.	Place the BGP connection strategies in order from lowest to highest, in terms of likelihood to take the best path. Accept only default routes from all providers Accept some routes plus a default route from all providers Accept full routing updates from all providers
8.	The synchronization rule is best described by which of the following? Do not use or advertise a route until the route is learned from a BGP peer. Wait until a CONFIRM message is received before using routes from BGP neighbors. Do not use or internally advertise a route until the route is learned from a source other than BGP. Do not use or advertise routes marked PARTIAL.
9.	Which of the following are benefits of enabling BGP synchronization? It prevents traffic from being forwarded to unreachable destinations. It reduces unnecessary traffic. It ensures consistency within the autonomous system. It ensures access to a complete set of Internet routes.

10.	Place the BGP states in order, from startup to peering. Open Sent Idle Established Open Confirm Connect
11.	Ideally, the output of the show ip bgp neighbors command will display what? Open Active Established Idle

The answers to the "Do I Know This Already?" quiz are found in Appendix A, "Answers to Chapter 'Do I Know This Already?' Quizzes and Q&A Sections." The suggested choices for your next step are as follows:

7 or less overall score—Read the entire chapter. This includes the "Foundation Topics," "Foundation Summary," and "Q&A" sections.
8 or 9 overall score—Begin with the "Foundation Summary" section, and then go to the "Q&A" section at the end of the chapter. If you have trouble with these exercises, read the appropriate sections in "Foundation Topics."
10 or 11 overall score—If you want more review on these topics, skip to the "Foundation Summary" section, and then go to the "Q&A" section. Otherwise, move on to the next chapter.