CMPS 284 Final, Fall 2004

Faculty of Arts & Sciences AMERICAN UNIVERSIF Department of Computer Science LIBRARY CMPS 284—Computer Networks ee Fall 2004-2005 Monday, January 24, 2005 7 Final Exam “* Version 3 Name: Student Id: Signature: Section: Section I MWF 8:00 — 8:50 Duration: 120 minutes Section Il | MwF 9:00 - 9:50 Instructions ¢ There are 6 problems and 12 pages. Make sure you have all of them. ¢ The exam is closed book, closed notes, closed calculators, and closed neighbors. * Answer questions in the space provided. The questions not sorted by difficulty. Scan the whole exam before you start working. Your handwriting should be readable so it can be graded. Include all work or justification for partial credit. Probiem 1 Problem 2 Problem 3 Problem 4 Problem 5 Problem 6 Final Exam (2005-01-24) Initials: Problem 1 [7 points] Show how the routing table of F is formed by a starting from node F. CMPS 284 Final Exam (2005-01-24) Initials: Problem 2-[20 points] Answer the following questions. Make your answer as short as possible as you will not get credit for long answers. 1. TCP uses the packet (or datagram) delivery service provided by IP, which allows the possibility that IP packets can be dropped (ie. not delivered). How does the TCP software cope if this happens? Note that detailed description is not required here, just an outline of the basic ideas involved. [3points] 2. An IP datagram has a header field called Time To Live (TTL) which is decremented each time the datagram crosses a router. Why is this done and what happens if it ever reaches zero? [2 points| 3. How does TCP control and reduce the network congestion? [3 points] 4. What does POP stand for? [1 point] 5. What the main task of POP? [1 point} CMPS 284 Final Exam (2005-01-24) Initials: In assignment 3, you had to develop a UDP client server application. The client had to successfully register with the server before getting access to the cash register. Sketch the flowchart for an UDP/IP client-server application (it is enough to just provide the main system calls). In this flowchart, illustrate when and how the client sends a register message to the server and how the server reacts to this message. [6 points] SERVER CLIENT CMPS 284 Final Exam (2005-01-24} Initials: 7. traceroute is a network tool that is used to construct a list of all routers along a path from a source computer to a given destination. Explain how traceroute uses ICMP messages to do so? [4 points] CMPS 284 Final Exam (2005-01-24) initials: Problem 3-[30 points] Suppose that a corporate has a class C network with network ID 194.80.40.0. The corporate comprises three departments but expected to grow to 5 departments in a year. Currentiy each department has less than five employees but the number of employees in each department expected to rise to 20 in a year. The network administrator was asked to create a separate subnetwork for each department. To cop with the expected grow the administrator used 3 bits for the subnet id and 5 bits for the host id. t. What is the dotted decimal representation of the mask address of class C networks?[1 point] What is the dotted decimal representation of the subnet mask address in the network mentioned above? [point] How many subnets can be supported in the network design mentioned above? [1 point] What is the maximum number of hosts per subnet in the network design mentioned above? [1 point] Assume that the network administrator created three different subnetworks to support the corporate three existing departments as shown in the diagram below. The subnet A was assigned the subnet id 194.80.40.32. Subnet B Bl B2 Subnet A 194.80.40.32 Subnet C 5.1. Looking at the subnet id of subnet A, assign the next available subnet ids to subnet B and subnet C. What are the values of these ids in dotted decimal? | 2 points] CMPS 284 Final Exam (2005-01-24) Initials: 5.2. For each subnet provide the following:[4.5 points] Lowest IP address that can i Lowest IP address that can be Broadcast IP address be assigned to a host |_assigned to a host 5.3. Write down an IP address for each interface at all hosts and routers in the diagram. In each subnetwork, for hosts, start from the lowest possible address and up. For routers, use the highest possible IP address and down.|6 points] Subnet A 5.4, Given your IP addresses from above, what are the contents of the routing table of router R1 (include Destination Network, Mask Address, and Next Hop).[4.5 points} Destination Subnet | Subnet Mask Next hop CMPS 284 "Final Exam (2005-01-24) Initials: 5.5. Suppose that al, a2 and a3 are the hardware addresses for hosts Al, A2, and A3 respectively; bl and b2 are the hardware addresses for hosts B1 and B2 respectively; cl. c2 and c3 are the hardware addresses for hosts C1, C2, and AC respectively; il, i2, 13, i4 are the hardware addresses for the interfaces 11, 12, 13, 14 at routers RI and R2. Give the ARP table for station Al assuming that Al has recently communicated with all other stations. [3 points] IP Address Hardware Address 5.6. If Al sends B] an IP packet, explain what takes place at Net A and Net B by sketching the headers (namely the address fields) for a packet as it flows from host A} to host Bi [2 points]. CMPS 284 8 of 12 Initials: Final Exam (2005-01-24) 6. Consider sending an IP packet of 3000 bytes into a link that has an MTU size of 500 bytes. Suppose that the original datagram is stamped with the identification number 422. How many fragments are generated? What are the values of the offset and identification fields of each fragment? [4 points] CMPS 284 Final Exam (2005-01-24) Initials: Problem 4-[16 points] Matching - choose (from among the choices listed below) the word/phrase that best matches each statement. Physical Layer TCP/IP Relay Agent UDP ARP Loopback addess RARP FIN LAN WAN Network Layer End-to-End Checksum ACK SYN Packet Switches ICMP packet loss Flow Control Hop-by-Hop Port number Ipv4Address OSI] Dijkstra DNS Bridge LinkState Router Transport Layer Switch Out of order delivery Encapsulation Resolver Datalink Layer Socket 1. Internet layer protocol that can be used by IP to send control information. 2. Application client that is used to translate a name to an JP address. 3. Programmer uses for testing and preliminary debugging network applications. 4, Interconnects networks that use different technologies, including different physica! addressing and different frame formats. 5. Fundamental building blocks of a WAN include and high-speed connections between them. 6. Provides communication between processes running on end-systems on possibly different networks. 7, Forwards DHCP messages between clients and servers. 8. In general, reliability protects against and 9. 32 Bit identifier used to route IP datagrams. 10. 16 bit identifier used to deliver TCP segments and UDP datagrams to the correct process. 11. A widely used protocol suite. 12. Used to translate an Ethernet Address to IP address. 13. Often used for error detection. 14. A transport layer protocol. 15. One of the main routing schemes. CMPS 284 10 of 12