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Introduction to BGP

Chapter Description

In this sample chapter from Routing TCP/IP, Volume II: CCIE Professional Development, 2nd Edition, author Jeff Doyle covers the basic operation of BGP, including its message types, how the messages are used, and the format of the messages. You also learn about the various basic attributes BGP can associate with a route and how it uses these attributes to choose a best path. Finally, this chapter shows you how to configure and troubleshoot BGP peering sessions.

Review Questions

  1. vWhat is an untrusted administrative domain, and why is it untrusted?

  2. In what way does BGP require you to think differently about peering than an IGP does?

  3. What AS numbers are reserved for private use?

  4. What are the four BGP message types, and how is each one used?

  5. What happens if two BGP neighbors advertise different hold times in their Open messages?

  6. What does a negotiated hold time of 0 indicate?

  7. What is the IOS default period for sending BGP Keepalive messages?

  8. What is the BGP identifier, and how is it selected?

  9. In what state or states can BGP peers exchange Update messages?

  10. What is NLRI?

  11. What is a path attribute?

  12. What is a Withdrawn route?

  13. What happens when a BGP Notification message is received?

  14. What is the difference between the Connect state and the Active state?

  15. What causes a transition to the OpenConfirm state, and what are the next steps when the BGP process shows a neighbor in this state?

  16. What are the four categories of BGP path attributes?

  17. What does well-known mandatory mean, and what are the three well-known mandatory path attributes?

  18. What is the purpose of the ORIGIN attribute?

  19. What is the purpose of the AS_PATH attribute?

  20. When does a router add its AS number to the AS_PATH list of an Update?

  21. What is AS path prepending?

  22. What are AS_SEQUENCE and AS_SET, and what is the difference between them?

  23. What is the purpose of the NEXT_HOP attribute?

  24. What is a recursive route lookup, and why is it important to BGP?

  25. What happens if a router receives a BGP route with a NEXT_HOP address that is unknown to the router?

  26. What are the three parts of a BGP routing information database (RIB), and what is the function of each?

  27. What do all the NLRI in a BGP Update message have in common?

  28. Does BGP require a TCP connection between IPv6 addresses to advertise IPv6 prefixes?

  29. What is the IOS default TTL value of BGP message packets sent to external peers?

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