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## PowerPoint Slideshow about 'Routing' - yamin

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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

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

- 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

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!

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

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

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

Link-State Routing What if the nodes don’t have the same map?

- Q2b) Node A sends to D
- Shortest path: ABCD
- Cost: 7

A

1

5

B

2

C

8

4

D

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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