1. Static versus Dynamic Routes Static Route Uses a protocol route that a network administrators enters into the router Static Route Uses a protocol route that a network administrators enters into the router Dynamic Route Uses a route that a network routing protocol adjusts automatically for topology or traffic changes Dynamic Route Uses a route that a network routing protocol adjusts automatically for topology or traffic changes

2. Static Route Example A B Point-to-point or circuit-switched connection Only a single network connection with no need for routing update “Stub” Network Fixed route to address reflects administrator’s knowledge

3. Default Route Example Use if next hop is not explicitly listed in the routing table A B C 192.34.56.0 10.0.0.0 Company X Internet Routing Table No entry for destination net Try router B deafult route

4. Adapting to Topology Change C B A D X Can alternate route substitute for a failed route ?

5. Dynamic Routing Operations Routing protocol maintains and distributes routing information Network Routing Protocol Routing table Routing table Routing table Routing table

6. Representing Distance with Metrics Information used to select the best path for routing B A E1 64 Bandwidth Delay Load Reliability Bandwidth Delay Load Reliability Hop count Ticks Cost Hop count Ticks Cost

7. Classes of Routing Protocols C B A D C B A D Distance Vektor Hybrid Routing Link State

8. One Issue: Time to Convergence Convergence occurs when all routers use a consistent perspective of network topology After a topology changes, routers must recompute routes, which disrupts routing The process and time required for router reconvergence varies in routing protocols

9. Distance Vector Concept Pass periodic copies of routing table to neighbor routers and accumulate distance vectors C B A D D C B A Routing Table Routing Table Routing Table Routing Table Routing Table Routing Table Routing Table Routing Table

10. Distance Vector Network Discovery B A C W X Y Z Routing Table X 0 Y 0 Z 1 W 1 Routing Table X 0 Y 0 Z 1 W 1 Routing Table Y 0 Z 0 X 1 W 2 Routing Table Y 0 Z 0 X 1 W 2 Routers discover the best path to destinations from each neighbor Routing tábla W 0 X 0 Y 1 Z 2 Routing tábla W 0 X 0 Y 1 Z 2

11. Distance Vector Topology Changes Updates proceed step-by-step from router to router B A TopologyChangeCausesRoutingTableUpdate Process to Update This Routing Table Router A Sends Out This UpdatedRoutingTable Process to Update This Routing Table

12. Problem: Routing Loops A E D C B X 1 Alternate Route: Network 1, Distance 3 Alternate Route: Network 1, Distance 3 Network 1, Unreachable Alternate Route: Use A Network 1, Distance 4 Alternate Route: Use A Network 1, Distance 4 Alternate routes, slow convergence, inconsistent routing Network 1 Down

13. Problem:Counting to Infinity A E D C B X 1 Network 1, Distance 5 Network 1, Distance 7 Network 1, Distance 4 Network 1, Distance 6 Routing loops increment the distance vector Network 1 Down

14. Routing Table Maximum metric is 16 Network 1 is Unreachable Routing Table Maximum metric is 16 Network 1 is Unreachable Solution: Defining a Maximum A E D C B X 1 Network 1, Distance 12 Network 1, Distance 14 Network 1, Distance 15 Network 1, Distance 13 Specify a maximum distance vector metric as infinity Network 1 Down

15. Network 1, unreachable Solution: Split Horizon If you learn a protocol’s route on an interface, do not send information about that route back out that interface A E D C B X 1 Network 1 Down B:Do not update router A about routes to network 1 D: Do not update router A about routes to network 1

16. Network 1 route to network 1 has infinite Cost Network 1 route to network 1 has infinite Cost Solution: Route Poisoning Router keeps an entry for the network down state, allowing time for other routers to recompute for this topology change A E D C B X 1 Network 1 Down

17. Solution: Hold-Down Timers Routers ignore network update information for some period A E D C B ?,X 1 Network 1 Down Update after Hold-Down Time Update after Hold-Down Time Network 1 Down Update after Hold-Down Time Update after Hold-Down Time Update after Hold-Down Time Update after Hold-Down Time Update after Hold-Down Time Update after Hold-Down Time

18. Link-State Concept After initial flood, pass small event-triggered link-state updates to all other routers A D C B Link-State Packets Topological Database Shortest Path First Tree Routing Table Routing Table SPF Algorithm

19. Link-State Network Discovery B A C W X Y Z Link-State Packet W 0 X 0 Link-State Packet W 0 X 0 Link-State Packet X 0 Y 0 Link-State Packet X 0 Y 0 Link-State Packet Y 0 Z 0 Link-State Packet Y 0 Z 0 Topological Database Topological Database Topological Database SPF A Routing Table A Routing Table B Routing Table B Routing Table C Routing Table C Routing Table SPF Tree Routers calculate the shortest path to destinations in paralell

20. Link-State Topology Changes Topology Change in Link- State Update Process to Update This Routing Table Update processes proceed using the same link-state update Process to Update This Routing Table

21. Link-State Concerns Topological Database SPF Routing Table Routing Table SPF Tree Processing and memory required for link-state routing Bandwidth consumed for initial link state „flood”

22. Problem: Link-State Updates A D C B Network 1, Back Up Now Network 1, Unreachable X,ok Slow path update Slow path update arriveslast Network 1 goes down then comes up Fast path updates arrive first Which SPF tree to use for routing? Unsynchronized updates, inconsistent path decisions

23. Link-State Update Problems (cont.) Synchronizing large networks- which network topology updates are correct? Router startup-order of start alters the topology learned Partitioned regions-slow updating part separated from fast updating part

24. Solution: Link-State Mechanisms Reduce the need for resources ”Dampen” update frequncy Target link-state updates to multicast Use link-state area hierarchy for topology Exchange route summaries at area borders Reduce the need for resources ”Dampen” update frequncy Target link-state updates to multicast Use link-state area hierarchy for topology Exchange route summaries at area borders Coordinate link-state updates Use time stamps Update numbering and counters Manage partitioning using an area hierarchy Coordinate link-state updates Use time stamps Update numbering and counters Manage partitioning using an area hierarchy

25. Comparing Distance Vector Routing to Link-State Routing Distance Vector Link-State Views net topology from Gets common view of neighbor’s perspective entire network topology Adds distance vectors Calculates the shortest from router to router path to other routers Frequent, periodic updates: Event-triggered updates: slow convergence faster convergence Passes copies of routing Passes link-state routing updates table to neighbor routers to other routers Distance Vector Link-State Views net topology from Gets common view of neighbor’s perspective entire network topology Adds distance vectors Calculates the shortest from router to router path to other routers Frequent, periodic updates: Event-triggered updates: slow convergence faster convergence Passes copies of routing Passes link-state routing updates table to neighbor routers to other routers

26. Hybrid Routing Choose a routing path based on distance vectors Convergence rapidly using change-based updates Balanced Hybrid Routing Share attributes of both distance-vector and link-state routing EIGRP