Routing Flooding, Link-State EE122 Section 4

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

Flooding NOT a Spanning Tree A  G B A C D 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

Flooding Spanning Tree A  G B A C D 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

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

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

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

Learning Switch NO NEED TO FLOOD! 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!

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

Learning Switch Q1d) 1 1 1 3 1 Node A Node B Node C Node D Port A B C   Port A B C D E F G   Port A B C D E F G   Port A B C D E F G   Port A B C D E F G 1 1 1 3 1 Node A Node B Node C Node D

Learning Switch Q1d) 1 1 1 2 Node E Node F Node G Port A B C D E F G   Port A B C D E F G   Port A B C D E F G   Port A B C D E F G 1 1 1 2 Node E Node F Node G

Link-State Routing A C B D

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

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

Link-State Routing A B C D 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

Link-State Routing A B C D 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 20 C 8 4 D