Routing algorithm

Routing Algorithm

2004. 11. 3Ahn Kook Jin

Contents Routing Protocol and Algorithm Classifications Link State Routing Algorithm Distance Vector Routing Algorithm LS Algorithm vs. DV Algorithm Hierarchical Routing

Routing Protocol and Algorithm Determining the path(route)

5

2

12 3

1

35

21

B

A

C E

D

F

source host

destination host

first-hop routerdefault router

source router

destination router

least-cost path

Classifications Global vs. decentralized

global(link state algorithm) : complete information about connectivity and link costs

Static vs. dynamic static : routes change very slowly

Load-sensitive vs. load-insensitive load-sensitive : link costs reflect congestion

Typical used Dynamic link state routing algorithm Dynamic distance vector routing algorithm

Link State Routing Algorithm Each node broadcasts the identities and cost

s to its directly attached neighbors Dijkstra’s algorithm

Link State Routing Algorithm Oscillation(page 307)

D B

C

A

e

11

2+e 0

0

1+e 00

0

1

10

0

0e0

1+e

0

00

0

01+e

1

2+e

0

2+e 0

0

1+e 00

0

1

Distance Vector Routing Algorithm Iterative, asynchronous, distributed Distance table

DX(Y,Z) : cost of the direct link from X to Z + Z’s currently known minmum-cost path to Y

DX(Y,Z)=c(X,Z)+minw{Dz(Y,w)}

Distance Vector Routing Algorithm Initialization:

DX(*,v) = inifinite, DX(v,v)=c(x,v) Send minwDX(y,w) to each neighbor when they

changes C(X,V) changes Neighbor node send its update

Distance Vector Routing Algorithm

Y

X Z7

2 1

DX Y Z

Y 2 ∞

Z ∞ 7

DY X Z

X 2 ∞

Z ∞ 1

Dz X Y

X 7 ∞

Y ∞ 1

Distance Vector Routing Algorithm

Y

X Z7

2 1

DX Y Z

Y 2 8

Z 3 7

DY X Z

X 2 8

Z 9 1

Dz X Y

X 7 3

Y 9 1

Distance Vector Routing Algorithm

Y

X Z7

2 1

DX Y Z

Y 2 8

Z 3 7

DY X Z

X 2 4

Z 5 1

Dz X Y

X 7 3

Y 9 1

Distance Vector Routing Algorithm

Y

X Z50

4 1

DY X Z

X 4 6

Dz X Y

X 50 5

1

Decrease

Distance Vector Routing Algorithm

Y

X Z50

4 1

DY X Z

X 1 6

Dz X Y

X 50 5

1

Decrease

Distance Vector Routing Algorithm

Y

X Z50

4 1

DY X Z

X 1 6

Dz X Y

X 50 2

1

Decrease

Distance Vector Routing Algorithm

Y

X Z50

4 1

DY X Z

X 1 6

Dz X Y

X 50 2

1

Decrease

Distance Vector Routing Algorithm Increase

Y

X Z50

4 1

DY X Z

X 4 6

Dz X Y

X 50 5

60

Distance Vector Routing Algorithm Increase

Y

X Z50

4 1

DY X Z

X 60 6

Dz X Y

X 50 5

60 Routing loop

Distance Vector Routing Algorithm Increase

Y

X Z50

4 1

DY X Z

X 60 6

Dz X Y

X 50 7

60

Distance Vector Routing Algorithm Increase

Y

X Z50

4 1

DY X Z

X 60 8

Dz X Y

X 50 7

60

Distance Vector Routing Algorithm Increase

Y

X Z50

4 1

DY X Z

X 60 8

Dz X Y

X 50 9

60 Too many iterations!

(count-to-infinity problem)

Distance Vector Routing Algorithm Poisoned

reverse

Y

X Z50

4 1

DY X Z

X 4 ∞

Dz X Y

X 50 5

60

Distance Vector Routing Algorithm Poisoned

reverse

Y

X Z50

4 1

DY X Z

X 60 ∞

Dz X Y

X 50 5

60

Distance Vector Routing Algorithm Poisoned

reverse

Y

X Z50

4 1

DY X Z

X 60 ∞

Dz X Y

X 50 61

60

Distance Vector Routing Algorithm Poisoned

reverse

Y

X Z50

4 1

DY X Z

X 60 51

Dz X Y

X 50 61

60

Distance Vector Routing Algorithm Poisoned

reverse

Cannot solve general count-to-infinity problem

Y

X Z50

4 1

DY X Z

X 60 51

Dz X Y

X 50 ∞

60

LS Algorithm vs. DV Algorithm

LS DV

Message complexity

O(nE) Maybe small

Speed of convergence

O(n2) algorithm Slow(count-to-infinity problem)

Robustness Good Bad

Hierarchical Routing View network as interconnected routers

Scale Administrative autonomy

Organize routers into autonomy systems(AS)

Hierarchical Routing

B.aB.a

A.a

A.b

A.cA.d

C.b

C.c

C.a

Host H1

Host H2

Autonomy system(AS)Gateway routerIntra-ASInter-AS

Hierarchical Routing

B.a

A.a

A.c

C.a

Topological view for inter-AS routing protocol

END