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Routing

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Routing

Flooding, Link-State

EE122 Section 4

Application

Transport

Mostly still here

Network

Datalink

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

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

- 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

- 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

A

B

C

D

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

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