Pertemuan 20 Teknik Routing

1. Matakuliah : H0174/Jaringan Komputer Tahun : 2006 Versi : 1/0 Pertemuan 20Teknik Routing

2. Learning Outcomes Pada akhir pertemuan ini, diharapkan mahasiswa akan mampu : • Menunjukkan teknik routing

3. Outline Materi • Routing table • Routing Algorithm • Routing Protocol

4. Routing • Routing is the process of deciding what path to take from sender to receiver (packet forwarding) • Usually there is more than one route possible; devices that perform routing must keep tables to make decisions about which path to send packets on to reach a given destination (routing table) • Routing decisions on the Internet are usually handled by special purpose devices called Routers, that maintain their own routing tables • End systems and routers maintain routing tables • Routing table indicates next router to which datagram should be sent

5. Performance Criteria • Number of hops • Cost • Delay • Throughput • Decision Time • Packet (datagram) • Session (virtual circuit) • Decision Place • Each node (distributed) • Central node (centralized) • Originating node (source) • Network Information Source • None • Local • Adjacent node • Nodes along route • All nodes • Network Information Update Timing • Continuous • Periodic • Major load change • Topology change Routing Techniques Criteria

6. Routing Strategies • Fixed • Flooding • Random • Adaptive

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. Dynamic Routing Algorithms Routing Algorithms • Distance Vector: which uses the least number of hops to decide how to route a packet • Link State which 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.

14. 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

15. 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

16. Link-state Routing • Designed to overcome drawbacks of distance-vector • When router initialized, it determines link cost on each interface • Advertises set of link costs to all other routers in topology and not just neighboring routers • Then monitor link costs, if significantly changes, router advertises new set of link costs • Each router can construct topology of entire configuration and can calculate shortest path to each destination network

17. Least Cost Algorithms • Basis for routing decisions • Can minimize hop with each link cost 1 • Can have link value inversely proportional to capacity • Given network of nodes connected by bi-directional links each link has a cost in each direction • Define cost of path between two nodes as sum of costs of links traversed • For each pair of nodes, find a path with the least cost • Link costs in different directions may be different e.g. length of packet queue

18. Dijkstra’s Algorithm • 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

19. Bellman vs Dijkstra • Results from two algorithms agree • Bellman-Ford • Calculation for node n involves knowledge of link cost to all neighboring nodes plus total cost to each neighbor from • Each node can maintain set of costs and paths for every other node • Can exchange information with direct neighbors, can update costs and paths based on information from neighbors and knowledge of link costs • Dijkstra • Each node needs complete topology • Must know link costs of all links in network • Must exchange information with all other nodes