COMPUTER NETWORKS (MCA) – QUIZ 1 (8/9/2016)

1. If the destination address is 127.0.0.1, what does the IP layer do?

2. How many networks are possible in Class C networks?

3. If the net mask is 255.248.0.0, how many networks are possible in this organization?

   (Ans: 2**13 networks as there are 13 bits in the network ID)

4. If the net mask is 255.255.255.192, how many hosts are possible per network?

   (Ans: 2**6 – 2 hosts = 62)

5. If the IP address is 128.0.0.1, which class does this belong to and what is its net mask?

   (Ans: Class B, 255.255.0.0)

6. If two addresses are 10.5.0.1 and 10.5.6.1 and the net mask is 255.255.252.0, do they belong to the same or different networks and which network(s)?

   (Ans: They belong to diff. networks as masking them with the subnet mask given results in 10.5.0.0 and 10.5.4.0 for both.)

7. If the IP address given is 202.41.85.198/25, what is the network ID of the network this host belongs to?

   (Ans: 202.41.85.128)

8. If the IP address given is 202.41.85.117/26, what is the broadcast ID of the network, this host belongs to?

   (Ans: 202.41.85.127)

9. Given that the IP address of a host is 10.200.1.20/9, what is the first host ID of this network?

   (Ans: 10.128.0.1)

10. Given that an organization uses 11 bits for network ID, what is the net mask?

    (Ans: 255.224.0.0)

11. How many networks are possible with class B addressing?

    (Ans: 64*256 = 2**14 = 16K)

12. What is the purpose of ARP?

13. What does the address 224.0.0.1 mean?

14. If the destination address of an IP header is 202.41.85.255, what does this mean?

15. If the MF=1 and FO = 4460, what does this represent?

16. If MF=0, FO=2960 and Length=580, what is the length of the datagram?

17. What happens if a fragment is lost?

18. State two reasons why ARP maintains a cache and not a table?

19. How is the checksum calculated in IP?

20. Why is ID field alone not sufficient to identify fragments of an IP datagram?

21. If the IP destination address is a broadcast address, do we need to do ARP?

22. How is it that the default route is able to match every network in the world?

23. What is the use of the interface field in the forwarding table?

24. How is the gateway address of a routing table entry determined?

25. What are the services offered by the network layer?

26. A router has three networks it is connected to and its IP addresses are 202.41.85.1/24(eth0), 172.16.88.1/21(eth1) and 10.5.0.1/23(eth2). A host with IP address 10.5.0.21 wants to communicate with a host with IP address 172.16.88.12. Give the source and destination IP and MAC addresses of the packet from source to destination.

27. A router has an entry as follows: 202.41.85.117/32. What is this route?

28. If there are three entries in the routing table of a router as follows:

    10.0.0.0 255.0.0.0 eth0 d

    10.0.4.0 255.255.0.0 eth1 d

    10.0.5.0 255.255.255.0 eth2 d

    which of them is matched for 10.0.6.1, 10.0.5.1 and 10.1.1.1?

29. If a router sees that the IP header has DF=1, what does it tell the router?

30. If, in a network, there are two routers between H1 and H2, what should be the minimum value of TTL such that communication between H1 and H2 is possible?