1. COS 461: Computer Networks Spring 2013
Routing Recitation #3
COS 461: Computer Networks
Spring 2013

2. Outline
Fork()
Wireshark
Practice routing questions

3. Handle Multiple Clients using fork()
Steps to handle multiple clients
Go to a loop and accept connections using accept()
After a connection is established, call fork() to create a new child process to handle it
Go back to listen for another socket in the parent process
close() when you are done

4. while (1) { fd = accept (srv_fd, (struct sockaddr. ) &caddr, &clen);
while (1) { fd = accept (srv_fd, (struct sockaddr *) &caddr, &clen); ... pid = fork(); children++; /* child process to handle request */ if (pid == 0) { /* exit(0) on success, exit(1) on error */ } /* parent process */ else if (pid > 0) { while ((waitpid(-1, &status, WNOHANG)) > 0) children--; if (children > MAX_PROCESSES) else { perror("ERROR on fork"); exit(1); }}

5. Wireshark Selecting and listening on interface
Root for promiscuous mode: sniff on neighbors!
Writing filters to select packets
“udp.dstport == 53”, “http.request_method is present”
Examining packet formats
Look at Ethernet, IP, TCP, HTTP headers
Following TCP streams
Trace HTTP request(s) belonging to a TCP connection

6. Questions

7. Link State (Djikstra’s)
dest
link b
(a,?) 6 e d c
(a,?) 4 22 7 d
(a,?) b c 7 10 18 e
(a,?) a f 4 f
(a,?)

8. Link State (Djikstra’s)
dest
link b
(a,b) 6 e d c
(a,?) 4 22 7 d
(a,?) b c 7 10 18 e
(a,?) a f 4 f
(a,?)

9. Link State (Djikstra’s)
dest
link b
(a,b) 6 e d c
(a,f) 4 22 7 d
(a,?) b c 7 10 18 e
(a,?) a f 4 f
(a,?)

10. Link State (Djikstra’s)
dest
link b
(a,b) 6 e d c
(a,f) 4 22 7 d
(a,f) b c 7 10 18 e
(a,?) a f 4 f
(a,?)

11. Link State (Djikstra’s)
dest
link b
(a,b) 6 e d c
(a,f) 4 22 7 d
(a,f) b c 7 10 18 e
(a,f) a f 4 f
(a,?)

12. Link State (Djikstra’s)
dest
link b
(a,b) 6 e d c
(a,f) 4 22 7 d
(a,f) b c 7 10 18 e
(a,f) a f 4 f
(a,f)

13. Which routing protocol requires the least amount of state on the router?
link state
distance vector
path vector

14. Which routing protocol requires the least amount of state on the router?
link state
distance vector
path vector

15. Which of the following, if true, ensures packets from a to e always traverse c?
B. Y > X + 1
C. Y > X
D. A or B D

16. Which of the following, if true, ensures packets from a to e always traverse c?
B. Y > X + 1
C. Y > X
D. A or B D

17. Which of the following, if true, ensures packets from b to e always traverse d?
B. Y > X + 1
C. Y > X
D. A or B B

18. Which of the following, if true, ensures packets from b to e always traverse d?
B. Y > X + 1
C. Y > X
D. A or B B

19. Distance Vector Routing Initial Routing table at E18 C 21 11 12 5 A D E 15 17
Initial Routing table at E
Destination
Cost
Next Hop A B C D

20. Distance Vector Routing Initial Routing table at E18 C 21 11 12 5 A D E 15 17
Initial Routing table at E
Destination
Cost
Next Hop A
Inf
--- B C D

21. Distance Vector Routing Initial Routing table at E18 C 21 11 12 5 A D E 15 17
Initial Routing table at E
Destination
Cost
Next Hop A
Inf
--- B C D

22. Distance Vector Routing Initial Routing table at E18 C 21 11 12 5 A D E 15 17
Initial Routing table at E
Destination
Cost
Next Hop A
Inf
--- B C 11 D

23. Distance Vector Routing Initial Routing table at E18 C 21 11 12 5 A D E 15 17
Initial Routing table at E
Destination
Cost
Next Hop A
Inf
--- B C 11 D 17

24. Distance Vector Routing Routing table at E after one iteration18 C 21 11 12 5 A D E 15 17
Routing table at E after one iteration
Destination
Cost
Next Hop A
Inf
--- B C 11 D 17

25. Distance Vector Routing Routing table at E after one iteration18 C 21 12 5 11 A D E 15 17
Routing table at E after one iteration
Destination
Cost
Next Hop A 32 D B
Inf
--- C 11 17

26. Distance Vector Routing Routing table at E after one iteration18 C 21 12 5 11 A D E 15 17
Routing table at E after one iteration
Destination
Cost
Next Hop A 32 D B 29 C 11 17

27. Distance Vector Routing Routing table at E after one iteration18 C 21 12 5 11 A D E 15 17
Routing table at E after one iteration
Destination
Cost
Next Hop A 32 D B 29 C 11 17

28. Distance Vector Routing Routing table at E after one iteration18 C 21 12 5 11 A D E 15 17
Routing table at E after one iteration
Destination
Cost
Next Hop A 32 D B 29 C 11 16

29. Distance Vector Routing Routing table at E after two iterations18 C 21 12 5 11 A D E 15 17
Routing table at E after two iterations
Destination
Cost
Next Hop A 32 D B 29 C 11 16

30. Distance Vector Routing Routing table at E after two iterations18 C 21 12 5 11 A D E 15 17
Routing table at E after two iterations
Destination
Cost
Next Hop A 31 C B 29 11 D 16

31. Distance Vector Routing Routing table at E after two iterations18 C 21 12 5 11 A D E 15 17
Routing table at E after two iterations
Destination
Cost
Next Hop A 31 C B 28 11 D 16

32. Distance Vector Routing Routing table at E after two iterations18 C 21 12 5 11 A D E 15 17
Routing table at E after two iterations
Destination
Cost
Next Hop A 31 C B 28 11 D 16

33. Distance Vector Routing Routing table at E after two iterations18 C 21 12 5 11 A D E 15 17
Routing table at E after two iterations
Destination
Cost
Next Hop A 31 C B 28 11 D 16

34. Distance Vector RoutingB 18 C X 12 5 11 A D E 15 17
For what value of x does the routing table at E not change anymore after two iterations?
For all X >= 2
For all X >= 3
For all X <= 4
For all X <= 3

35. Distance Vector RoutingB 18 C X 12 5 11 A D E 15 17
For what value of x does the routing table at E not change anymore after two iterations?
For all X >= 2
For all X >= 3
For all X <= 4
For all X <= 3