Routing ProtocolPertemuan 21

Matakuliah : H0484/Jaringan KomputerTahun : 2007

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Learning Outcomes

Pada akhir pertemuan ini, diharapkan mahasiswa

akan mampu :

• Menjelaskan Routing Protocol

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Outline Materi

• Interior Routing Protocol• External Routing

Protocol• Algorithm• Protocols

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Routing Protocols

• Routing Information– About topology and delays in the

internet• Routing Algorithm

– Used to make routing decisions based on information

• Routing algorithms are implemented using routing protocols

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Autonomous Systems (AS)

• Group of routers– Exchange information – Common routing protocol

• Set of routers and networks managed by single organization

• A connected network– There is at least one route between

any pair of nodes

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Autonomous systems

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Interior Routing Protocol

• Routing protocols that operate within a network (called an autonomous system) are called interior routing protocols.

• Passes routing information between routers within AS

• Routing algorithms and tables may differ between different AS

• IRP needs detailed model

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Exterior Routing Protocol

• Exterior router protocol (ERP) is used for operating outside of or between networks

• Because there are many more possible routes it is far more complex than interior routing

• It cannot maintain tables of every single route and have to concentrate instead on the main routes only.

• There may be more than one AS in internet• Routing algorithms and tables may differ between

different AS• Routers need some info about networks outside

their AS• ERP supports summary information on reachability

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Application of IRP and ERP

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Interior Routing Protocols - RIP

Routing Information Protocol (RIP)

• Routing protocol commonly used on the Internet.

• Computers using RIP broadcast routing tables every minute or so.

• Now used on simpler networks• The original dynamic distance vector

protocol

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Interior Routing Protocols - OSPF

Open Shortest Path First (OSPF)• Has overtaken RIP as the most popular interior

routing protocol on the Internet• Has the ability to incorporate traffic and error rate

measures in its routing decisions. • Sends updates state info, not entire routing tables,

and only to other routers (not broadcasting them)• Each router keeps list of state of local links to

network• Little traffic (less burdensome to the network since)

as messages are small and not sent often • Route computed on least cost based on user cost

metric using Link State Routing Algorithm - RFC 2328

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Dynamic Routing Algorithms

Routing Algorithms•Distance Vector:

which uses the least number of hops to decide how to route a packet

•Link Statewhich uses a variety of information types and takes into account such factors as congestion and response time to decide how to route a packet.

Because of its more sophisticated approach, link state routing algorithms have become

more popular than distance vector algorithms.

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Routing Distance vector

•Each node (router or host) exchange information with neighboring nodes (both are directly connected to same network)

•First generation routing algorithm for ARPANET•Node maintains vector of link costs for each

directly attached network and distance and next-hop vectors for each destination

•Requires transmission of lots of information by each router

– Distance vector to all neighbors– Contains estimated path cost to all networks

in configuration– Changes take long time to propagate

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Bellman-Ford Algorithm

• Find shortest paths from given node subject to constraint that paths contain at most one link

• Find the shortest paths with a constraint of paths of at most two links, and so on 

• s = source node• w(i, j) = link cost from node i to node j

– w(i, i) = 0– w(i, j) = if the two nodes are not directly connected– w(i, j) 0 if the two nodes are directly connected

• h = maximum number of links in path at current stage of the algorithm

• Lh(n) = cost of least-cost path from s to n under constraint of no more than h links

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Example of Bellman-Ford Algorithm

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Dijkstra’s Algorithm Definitions

• Djikstra's algorithm can accommodate weights on edges in graph

• Shortest path is then the path with lowest total weight (sum of weights of all edges)

• Shortest path not necessarily fewest edges (or hops)

• Find shortest paths from given source node to all other nodes, by developing paths in order of increasing path length

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ERP vs Distance vector

• Link-state and distance-vector not effective for exterior router protocol

• Distance-vector assumes routers share common distance metric

• ASs may have different priorities– May have restrictions that prohibit

use of certain other AS– Distance-vector gives no information

about ASs visited on route

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ERP vs Link-state

• Different ASs may use different metrics and have different restrictions– Impossible to perform a consistent

routing algorithm.• Flooding of link state information to

all routers unmanageable