Sample Questions

  1. Describe the effect propagation delay has on the transmission rate when using a simple stop-and-wait protocol. Use figures to show what is causing the delays. Explain why the effect worsens as the propagation delay increases.

  2. Example how a sliding window protocol improves performance, and how this relates to propagation delay. Explain what window size means. Will increasing the window size always increase performance? Why or why not?

  3. What is piggybacking? How does it affect performance? Does it have any disadvantages?

  4. Describe the flooding routing strategy. Explain in what way it is optimal. Explain how packets are kept from circulating forever.

  5. Define Flow Control and Congestion Control. Compare and contrast. What methods are used for each in TCP? How about with UDP?

  6. Consider CSMA/CD technique. Describe what is meant by the Carrier Sense (CS), Multiple Access (MA), and Collision Detect (CD). What types of topologies are compatible with CSMA/CD .

  7. What is CSMA/CA as used by 802.11? Why is this used instead of CSMA/CD?

  8. What is the hidden node problem in 802.11? What does 802.11 do to minimize the problem?

  9. List the major disadvantages with the layered approach to protocols.

  10. Describe the functions of a bridge, a router, and a gateway in terms of the levels at which they operate. For each, what level of the protocol do they operate? Compare and contrast the functionality of each of these devices.

  11. Describe the difference in the way packets are fragmented in IPv4 and IPv6. How and where is the fragment size decision made in each.

  12. What is a bridge? What services does it provide?

  13. What is a router? What services does it provide?

  14. What is the difference between non-adaptive and adaptive routing? Know which routing algorithm is which type. For Routing, what is the optimality principle?

  15. What is Distance vector routing? Give and example by taking a given network, and finding the appropriate path.

  16. What is link state routing? What are link state packets?

  17. What is hierarchical routing? Why is it used?

  18. What is a VLAN? How are packets modified to achieve VLANing? Why would a VLAN be used?

  19. What is tunneling? What is it useful for?

  20. What is packet fragmentation? Why does it happen? Where are the packets reassembled? What happens to a packet if part of it is missing?

  21. What is the difference between IP address classes A, B, C, and D? Why are there different classes? How can you determine the class of an address? What are some of the problems caused by this addressing technique? How can the use of subnets fix some of these problems?

  22. What is the meaning and purpose of CIDR? What problem does it help to solve? What is needed in addition to an IP address in order to correctly route a packet?

  23. Show how CIDR could be used to allocate 2048 addresses starting at 72.125.16.0. What is the CIDR notation? What is the address range?

  24. What is an ARP packet? What are it’s significant fields? What is its purpose? Describe how it works.

  25. What class does an IP address belong to that starts with the binary pattern 110 as the three leftmost bits?

  26. What is the purpose of the Internet Control Message Protocol (ICMP)? Give three examples of ICMP messages.

  27. What is the purpose of the Reverse Address Resolution Protocol ? What is it used for?

  28. In a subnet, what is the host ID and network ID ?How large is the subnet ID field on a Class B network with the mask 255.255.224.0? How large is the host ID field? How many subnets can there be in this case (assuming all use the same subnet field size). How many host on each subnet? If Network the address is 136.192.0.0, What is the range of each subment?

  29. A network admin calculates that he'll need 25 mask bits for his network. What subnet mask should he use? How many computers will be on each subnet? Which class address is this mask compatible with (A, B, and/pr C)?

  30. You have a Class C network address. You also have employees in 10 different cities, and you would like a subnet for each city, and each city has no more than 12 people. What subnet mask or masks would enable you to assign a distinct address for each user?

  31. Bill Yeakus wants to use four subnet bits for subnetting on a Class A network. What should he use for a subnet mask? What is the size of each subnet, and how many subnets can there be?

  32. What is the range of IP addresses assigned for the CIDR range 212.100.192.0/20?

  33. What are multiplexing and demultiplexing and how are they used in IP for UDP and TCP? Why are they important?

  34. Why might a developer prefer to use the UDP instead of the TCP protocol? Give 3 distinct examples with justification.

  35. What are the three steps of setting up a TCP connection? Why is the third step in the three-way handshake TCP necessary?

  36. What are the main fields in the header of a UDP packet? How many bits are each? Which field in the UDP header is optional and why?

  37. Given TCP and UDP, which is stream oriented, and which is packet oriented? Which involves a connection, and which is connectionless?

  38. What is a well-known port? Given 3 examples.

  39. What is static and dynamic routing? What is used on the internet and why?

  40. At what layer does a hub and switch communicate? What is the difference between the two? Generally, which is better and why?

  41. What is a multihomed computer?

  42. If a computer has two network interfaces, why must it be configured for IP forwarding before it will act as a router?

  43. Why is link state routing better for larger networks?

  44. What is the purpose of the exterior router? What is an AS, and what does it have to do with an exterior router?

  45. What are RIP and OSPF? Which uses link state routing and which distance vector routing? RIP and OSPF?

  46. What is DHCP? What exactly happens (in terms of packets) when a system starts up using DHCP?

  47. What is the purpose of a NAT? What are it’s advantages and disadvantages?

  48. Explain how port numbers are used on a NAT to multiplex a single public IP address.

  49. What must be done in order to run a Web server behind a NAT?

  50. How can a NAT be used to load balance a group of identical web servers?

  51. For a given network, give the global distance-vector tables like those of the text in tables 3.10 and 3.13 when:

    a. Each node knows only the distance to its immediate neighbors.
    b. Each node has reported it had in the preceding step to its immediate neighbors.
    c. Step (b) happens a second time.
  52. Suppose P, Q, R are network service providers withrespective CIDR address allocations C1.0.0.0/8, C2.0.0.0/8, and C3.0.0.0/8. Each provider’s customers initially receive address allocations that are subsets of the provider’s. P has the following customers:
    - PA, with allocation C1.A3.0.0/16
    - PB, with allocation C1.B0.0.0/12
    Q has the following customers:
    - QA, with allocation C2.0A.10.0/20
    - QB, with allocation C2.0B.0.0/16
    Assume there are no others providers or customers.
    a. Give the routing tables for P, Q, and R assuming each provider connects to both of the others.
    b. Now assume P is connected to Q and Q is connected to R, but P and R are not directly connected. Give the tables for P and R.
    c. Suppose customer PA acquires a direct link to Q, and QA acquires a direct link to P, in addition to the existing links. Give the routing tables for P and Q, ignoring R.

  53. You are hired to design a reliable byte-stream protocol that uses a sliding window (like TCP). The protocol will run over a 1 Gbps network. The RTT of the network is 140 ms, and the maximum segment lifetime is 60 seconds. How many bits would you include in the AdvertisedWindow and SequenceNumber fields in your protocol header?

  54. Suppose, in TCP’s adaptive retransmission mechanism, that EstimatedRTT is 90 at some point and subsequent measured RTTs are all 200. How long does it take before the TimeOut value, as calculated by the Jacobson/Karels algorithm, falls below 300? Assume initial Deviation value of 25; use δ=1/8.

  55. What are the differences in the services provided by UDP and TCP? Consider reliability, connection aspects, data stream factors.

  56. Describe the differences between flow control and congestion control in general (non-protocol specific) terms.

  57. Describe the current method of that TCP uses for flow control.

  58. Describe the current methods that TCP uses for congestion control.

  59. What is a TCP segment?

  60. In TCP, what is the purpose and operation of the SequenceNumber field? How many bits is it? What is the purpose and operation of the Acknowledgementfield? How many bits is it?

  61. In TCP, what is the AdvertisedWindow field? Who is it used, and how many bits is it? What is the significance of the number of bits of this field, and how is this size a concern when considering the increasing data rates of the Internet backbone?

  62. What is the silly window syndrome, and how does Nagel’s algorithm address it?

  63. What is the purpose of Additive Increase Multiplicative Decrease? Explain how it works?

  64. What is the purpose of slow start? What issue does it address? How does it work?

  65. Describe the difference between source-based congestion avoidance and host-based congestion control. Give an example of each, and describe how these two methods work in a paragraph. Which is typical of TCP?

  66. What is the difference between fine-grained and coarse-grained approaches to QoS ? Define each.

  67. What is Symmetric Key Cipher? How, in general, does it work? What is a major limitation of this method with respect to keys, and what is a major advantage (compared to Public Key Ciphers.

  68. What is Public Key Ciphers? How, in general, does it work? Why is it used, and what is a major advantage (compared to Symmetric Key Ciphers.

  69. Security includes BOTH authentication and integrity issues. What does each of these mean?

  70. What is non-repudiation? Why is it important?

  71. Suppose a router has built up the routing table shown in the table below. The router can deliver packets directly over interfaces 0 and 1, or it can forward packets to routers R2, R3, or R4. Assume the router does the longest prefix match. Describe what the router does with a packet addressed to each of the following destinations:
    a. 128.96.171.92
    b. 128.96.167.151
    c. 128.96.163.151
    d. 128.96.169.192
    e. 128.96.165.121

    Subnet Num

    Subnet Mask

    Next Hop

    128.96.170.0

    255.255.254.0

    Interface 0

    128.96.168.0

    255.255.254.0

    Interface 1

    128.96.166.0

    255.255.254.0

    R2

    128.96.164.0

    255.255.252.0

    R3

    (default)

    R4

Topic revision: r1 - 2015-12-02 - JimSkon
 
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