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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 costs 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
