1. Routing
Flooding, Link-State
EE122 Section 4

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

3. 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

4. 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

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

6. Spanning Tree Rooted at EB 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 E G A C D B F
Wasteful  Motivation for Learning Switch

8. 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!

9. 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

10. 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

11. 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

12. Link-State Routing A C B D

13. 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

14. 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

15. 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

16. 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