Routing Flooding LinkState EE 122 Section 4 First

Routing Flooding, Link-State EE 122 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? (i. e. is there exactly one way to reach every node? ) NOT a Spanning Tree

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

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-endfree topology A B C D • Easiest way to reach destination is Flooding E F G • Wasteful Motivation for Learning Switch

Learning Switch A Q 1 a) Node A wants to reach Node G B C D All nodes now know which port to reach Node A on Packet takes the path A – E – F – G E F G Q 1 b) Node F wants to reach Node A Node F knows Node A is on its left port NO NEED TO FLOOD! Node E knows Node A is on its upper port Packet takes the path F – E – A

Learning Switch A B Q 1 c) Node B wants to reach Node F C D E F G Flood or no? When do we stop? Nodes ACEF receive the packet Packet takes the path B-A-E-F

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

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

Link-State Routing A B C D

Link-State Routing Q 2 a) A 1 B 1 2 5 2 8 B C (1, A) (5, A) (3, B) ∞ (9, B) (1, A) (3, B) (7, C) D Node A C 4 D i 0 A C (1, B) 1 2 (1, B) (2, B) (8, B) (2, B) (6, C) Node B D

Link-State Routing Q 2 a) A 1 B 1 2 5 2 8 A B D (5, C) (3, B) (2, C) (4, C) Node C C 4 D i 0 A B C ∞ 1 2 (9, C) (7, B) (8, D) (6, C) (4, D) Node D

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

Link-State Routing Q 2 c) Cost of link BC = 20, B sends to C A 1 5 20 B B thinks shortest path is BAC A thinks shortest path is ABC 8 C 4 D B A… Cost: ∞