1. RFC 1058 & RFC 2453 Routing Information Protocol
RIP v1 and v2
RFC 1058 & RFC 2453
Routing Information Protocol

13. Illustration1
Good case

14. Distance Vector Network Discovery E0 A S0 B C S0 S1 S0 E0
Routing Table
Routing Table
Routing Table E0 S0 S0 S1 S0 E0
Routers discover the best path to destinations from each neighbor

15. Distance Vector Network Discovery E0 A S0 B C S0 S1 S0 E0
Routing Table
Routing Table
Routing Table E0 S0 S0 S1 S0 E0 1 1 S0 1 1
Routers discover the best path to destinations from each neighbor

16. Distance Vector Network Discovery E0 A S0 B C S0 S1 S0 E0
Routing Table
Routing Table
Routing Table E0 S0 S0 S1 S0 E0 1 1 S0 1 2 1 S0 2
Routers discover the best path to destinations from each neighbor

17. Illustration2
Bad case

18. Distance Vector Topology Changes
Process to update this routing
table
Topology
change
causes
routing
update
Updates proceed step-by-step from router to router

19. Distance Vector Topology Changes
Process to update this routing
table
Router A
sends out this
updated
routing
Topology
change
causes
update
Updates proceed step-by-step from router to router

20. Distance Vector Topology ChangesB
Process to update this routing
table
Router A
sends out this
updated
routing
Topology
change
causes
update
Updates proceed step-by-step from router to router

21. Problem: Routing Loops E0 A S0 B C S0 S1 S0 E0
Routing Table E0 S0 1 2
Routing Table S0 S1 1
Routing Table S0 E0 1 2
Each node maintains the distance from itself to each possible destination network

22. Problem: Routing Loops X E0 A S0 B C S0 S1 S0 E0
Routing Table S0 E0 1 2
Down S1
Slow convergence produces inconsistent routing

23. Problem: Routing Loops X E0 A S0 B C S0 S1 S0 E0
Routing Table S0 E0 1 2 S1
Router C concludes that the best path to network is through Router B

24. Problem: Routing Loops X E0 A S0 B C S0 S1 S0 E0
Routing Table S0 1 2 E0 4 S1 3
Router A updates its table to reflect the new but erroneous hop count

25. Symptom: Counting to Infinity X E0 A S0 B C S0 S1 S0 E0
Routing Table S0 1 2 5 E0 3 S1 4
Packets for network bounce between routers A, B, and C, incrementing hop count

26. Solution: Defining a Maximum X E0 A S0 B C S0 S1 S0 E0
Routing Table E0 S0 1 16
Routing Table S0 S1 16 1
Routing Table S0 16 1 2
Define a limit on the number of hops to prevent infinite loops

27. Solution: Split Horizon X E0 A S0 B C S0 S1 S0 E0 X X
Routing Table S0 1 2 E0 S1 E1
It is never useful to send information about a route back in the direction from which the original packet came

28. Solution: Poison Reverse X E0 A S0 B C S0 S1 S0 E0
Routing Table E0 S0 1 2
Routing Table S0 S1 E1 1 2
Routing Table S0
Infinity 1 2
Routers set the distance to infinity if the destination is routed on that link

29. Solution: Hold-Down Timers
Network
is unreachable
Update after
hold-down Time X E0 A S0 B C S0 S1 S0 E0
Update after
hold-down Time
Network is down
then back up
then back down
Router keeps an entry for the network down state, allowing time for other routers to recompute for this topology change

30. Solution: Triggered Updates
Network
is unreachable
Network
is unreachable
Network
is unreachable X E0 A S0 B C S0 S1 S0 E0
Nodes send messages as soon as they notice a change in their routing table

31. Implementing Solutions in Multiple RoutesD E B X C
Routing Table
Infinity E0 A

32. Implementing Solutions in Multiple Routes (cont.)
Network
is possibly down D E B X C
Update after
holddown time A
Network
is possibly down

33. Implementing Solutions in Multiple Routes (cont.)D
Update after
holddown time
Network
is possibly down E B X C
Network
is possibly down A
Update after
holddown time

34. Implementing Solutions in Multiple Routes (cont.)D
Update after
holddown time
Update after
holddown time E B X C
Packet for
Network A
Update after
holddown time