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# Routing - PowerPoint PPT Presentation

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

EE122 Section 4

Application

Transport

Mostly still here

Network

Physical

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

B

A

C

D

E

G

F

Every node can reach G by following the arrows

B

A

C

D

E

G

F

Every node can reach E by following the arrows

• Easiest way to reach destination is Flooding

B

A

C

D

E

G

F

• Wasteful  Motivation for 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!

• 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

Q1d)

1

1

1

1

3

1

Node A

Node B

Node C

Node D

Q1d)

1

1

1

1

1

2

Node E

Node F

Node G

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

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

• 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

• 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