Problems Pcc
1. Identify the address class of the following IP addresses: 200.58.20.165; 128.167.23.20; 16.196.128.50; 150.156.10.10; 250.10.24.96.
2. Identify the range of IPv4 addresses spanned by Class A, Class B, and Class C.
3. A university has 150 LANs with 100 hosts in each LAN.
a. Suppose the university has one Class B address. Design an appropriate subnet addressing scheme.
b. Design an appropriate CIDR addressing scheme.
4. A small organization has a Class C address for seven networks each with 24 hosts. What is an appropriate subnet mask?
5. A packet with IP address 150.100.12.55 arrives at router R1 in Figure 8.7. Explain how the packet is delivered to the appropriate host.
6. In Figure 8.7 assign a physical layer address 1,2, ... to each physical interface starting from the top row, moving right to left, and then moving down. Suppose H4 sends an IP packet to H1. Show the sequence of IP packets and Ethernet frames exchanged to accomplish this transfer.
7. ARP is used to find the MAC address that corresponds to an IP address; RARP is used to find the IP address that corresponds to a MAC address. True or false?
8. Perform CIDR aggregation on the following/24 IP addresses: 128.56.24.0/24; 128.56.25.0/ 24; 128.56.26.0/24; 128.56.27.0/24.
9. Perform CIDR aggregation on the following /24 IP addresses: 200.96.86.0/24; 200.96.87.0/ 24; 200.96.88.0/24; 200.96.89.0/24.
10. The following are estimates of the population of major regions of the world: Africa 900 million; South America 500 million; North America 400 million; East Asia 1500 million; South and Central Asia 2200 million; Russia 200 million; Europe 500 million.
a. Suppose each region is to be assigned 100 IP addresses per person. Is this possible? If not, how many addresses can be assigned per person.
b. Design an appropriate CIDR scheme to provide the addressing in part (a).
11. Suppose four major ISPs were to emerge with points of presence in every major region of the world. How should a CIDR scheme treat these ISPs in relation to addressing for each major region?
12. Suppose that a Teledesic-like satellite network (Chapter 4) is based on IP routing. Design a CIDR scheme assuming each cell has 100,000 hosts.
13. Look up the netstat command in the manual for your system. Find and try the command to display the routing table in your host.
14. Suppose a router receives an IP packet containing 600 data bytes and has to forward the packet to a network with maximum transmission unit of 200 bytes. Assume that IP header is 20 bytes long. Show the fragments that the router creates and specify the relevant values in each fragment header (i.e., total length, fragment offset, and more bit).
15. Design an algorithm for reassembling fragments of an IP packet at the destination IP.
16. Does it make sense to do reassembly at intermediate routers? Explain.
17. Abbreviate the following IPv6 addresses:
a. 0000:0000:0F53:6382:AB00:67DB:BB27:7332
b. 0000:0000:0000:0000:0000:0000:004D:ABCD
c. 0000:0000:0000:AF36:7328:0000:87AA:0398
d. 2819:00AF:0000:0000:0000:0035:0CB2:B2 71
18. What is the efficiency of IPv6 packets that carry 10 ms of 64 kbps voice? Repeat if an IPv6 packets carries 1 frame of 4 Mbps MPEG2 video, assuming 30 frames/second.
19. Why does IPv6 allow fragmentation at the source only?
20. Assuming the population estimates in problem 10, how many IP addresses does IPv6 provide per capita?
21. Suppose that IPv6 is used over a noisy wireless link. What is the effect of not having header error checking?
22. Explain how the use of hierarchy enhances scalability in the following aspects of Internet:
a. Domain name system b. IP addressing c. OSPF routing d. Interdomain routing
23. The TCP in station A sends a SYN segment with ISN = 1000 and MSS = 1000 to station B. Station B replies with a SYN segment with ISN = 5000 and MSS = 500. Suppose station A has 10,000 bytes to transfer to B. Assume the link between stations A and B
is 8 Mbps and the distance between them is 200 m. Neglect the header overheads to keep the arithmetic simple. Station B has 3000 bytes of buffer available to receive data from A. Sketch the sequence of segment exchanges, including the parameter values in the segment headers, and the state as a function of time at the two stations under the following situations:
a. Station A sends its first data segment at t = 0. Station B has no data to send and sends an ACK segment every other frame.
b. Station A sends its first data segment at t = 0. Station B has 6000 bytes to send and sends its first data segment at t = 2 ms.
24. Suppose that the TCP in station A sends information to the TCP in station B over a two-hop path. The data link in the first hop operates at a speed of 8 Mbps, and the data link in the second hop operates at a speed of 400 kbps. Station B has a 3 kilobyte buffer to receive information from A, and the application at station B reads information from the receive buffer at a rate of 800 kbps. The TCP in station A sends a SYN segment with ISN = 1000 and MSS = 1000 to station B. Station B replies with a SYN segment with ISN = 5000 and MSS = 500. Suppose station A has 10,000 bytes to transfer to B. Neglect the header overheads to keep the arithmetic simple. Sketch the sequence of segment exchanges, including the parameter values in the segment headers, and the state as a function of time at the two stations. Show the contents of the buffers in the intermediate switch as well as at the source and destination stations.
25. Suppose that the delays experienced by segments traversing the network are equally likely to be any value in the interval [50 ms, 75 ms].
a. Find the mean and standard deviation of the delay.
b. Most computer languages have a function for generating uniformly distributed random variables. Use this function in a short program to generate random times in the above interval. Also, calculate tRTT and dRTT and compare to part (a).
26. Suppose that the advertised window is 1 Mbyte long. If a sequence number is selected at random from the entire sequence number space, what is the probability that the sequence number falls inside the advertised window?
27. Explain the relationship between advertised window size, RTT, delay-bandwidth product, and the maximum achievable throughput in TCP.
a. Plot the maximum achievable throughput versus delay-bandwidth product for an advertised window size of 65,535 bytes.
b. In the preceding plot include the maximum achievable throughput when the window size is scaled up by a factor of 2K, where K = 4, 8, 12.
c. Place the following scenarios in the plot obtained in part (b): Ethernet with 1 Gbps and distance 100 meters; 2.4 Gbps and distance of 6000 km; satellite link with speed of 45 Mbps and RTT of 500 ms; 40 Gbps link with distance of 6000 km.
28. Consider the three-way handshake in TCP connection setup.
a. Suppose that an old SYN segment from station A arrives at station B, requesting aTCP connection. Explain how the three-way handshake procedure ensures that the connection is rejected.
b. Now suppose that an old SYN segment from station A arrives at station B, followed a bit later by an old ACK segment from A to a SYN segment from B. Is this connection request also rejected?
29. Suppose that the initial sequence number (ISN) for a TCP connection is selected by taking the 32 low-order bits from a local clock.
a. Plot the ISN versus time assuming that the clock ticks forward once every 1/Rc seconds. Extend the plot so that the sequence numbers wrap around.
b. To prevent old segments from disrupting a new connection, we forbid sequence numbers that fall in the range corresponding to 2MSL seconds prior to their use as an ISN. Show the range of forbidden sequence numbers versus time in the plot from part (a).
c. Suppose that the transmitter sends bytes at an average rate R > Rc. Use the plot from part (b) to show what goes wrong.
d. Now suppose that the connection is long-lived and that bytes are transmitted at a rate R that is much lower than Rc. Use the plot from part (b) to show what goes wrong. What can the transmitter do when it sees that this problem is about to happen?
30. Suppose that during the TCP connection closing procedure, a machine that is in the TIME_WAIT state crashes, reboots within MSL seconds and immediately attempts to reestablish the connection, using the same port numbers. Give an example that shows that delayed segments from the previous connections can cause problems. For this reason RFC 793 requires that for MSL seconds after rebooting TCP is not allowed to establish new connections.
31. Are there any problems if the server in a TCP connection initiates an active close?
32. A fast typist can do 100 words a minute, and each word has an average of six characters. Demonstrate Nagle's algorithm by showing the sequence of TCP segment exchanges between a client, with input from our fast typist, and a server. Indicate how many characters are contained in each segment sent from the client. Consider the following two cases:
a. The client and server are in the same LAN and the RTT is 20 ms.
b. The client and server are connected across a WAN and the RTT is 100 ms.
33. Simultaneous Open. The TCP state transition diagram allows for the case where the two stations issue a SYN segment at nearly the same time. Draw the sequence of segment exchanges and use Figure 8.28 to show the sequence of states that are followed by the two stations in this case.
34. Simultaneous Close. The TCP state transition diagram allows for the case where the two stations issue a FIN segment at nearly the same time. Draw the sequence of segment exchanges and use Figure 8.28 to show the sequence of states that are followed by the two stations in this case.
35. Suppose an ISP has 1000 customers and that at any time during the busiest hour of the day the probability that a particular user requires service is 20. The ISP uses DHCP. Is a Class C address enough to make the probability less than 1 percent that no IP address is available when a customer places a request?
36. Compare mobile IP with the procedures used by cellular telephone networks (Chapter 4) to handle roaming users.
a. Which cellular network components provide the functions of the home and foreign agent?
b. Is the handling of mobility affected by whether the transfer service is connectionless or connection oriented?
37. Consider a user that can be in several places (home networks) at different times. Suppose that the home networks of a user contain registration servers where users send updates of their location at a given time.
a. Explain how a client process in a given end system can find the location of a given user to establish a connection, for example, Internet telephone, at a given point in time.
b. Suppose that proxy servers are available, and their function is to redirect location requests to another server that has more precise location information about the callee. For example, a university might have such a server, which redirects requests for prof@university.edu to departmental servers. Explain how a location request for engineer@home.com might be redirected to a.prof@ece.university.edu.
38. What is the maximum width of an RIP network?
39. Let's consider the bandwidth consumption of the RIP protocol.
a. Estimate the number of messages exchanged per unit time by RIP.
b. Estimate the size of the messages exchanged as a function of the size of the RIP network.
c. Estimate the bandwidth consumption of an RIP network.
40. RIP runs over UDP, OSPF runs over IP, and BGP runs over TCP. Compare the merits of operating a routing protocol over TCP, UDP, IP.
41. Compare RIP and OSPF with respect to convergence time and the number messages exchanged under several trigger conditions, that is, link failure, node failure, and link coming up.
42. Consider the OSPF protocol.
a. Explain how OSPF operates in an autonomous system that has no defined areas.
b. Explain how the notion of area reduces the amount of routing traffic exchanged.
c. Is the notion of area related to subnetting? Explain. What happens if all addresses in an area have the same prefix.
43. Assume that there are N routers in the network and that every router has m neighbors.
a. Estimate the amount of memory required to store the information used by the distance-vector routing.
b. Estimate the amount of money required to store the information by the link-state algorithm.
44. Suppose a network uses distance-vector routing. What happens if the router sends a distance vector with all Os?
45. Suppose a network uses link-state routing. Explain what happens if:
a. The router fails to claim a link that is attached to it.
b. The router claims to have a link that does not exist.
46. Consider a broadcast network that has n OSPF routers.
a. Estimate the number of database exchanges required to synchronize routing databases.
b. What is the number of database exchanges after a designated router is introduced into the network?
c. Why is the backup designated router introduced? What is the resulting number of database exchanges?
47. Suppose n OSPF routers are connected to a nonbroadcast multiaccess network, for example, ATM.
a. How many virtual circuits are necessary to provide the required full connectivity?
b. Does OSPF function correctly if a virtual circuit fails?
c. Is the number of required virtual circuits reduced if point-to-multipoint virtual circuits are available?
48. The figure below shows seven routers connected with links that have the indicated costs. Use the Hello protocol to show how the routers develop the same topology database for the network.
49. Consider the exchange of Hello messages in OSPF.
a. Estimate the number of Hello messages exchanged per unit time.
b. Estimate the size of the Hello messages.
c. Estimate the bandwidth consumed by Hello messages.
50. Consider the notion of adjacency in OSPF.
a. Explain why it is essential that all adjacent routers be synchronized.
b. Explain why it is sufficient that all adjacent routers be synchronized; that is, it is not necessary that all pairs of routers be synchronized.
51. Consider the robustness of OSPF.
a. Explain how the LSA checksum provides robustness in the OSPF protocol.
b. An OSPF router increments the LS Age each time the router inserts the LSA into a link-state update packet. Explain how this step protects against an LSA that is caught in a loop.
c. OSPF defines a minimum LS update interval of 5 seconds. Explain why.
52. Assume that for OSPF updates occur every 30 minutes, an update packet can carry three LSAs, and each LSA is 36 bytes long. Estimate the bandwidth used in advertising one LSA.
53. Identify elements where OSPF and BGP are similar and elements where they differ. Explain the reasons for similarity and difference.
54. Discuss the OSPF alternate routing capability for the following cases:
a. Traffic engineering, that is, the control of traffic flows in the network.
b. QoS routing, that is, the identification of paths that meet certain QoS requirements.
c. Cost-sensitive routing, that is, the identification of paths that meet certain price constraints.
d. Differential security routing, that is, the identification of paths that provide different levels of security.
55. Consider the following arrangement of autonomous systems and BGP routers.
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