1. Lecture 17 November 8Intra-domain routing November 13Internet routing 1 November 15Internet routing 2 November 20End-to-end protocols 1 November 22End-to-end protocols 2 November 27End-to-end protocols 3 November 29Exam 4 December 8Exam 5 and Final

2. Routing versus Forwarding Network Number InterfaceMAC Address 10if08:0:2b:e4:b:1:2 Network NumberNext Hop 10171.69.245.10 Routing Table: Forwarding Table:

3. Why routing protocols? Link failures New nodes Congestion Two approaches: –Distance Vector-based on local information –Link State-based on global information

4. Distance-vector routing DestinationCostNext Hop B  B C  C D  C E1E F1F G  F

5. Routing Loops Example 1 –F detects that link to G has failed –F sets distance to G to infinity and sends update t o A –A sets distance to G to infinity since it uses F to reach G –A receives periodic update from C with 2-hop path to G –A sets distance to G to 3 and sends update to F –F decides it can reach G in 4 hops via A Example 2 –link from A to E fails –A advertises distance of infinity to E –B and C advertise a distance of 2 to E –B decides it can reach E in 3 hops; advertises this to A –A decides it can read E in 4 hops; advertises this to C –C decides that it can reach E in 5 hops…

6. Loop- Breaking Heuristics Set infinity to 16 Split horizon Split horizon with poison reverse

7. Router Information Protocol (RIP)

8. RIP packet

9. Link State Routing Each node establishes a list of directly connected neighbors and cost of each link Floods that information in a LSP to all neighbors Retransmits LSPs from other nodes- but does not echo to sender

10. Propagation of LSPs

11. LSP Information ID of sending node Link-state of sending node Sequence number Time to live

12. Route Calculation Each node has enough information to map the network Dijkstra’s shorted path algorithm used to compute the routes

13. Example: Link State Routing

14. Routing Table Calculation StepConfirmed TentativeComments 1 2 3 4

15. Routing Table Calculation StepConfirmedTentativeComments 5 6

16. Routing Table Calculation StepConfirmedTentativeComments 7

17. OSPF Authentication Hierarchy-Domains and Areas Load Balancing

18. OSPF Header Format

19. OSPF link-state advertisement

20. Metrics Issues –Number of Hops –Latency –Bandwidth or Capacity –Congestion Difficult to assign a scalar cost to such a complex and changing problem

21. ARPANET 1 Lowest Cost=Shortest Queue

22. ARPANET 2 Delay=(Depart time-Arrival Time)+Transmission Time+Latency Reliability incorporated through the Depart Time parameter Wide spread of weights- Oscillations

23. ARPANET 3 Reduce dynamic range of metric Averaging Hard limit on changes in metric-like the stock market