Routing Algorithm

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Routing Algorithm

• 2004. 11. 3
• Ahn Kook Jin

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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

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Routing Protocol and Algorithm

• Determining the path(route)

destination host
source host
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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

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Link State Routing Algorithm

• Each node broadcasts the identities and costs to
  its directly attached neighbors
• Dijkstras algorithm

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Link State Routing Algorithm

• Oscillation(page 307)

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Distance Vector Routing Algorithm

• Iterative, asynchronous, distributed
• Distance table
• DX(Y,Z) cost of the direct link from X to Z
  Zs currently known minmum-cost path to Y
• DX(Y,Z)c(X,Z)minwDz(Y,w)

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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

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Distance Vector Routing Algorithm
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Distance Vector Routing Algorithm
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Distance Vector Routing Algorithm
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Distance Vector Routing Algorithm

• Decrease

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Distance Vector Routing Algorithm

• Decrease

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Distance Vector Routing Algorithm

• Decrease

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Distance Vector Routing Algorithm

• Decrease

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Distance Vector Routing Algorithm

• Increase

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Distance Vector Routing Algorithm

• Increase

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Routing loop
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Distance Vector Routing Algorithm

• Increase

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Distance Vector Routing Algorithm

• Increase

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Distance Vector Routing Algorithm

• Increase

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Too many iterations! (count-to-infinity problem)
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Distance Vector Routing Algorithm

• Poisoned reverse

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Distance Vector Routing Algorithm

• Poisoned reverse

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Distance Vector Routing Algorithm

• Poisoned reverse

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Distance Vector Routing Algorithm

• Poisoned reverse

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Distance Vector Routing Algorithm

• Poisoned reverse
• Cannot solve general count-to-infinity problem

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LS Algorithm vs. DV Algorithm
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Hierarchical Routing

• View network as interconnected routers
• Scale
• Administrative autonomy
• Organize routers into autonomy systems(AS)

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Hierarchical Routing
Autonomy system(AS)Gateway routerIntra-ASInter-
AS
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Hierarchical Routing
Topological view for inter-AS routing protocol
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END