1. Routing Networks and Protocols Prepared by: TGK First Prepared on: Last Modified on: Quality checked by: Copyright 2009 Asia Pacific Institute of Information Technology

2. Networks and Protocols Routing Slide 2 of 27 Topic & Structure of the lesson Routing Characteristics Routing Strategies Routing Algorithms

3. Networks and Protocols Routing Slide 3 of 27 Learning Outcomes At the end of this module, YOU should be able to: Discuss the characteristics required in performing routing functions Discuss the routing strategies used to determine appropriate communication path Discuss the operations of Link State and Distance Vector routing algorithms

4. Networks and Protocols Routing Slide 4 of 27 Key Terms you must be able to use If you have mastered this topic, you should be able to use the following terms correctly in your assignments and exams: Routing characteristics Routing strategies Routing algorithms

5. Networks and Protocols Routing Slide 5 of 27 Main Teaching Points Route selection Minimum hop Fixed Flood Random Adaptive Link State Distance Vector Dijkstra’s Bellman-Ford Link State Advertisements

6. Networks and Protocols Routing Slide 6 of 27 Routing Characteristics Complex, crucial aspect of packet switched networks Characteristics required Correctness and simplicity Robustness and stability Fairness and optimality Efficiency Used for selection of route Minimum hop Least cost

7. Networks and Protocols Routing Slide 7 of 27 Routing Characteristics

8. Networks and Protocols Routing Slide 8 of 27 Routing Strategies Fixed Flooding Random Adaptive Fixed: Single permanent route for each source to destination pair Determine routes using a least cost algorithm Route fixed, at least until a change in network topology Flooding RoutingFlooding Routing No network info required Packet sent by node to every neighbor

9. Networks and Protocols Routing Slide 9 of 27 Incoming packets retransmitted on every link except incoming link Eventually a number of copies will arrive at destination Each packet is uniquely numbered so duplicates can be discarded Nodes can remember packets already forwarded to keep network load in bounds Can include a hop count in packets Routing Strategies

10. Networks and Protocols Routing Slide 10 of 27 Figure 10.8 Flooding Example(hop count = 3) William Stalling –D&C Communication Routing Strategies

11. Networks and Protocols Routing Slide 11 of 27 Routing Strategies Properties of Flooding Routing All possible routes are tried Very robust At least one packet will have taken minimum hop count route Can be used to set up virtual circuit All nodes are visited Useful to distribute information (e.g. routing) Random RoutingRandom Routing Node selects one outgoing path for retransmission of incoming packet Selection can be random or round robin Can select outgoing path based on probability calculation

12. Networks and Protocols Routing No network information needed Route is typically not least cost nor minimum hop Adaptive RoutingAdaptive Routing Used by almost all packet switching networks Routing decisions change as conditions on the network change (failure, congestion, etc.) Requires information about network Decisions more complex Tradeoff between quality of network info and overhead Adaptive Routing ClassificationAdaptive Routing Classification Based on information sources Local (isolated) Route to outgoing link with shortest queue Can include bias for each destination Routing Strategies

13. Networks and Protocols Routing Slide 13 of 27 Rarely used - do not make use of easily available info Adjacent nodes All nodes Routing Strategies

14. Networks and Protocols Routing Slide 14 of 27 Routing Algorithms Distance Vector Also known as Bellman-Ford algorithm Passes periodic copies of a routing table Regular updates between routers communicate topology changes Perform routing decisions based on the information by neighboring routers Based on the distance (number of hops) and vector (direction) Before sending an update, each router adds its own distance value to the route's metric

15. Networks and Protocols Routing When a router receives an update, it maps the learned network to the receiving interface The router then uses that interface to reach those destinations Maintain a database of network topology information Send its entire routing table to each of its adjacent neighbors Router does not know the exact topology of an internetwork. Why? Update includes a list of subnets and the distances in metric Routing Algorithms

16. Networks and Protocols Routing Slide 16 of 27 Routers do not know the network topology except the neighboring routers If there’s multiple routes, chooses the best route which has the lowest metric Limitations Distance vector are classful routing protocols Do not send subnet information in updates Do not support scalability features such as Variable Length Subnet Masking (VLSM) or super-netting Converge slowly compared to link-state protocols – not suitable for complex and scalable internetworks Routing Algorithms

17. Networks and Protocols Routing Slide 17 of 27 Routing Algorithms Examples of Distance Vector Routing Protocol Routing Information Protocol (RIP) Interior Gateway Routing Protocol (IGRP) Enhanced IGRP (EIGRP) – balanced hybrid Border Gateway Protocol (BGP)

18. Networks and Protocols Routing Slide 18 of 27 Link State Uses Shortest Path First (SPF) algorithms/Dijkstra Algorithms Flood routing information to all routers in the internetwork that creates a map of the entire network Assemble all the information to calculate the shortest path routes and builds routing tables showing the best path Once converged, send update packets, which contain only changes rather than whole routing table Update packets are passed across the network in event- triggered updates Routing Algorithms

19. Networks and Protocols Routing Slide 19 of 27 Routing Algorithms Builds a complete database of all the link states Router gathers enough information to create the network map Each router individually runs the SPF algorithm on its link-state database to identify the best paths These paths form a tree with the local router as its root Advertise the states of their links to all other routers in the area

20. Networks and Protocols Routing When a network link changes state, a notification called a link-state advertisement (LSA) is flooded throughout the network All the routers note the change and adjust their routes accordingly Also has periodic re-flooding of LSA but longer interval time More reliable, easier to debug, and less bandwidth- intensive Link-state advertisements (LSAs) – routing information that is sent between routers Routing Algorithms

21. Networks and Protocols Routing Link-state advertisements (LSAs) – routing information that is sent between routers –Router LSA – identifies router ID, router interfaces IP addresses, status (up or down) of each interface, cost (metric) associated with each interface –Link LSA – identifies each subnet and routers that are attached to that subnet  Topological database – collection of information (data structure) gathered from LSAs  SPF algorithm – calculation performed on the database resulting in the SPF tree Routing Algorithms

22. Networks and Protocols Routing  Routing tables – A list of the known paths and interfaces  Advantages  Faster Convergence  Improved bandwidth utilization  Support Classless Inter-Domain Routing (CIDR), VLSM, and super-netting  Limitations  Processor overhead  Memory requirements  Bandwidth Consumption  Complex administration Routing Algorithms

23. Networks and Protocols Routing Slide 23 of 27 Quick Review Question

24. Networks and Protocols Routing Slide 24 of 27 Follow Up Assignment

25. Networks and Protocols Routing Slide 25 of 27 Summary of Main Teaching Points

26. Networks and Protocols Routing Slide 26 of 27 Q & A Question and Answer Session

27. Networks and Protocols Routing Slide 27 of 27 Topic and Structure of next session Networking and Internetworking Devices Repeaters Bridges Routers Gateways Next Session