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Border Gateway Protocol: Policy-Based Routing in Inter-Domain Networks

Learn about BGP, a path vector protocol for inter-domain routing designed to enforce policies and privacy. Discover why distance-vector and link-state protocols may not suffice due to varying policies across domains. Explore route selection, export policies, and the dynamic relationships between providers, customers, and peers. Experience a BGP routing game simulation to understand route selection precedence in a network environment.

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Border Gateway Protocol: Policy-Based Routing in Inter-Domain Networks

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  1. BGP EE122 Discussion 11/7/11

  2. Border Gateway Protocol • Protocol for inter-domain routing • Designed for policy and privacy • Why not distance-vector? • Shortest path may not be policy-compliant • …and policies vary across domains! • Why not link-state? • Everybody knows everything – privacy goes for a toss! • Enter path vector!

  3. BGP: Path Vector 0 A: 1 B: 2 1 2 A: 1 B: 2 A B

  4. BGP: Path Vector 0 A: 0 1 B: 0 2 B: 0 2 A: 0 1 1 2 A: 1 B: 2 A B

  5. BGP: Path Vector 0 A: 0 1 B: 0 2 1 2 A: 1 B: 1 0 2 A: 2 0 1 B: 2 A B

  6. BGP: Path Vector 0 A: 0 1 B: 0 2 A: 0 1 B: 0 Withdrawal - B: 0 2 Advertise - B: 0 1 2 A: 1 B: 1 0 A: 2 0 1 B: 2 A B

  7. BGP Relationships • Provider -> Customer: • Peer <-> Peer: A: 1 0 B: 1 0 C: 0 0 A: 1 B: 1 C: 0 1 1 2 A: 1 2 B: 2 C: 0 2 A B C

  8. It’s all about the money! • Customer pays provider • Peers don’t pay each other • Assume equal flow both ways • Routing policies try to minimize payment

  9. Packets flow where money flows • Route Selection • Preference Order: Customer > Peer > Provider • Route Export Policy • Peers provide transit between their customers • Peers do not provide transit to each other

  10. Route Selection: Customer > Peer • Provider -> Customer: • Peer <-> Peer: A: 1 0 B: 1 0 C: 0 0 A: 1 B: 1 C: 0 1 1 2 A: 1 2 B: 2 C: 0 2 A B C

  11. Route Selection : Peer > Provider • Provider -> Customer: • Peer <-> Peer: A: 1 0 B: 1 0 C: 0 0 A: 1 B: 1 C: 0 1 1 2 A: 1 2 B: 2 C: 0 2 A B C

  12. Route Selection : Provider (no choice) • Provider -> Customer: • Peer <-> Peer: A: 1 0 B: 1 0 C: 0 0 A: 1 B: 1 C: 0 1 1 2 A: 1 2 B: 2 C: 0 2 A B C

  13. Packets flow where money flows • Route Selection • Preference Order: Customer > Peer > Provider • Route Export Policy • Peers provide transit between their customers • Peers do not provide transit to each other

  14. BGP Export policy: Advertise customers • Provider -> Customer: • Peer <-> Peer: A: 1 0 B: 1 0 C: 0 0 A: 1 B: 1 C: 0 1 1 2 A: 1 2 B: 2 C: 0 2 A B C

  15. BGP Routing Game! • No talking! Communicate via pieces of paper • Route selection precedence • Customer > Peer > Provider • Export policy: Advertise customers • Message format: • Withdrawal - <host network>: <path> • Advertise - <host network>: <path> • Goal: Reach steady state

  16. BGP Game Steady State A: 0 B: 3 0 C: 4 2 0 A: 0 2 B: 3 1 2 C: 4 2 2 1 0 A: 0 1 B: 3 1 C: 4 2 1 3 A: 0 3 B: 3 C: 4 3 4 A: 0 2 4 B: 3 4 C: 4 A B C

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