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Routing

Routing. Flooding, Link-State. EE122 Section 4. First off, where are we?. Application. Transport. Mostly still here. Network. Datalink. Physical. Flooding. B. A. C. D. A  G. E. G. F. Does every node receive A’s packet? Does every node receive exactly one copy of A’s packet?

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Routing

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  1. Routing Flooding, Link-State EE122 Section 4

  2. First off, where are we? Application Transport Mostly still here Network Datalink Physical

  3. Flooding B A C D A  G E G F Does every node receive A’s packet? Does every node receive exactly one copy of A’s packet? (i.e. is there exactly one way to reach every node?) NOT a Spanning Tree

  4. Flooding B A C D A  G E G F Does every node receive A’s packet? Does every node receive exactly one copy of A’s packet? (i.e. is there exactly one way to reach every node?) Spanning Tree

  5. Spanning Tree Rooted at G B A C D E G F Every node can reach G by following the arrows

  6. Spanning Tree Rooted at E B A C D E G F Every node can reach E by following the arrows

  7. Spanning Tree • Loop-free, dead-end-free topology • Easiest way to reach destination is Flooding B A C D E G F • Wasteful  Motivation for Learning Switch

  8. Learning Switch • Q1a) Node A wants to reach Node G • All nodes now know which • port to reach Node A on • Packet takes the path A – E – F – G • Q1b) Node F wants to reach Node A • Node F knows Node A is • on its left port • Node E knows Node A is • on its upper port • Packet takes the path F– E – A B A C D E G F NO NEED TO FLOOD!

  9. Learning Switch • Q1c) Node B wants to reach Node F • Flood or no? • When do we stop? • Nodes ACEF receive the packet • Packet takes the path B-A-E-F B A C D E G F

  10. Learning Switch Q1d) 1 1 1 1 3 1 Node A Node B Node C Node D

  11. Learning Switch Q1d) 1 1 1 1 1 2 Node E Node F Node G

  12. Link-State Routing A B C D

  13. Link-State Routing Q2a) A (1, A) (5, A) ∞ (1, A) (3, B) (9, B) 1 5 (1, A) (3, B) (7, C) B 2 C Node A 8 4 (1, B) (2, B) (8, B) D (2, B) (8, B) (1, B) (1, B) (2, B) (6, C) Node B

  14. Link-State Routing Q2a) A (5, C) (2, C) (4, C) (3, B) (2, C) (4, C) 1 5 (3, B) (2, C) (4, C) B 2 C Node C 8 4 ∞ (8, D) (4, D) D (6, C) (4, D) (9, C) (7, B) (6, C) (4, D) Node D

  15. Link-State Routing • Q2b) Node A sends to D • Shortest path: ABCD • Cost: 7 • What if the nodes don’t have the same map? A 1 5 B 2 C 8 4 D

  16. Link-State Routing • Q2c) Cost of link BC = 20, B sends to C • B thinks shortest path is BAC • A thinks shortest path is ABC • B  A  B  A… • Cost: ∞ A 1 5 B C 20 8 4 D

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