Data Communications and Network - Assignment Example

Data Communications and Network Student’s Name Institution Date Question 1 (22 marks) – Transport Layer a. As we have seen, the Internet layer of TCP/IP has two protocols – IPv4 and IPv6. The transport layer provides two main protocols TCP and UDP (along with some special-purpose, minor protocols). But these are for very different reasons. Why are the Internet and Transport layers very different in providing two protocols? (8 marks) The TCP/IP network or more generally the internet provides two distinct transport layer protocols available to the application layer. The two protocols are UDP and TCP. UDP, or User Datagram Protocol provides a connectionless service available to the invoking application. The other protocol which is the Transmission Control Protocol (TCP) provides a more reliable, connection-oriented service to the requesting service (Li and Wang, 2015). One of this protocols have to be specified by an application developer in the design of a network application and specifically during the creation of sockets. The internet and the transport layers are different in the provision of protocols in that the internet protocol (IP) addressing scheme is hierarchical in nature and therefore very scalable. It provides an end-node verification feature and also supports dynamic routing and this two features contribute to its decentralization. A domain name server (DNS) is tasked with the responsibility of mapping domain names to IP addresses. The IP addresses are the unique identifying markers of all the devices connected to a network. The devices in the network receive data using ports which are logical channels used for routing data to the required network application. The transport layer of a network is responsible for providing error checking, flow control of data packets and acknowledgement services thus promoting a reliable data transfer service. These services are achieved through the use of flow control, acknowledgements and sequence numbers and timers. The TCP is responsible for ensure that sent and received data is done in the correct order through breaking the sent message into segments that are then assigned sequence numbers based on the correct order from the sender (source machine). The segments are dispatched using IP packets and may take different routes to the destination where they may arrive out of sequence (Mbale and Mufeti, 2011). The assigned sequence numbers are used to rearrange the packets in the correct order. As such the internet and the transport layers provide different protocols to support the mode and type of data to be transmitted. a) Since UDP does very little that is different from IP, why do we even have a transport layer such as UDP? (7 marks) The User Datagram Protocol (UDP) provides a connectionless service that delivers packets quickly. However, in the event that some of the packets are lost, UDP does not guarantee retransmission of those packets. There is little difference between what UDP offers compared to what is offered by the IP protocol. However, there are some underlying reasons why this protocol is still prevalent and has not been faced out. Among them include the fact that it does not need any connection setup since it does not need to retransmit the lost packets. Therefore, it is fast compared to TCP/IP and less delay is incurred sending the data. Some applications such as audio and video are delay sensitive and this makes UDP popular among this applications. Besides, the degree of some packet loss can be tolerated in voice and video as opposed to other applications. Also, applications dependent on multicast are built on top of the UDP in order to point to the multipoint (Wu, n.d.). TCP would not be applicable in such applications since the sender would be required to track the retransmissions from multiple servers which is not applicable in UDP. Also, UDP does not restrict the user on the connection based communication model to be used since the operating system is not required to maintain the connection information of UDP. Since the packets do not undergo verification as required in TCP, less processing is done at the receiving and transmitting hosts. With the increased use of time sensitive applications in modern life such as voice and video, UDP continues to be a viable choice due to its ability to be time sensitive. b) Describe how DDoS attacks may be mounted against TCP and UDP services. In what way will being connection oriented be different for TCP and UDP? (7 marks) DDoS refers to denial of service attacks that are a prevalent in internet applications. For TCP, in order to setup a connection, a 3 way handshake is required. Attackers realize this and they often use spoofing attacks based on IP addresses to perpetrate a denial of service attack. In a TCP oriented service, several IP addresses are spoofed simultaneously and continuously sending multiple requests to the domain name server which it is unable to meet the processing demands of the requests. On the other hand, UDP faces a SYN flood style of attack where the attacker overwhelms random ports on the host server containing the UDP datagrams (Kalajdzic, Patel and Taghavi, 2011). The receiving host often checks for datagrams on the serve and finds none and instead receives a destination unreachable packet and with the increased attack the system becomes unresponsive to other clients. Since TCP is connection oriented, the attacker holds to the spoofed IP making the server unreachable while for UDP since it is connectionless, it becomes unresponsive due to the multiple attacks. Question 2 (22 marks) – IP Addressing a) Perform the following Boolean operations on the given bit patterns (3 marks) i. not 11100010 000111101 ii. 11100010 or 00001110 11101110 iii. 11100010 and 00001110 00000010 b) What are the subnet masks for the following slash address blocks? (3 marks) i. /9 255.128.0.0 ii. /17 255.255.128.0 iii. /31 255.255.255.254 c) Are the following address masks legal? If so, what are their slash forms? If not, why are they not legal? (4 marks) i. 255.255.248.0 Valid with the following slash notation 2¹¹ or /21 ii. 255.224.252.0 Illegal iii. 255.255.255.224 Valid with the following slash form 2⁵ or /27 iv. 255.255.156.0 Illegal d) How many computers are in networks with the following address blocks? (2 marks) i. /13 2¹⁹ 524,288 or 512 k computers ii. /26 26 64 computers e) A small company is assigned the class C network 205.67.35.0. You need to divide this network to provide subnets for three departments using fixed-length subnetting. The departments are approximately the same size. Show the network and broadcast addresses for each subnet. Show the slash notation. How many hosts are on each subnet? Are the resulting subnets class C networks? (10 marks) Network class C subnetted as class C with a subnet mask of 255.255.255.192 or /26 There are 4 subnets and 64 nodes or host per network that include network and broadcast addresses. List of Networks For the 205.67.35.0 network with the subnet mask 255.255.255.192 Network Hosts Broadcast Address from to 205.67.35.0 205.67.35.1 205.67.35.62 205.67.35.63 205.67.35.64 205.67.35.65 205.67.35.126 205.67.35.127 205.67.35.128 205.67.35.129 205.67.35.190 205.67.35.191 205.67.35.192 205.67.35.193 205.67.35.254 205.67.35.255 Question 3 (20 marks) – Wireless a. Explain why CSMA/CD scheme used in traditional Ethernet LANs cannot be used in 802.11 wireless LANs. (5 marks) The CSMA/CD refers to collision. On a traditional Ethernet LAN using coaxial cables, transmission occurs on multiple transceivers in the same cable if the cable is idle and it can monitor the cable while transmitting. The waveform in the cable must match what the transmitter is sending else there is an active transmission and this leads to collision. It works on traditional Ethernet LANs such as copper cable since signal levels remain constant along the cable length. The signal level is only reduced by the cable impedance (Harrington, 2007). For wireless LANs, it is not possible to monitor to monitor other transmissions when the transmitter is sending. Thus, CSMA/CD used in traditional Ethernet LANs cannot be used in 802.11 wireless LANs. In a wireless LAN, signals spread in three special coordinate vectors and the signal attenuation is based on the square of the travelled distance. Besides, in wireless LANs, it is impossible to exclude reflections from external objects such as wall and metal objects within the transceivers range (Harrington, 2007). b. A supermarket uses WiFi to enable staff to check inventory levels and to perform price checks. Staff have complained that the wireless scanners they use to check stock levels do not work reliably in some isles. The supermarket manager has contracted you to diagnose the wireless problems and correct them. The supermarket is 60m by 40m. Assume that the useful range of WiFi within the warehouse will be 15m radius. The access points are organized into a grid with the following channel allocations: i. You have determined that the channel allocations are not optimal, how would you improve upon the current channel allocations? (10 marks) To enhance accessibility and reduce the challenges that the supermarket is currently facing, it is essential to first identify the configuration mistakes made in the installations of the access points. In this case, the current channel allocation can be improved through proper placement to avoid interference. Since the room is 60 by 40 meters, the square meters is 2400. However, one WiFi access point has a reach of 15M in radius which means it covers an area of 706.86 meters.to determine the number of access points required, we divide the entire area with the coverage of one access point. Thus, to cover 2400 meters, 3.4 access point are required. Therefore, we can use 3 Ch6 access point and an extra Ch1 access point reducing the initial number by two which is economical for the supermarket. Besides, to ensure that the entire area becomes a hotspot, the access point can be placed in the ceiling as it will reduce interference and obstruction from HVAC ducts, metal fixtures and utility pipes thus ensuring that the RF signal is not negatively affected and this increased the wireless signal performance. ii. As you are reconfiguring the access points you notice that none of them currently have any security enabled. Is this a problem, and if so, what type of security would you recommend? (5 marks) This being a supermarket, majority of the people are customers who do not stay for long and hence the probability of using the supermarkets network is relatively low. However, every network requires some level of security and since sensitive data such as credit card information used to make payments is transmitted through this network, it is critical to ensure the network is safe (Li and Wang, 2015). The network is shared among the employees and therefore, using a WiFi protected access using usernames and passwords only made available to the employees is essential. It is also recommended to encrypt data shared within the network to protect from eavesdropping attacks. It is also recommended that access levels be restricted in the network based on the users’ level and tasks being performed. Lastly, to ensure proper security, it is inherent to ensure the constant password changes for security reasons. List of References Harrington, J. (2007). Ethernet networking for the small office and professional home office. 1st ed. Amsterdam: Morgan Kaufmann Publishers/Elsevier. Kalajdzic, K., Patel, A. and Taghavi, M. (2011). Two Methods for Active Detection and Prevention of Sophisticated ARP-Poisoning Man-in-the-Middle Attacks on Switched Ethernet LANs. International Journal of Digital Crime and Forensics, 3(3), pp.50-60. Li, M. and Wang, X. (2015). Delay and rate satisfaction for data transmission with application in wireless communications. IEEE Network, 29(5), pp.70-75. Mbale, J. and Mufeti, K. (2011). Phase teaching model for subnetting IPv4. International Journal of Internet Technology and Secured Transactions, 3(1), p.1. Wu, C. (n.d.). On network-layer packet traceback: Tracing denial-of-service (DoS) and distributed denial-of-service (DDoS) attacks. 1st ed. Read More