Chapter 15. BGP Neighbors

This chapter covers the following topics:

  • Basic BGP Configuration Commands—Describes the commands for forming BGP neighbor relationships and advertising networks.

  • Managing and Verifying the BGP Configuration—Describes the common BGP commands used to view the status of BGP neighbor relationships and the routes learned through these relationships.

  • Resetting Neighbors—Describes the methods for resetting BGP neighbor relationships.

This chapter details the basic configuration of BGP: how to configure iBGP and eBGP neighbor relationships, how to advertise routes, and how to summarize routes. You also learn how to display the status of BGP neighbor relationships, the routes learned via BGP neighbor relationships, and how to reset BGP neighbor relationships. Once you master the content of this chapter, the remaining topics in BGP consist of advanced methods for performing policy routing.

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 15-1 outlines the major topics discussed in this chapter and the "Do I Know This Already?" quiz questions that correspond to those topics.

Table 15-1. "Do I Know This Already?" Foundation Topics Section-to-Question Mapping
Foundation Topics SectionQuestions Covered in This SectionScore
Basic BGP Configuration Commands1–6 
Managing and Verifying the BGP Configuration7–8 
Resetting Neighbors9–11 
Total Score  


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.What is the purpose of the network command?
  1. To advertise the stated network

  2. To identify the interfaces to run BGP

  3. To forward stated networks

  4. To create neighbors within these networks

2.What is the purpose of the neighbor command?
  1. Forces the path to be chosen

  2. Identifies the next hop router and sends LSAs and hellos

  3. States the address and autonomous system of the neighbor with whom to peer

  4. States the neighbor that might be considered as feasible paths

3.Which command enables the BGP process?
  1. router bgp remote autonomous-system-number

  2. router bgp process-id

  3. ip routing bgp

  4. router bgp autonomous-system-number

4.Which IP is used for the source address of BGP traffic in the absence of the command update-source?

  2. Derived from the AS

  3. Router ID

  4. Output interface

5.BGP next hop is (by default) set to which of the following?
  1. The first router in the AS

  2. Your BGP neighbor

  3. The first router in the advertising AS

  4. The local router

6.How can you tell which neighbors are iBGP?
  1. The remote AS is zero

  2. Check the list of local AS

  3. The local AS is the same as the remote AS

  4. show ip bgp neighbor

7.Which command is used to show the BGP connections between peers?
  1. show ip bgp connections

  2. show ip bgp neighbor

  3. show ip bgp sessions

  4. show ip bgp topology

8.Which command is used to show the number of prefixes learned from a BGP neighbor?
  1. show ip bgp connections

  2. show ip bgp sessions

  3. show ip bgp topology

  4. show ip bgp summary

9.What is the purpose of the command clear ip bgp *?
  1. To disconnect all sessions

  2. To clear the BGP routing table

  3. To end an administrative session

  4. To clear all IGP entries from the routing table

10.Which of the following techniques can be entered at both ends of a BGP connection to resend BGP updates so that routing policy may be reapplied?
  1. Rebooting the local router

  2. clear ip bgp *

  3. clear ip bgp * soft in

  4. clear ip bgp * soft out

11.Which technique allows policies to be reapplied without destroying the existing peering?
  1. Rebooting the local router

  2. clear ip bgp *

  3. clear ip bgp * soft in

  4. clear ip bgp * soft out

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," "Q&A," and "Scenarios" sections.

  • 8 or 9 overall score—Begin with the "Foundation Summary" section, and then go to the "Q&A" and "Scenarios" sections 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" and "Scenarios" sections. Otherwise, move on to the next chapter.