Learning Objectives

After successfully completing this section, you should be able to

  1. explain why inter-autonomous system routing is needed.
  2. explain how routing is done between autonomous systems.
  3. explain what BGP is, what it does, and how.

Learning Tasks

Required:

  1. Watch the slideshow for this section.
  2. Study Section 5.4, Routing Among the ISPs: BGP, in the textbook.

Terms and Topics

Section 4 – Routing Among the ISPs: BGP

Border router
Border gateway protocol (BGP)
BGP for inter-AS routing
BGP functionalities
External BGP (eBGP) session
Internal BGP (iBGP) session
BGP peers
Path attributes in BGP

BGP routes
Autonomous system numbering (ASN) in BGP
BGP route selection
BGP routing policy
Hot potato routing

Leading Questions

  1. How are packets routed from one AS to another?
  2. What is the border gateway protocol (BGP) used for?
  3. In inter-AS routing, what information does a border gateway routing protocol need to provide to a router?
  4. What is the best route between autonomous systems?
  5. What are the four types of messages defined by BGP?
  6. What are the differences between IBGP and EBGP?
  7. Why are there different inter-AS and intra-AS routing protocols?
  8. What is a global routing algorithm for a network?
  9. Why is a global routing algorithm referred to as a link-state algorithm?
  10. What are the differences between distance-vector algorithms and link-state algorithms?
  11. How are link cost changes and link failures handled in the distance-vector algorithm?
  12. What is hot potato routing?
  13. How does BGP select a route?
  14. What is head of line (HOL) blocking?
  15. What was the main initiative for the IETF to develop Internet protocol version 6 (IPv6)?
  16. What packet format is used by IPv6? What are the main changes compared to IPv4?
  17. What is IP-anycast?
  18. What is an anycast address?