Routing
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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

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Routing

Routing

Flooding, Link-State

EE122 Section 4


First off where are we

First off, where are we?

Application

Transport

Mostly still here

Network

Datalink

Physical


Flooding

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


Routing

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


Routing

Spanning Tree Rooted at G

B

A

C

D

E

G

F

Every node can reach G by following the arrows


Routing

Spanning Tree Rooted at E

B

A

C

D

E

G

F

Every node can reach E by following the arrows


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

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 switch1

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


Learning switch2

Learning Switch

Q1d)

1

1

1

1

3

1

Node A

Node B

Node C

Node D


Learning switch3

Learning Switch

Q1d)

1

1

1

1

1

2

Node E

Node F

Node G


Link state routing

Link-State Routing

A

B

C

D


Link state routing1

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 routing2

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 routing3

Link-State Routing

  • 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


    Link state routing4

    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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