ASSIGNMENT 2 Computer Networks

This assignment comprises of 4 questions worth 25 marks each, based on the work you have completed in the Networking laboratory exercises. Some questions may also require you to carry out further research to give complete answers. Insert annotated printouts of protocol decode traces, flow graphs or other diagrams (as required) clearly indicating which question they refer to. Full marks will be awarded for answering all 4 questions.

Submit at Reception by 10am 1st May 2013 PROVISIONAL

1. This question relates to lab1: ‘Lab intro and Ethernet LAN’.

(a) (i) State the MAC address (in hex) of the network card you used in the lab exercises

and identify the significance of the left-most three bytes.

(ii) With the aid of a diagram distinguish between Ethernet II and IEEE 802.3 frames.

(iii) Summarise the meaning of the physical interface designation 10/1001000BASET of the Intel Pro interface cards you used in the lab programme.

(iv) State the command (entered at the command line of a Windows 7 workstation) that will map a local drive z: to a share called utils on a computer called Server 1

(8 marks)

(b) (i) Draw in the links necessary to connect the four hubs shown in Figure Q1b via a central switch if only 3 straight through UTP cables are available and one crossover cable - the switch does not have a crossover port or auto cable sensing.

(ii) State the two main functions of a switching hub (Ethernet switch) and explain what might happen if you connect a crossover cable between two ports on a non IEEE 802.1d compliant switch:

(iii) Submit a screenshot of the Packet Tracer simulation of the switch LAN showing a unicast packet sent between PC0 and PC2 including OSI layer functions. (9 marks)

(c) (i) Figure Q1c shows the packets captured with Wireshark when a host computer was Pinged by its NetBIOS name. Explain the purpose of the first 4 packets.

(ii) Distinguish between unicast transmission as used by the ICMP packets and broadcasts used by ARP the packets

(iii) Explain why playing multiple unicast DVD video streams across the 10BASET LAN

caused playback problems, but didn't when the broadcast stream was played.

Figure Q1c (8 marks)

2. This question relates to lab2: ‘Introduction to IEEE 802.11 Wireless LANs’

(a) (i) Submit the Table of results from part A showing the wireless networks detected with the InSSider site survey tool.

You will need to assume Noise level is -100dBm in order to calculate the S/N ratio.

(ii) Define the RSSI and S/N metrics used in th e Table

(iii) Calculate the power level in nW received by your network adapter and the noise level in dBm for a RSSI of -60dBm and S/N of 30dB.

(iv) Figure Q2a shows the radio spectrum during the period when the video sender was active in the lab. Analyse the spectrum and then discuss the effects of the sender on WLAN operation. Suggest how the video sender interference could be minimised for 802.11b/g mode and why a 802.11a network might be a better choice in the presence this type of interference.

Figure Q2a

(10 marks)

(b) Figure Q2b shows the lab layout diagram for lab tests and assumes both APs have same SSID.

Figure Q2b

Explain the network operation and the function of the APs when:

(i) PCs A and B, associated with WAP1 BSS, communicate with each other.

(ii) PC A, associated with WAP1s BSS, communicates with a PC C associated with WAP2's BSS.

(iii) PC D sends a broadcast message (5 marks

(c) (i) Explain why your data throughput results were much lower than the raw transmission speed of 54 Mbps. Also account for the better throughput between

wireless station and wired server compared to wireless to wireless station

(ii) List the enhancements that improve the performance of IEEE 802.11n WLANs.

(iii) Determine the maximum raw transmission speed you would expect from the IEEE 802.11n Cisco.AP54n access points and TPLink network cards used in the lab.

(iv) Explain why security is more of a problem for IEEE 802.11 Wireless Networks than IEEE 802.3 wired networks and the reasons that WEP, MAC filtering and ssid cloaking are considered ineffective security measures.

(10 marks)

3. This question relates to lab3: ‘Introduction to TCP/IP and Static Routing’

(a) (i) Submit a Packet Tracer 3.2 simulation diagram for the 3 subnet network of Figure3a including a display of the connected and static routes in the routing tables for full subnet connectivity.

Figure Q3a

(ii) Explain why Ping Echo replies from the printer could only be received by PCs on Subnet 1 and what configuration change would be necessary to reach subnet 2 PCs.

(iii) Explain with the aid of a diagram the extra configuration necessary to give clients on each subnet access to the Internet.

(8 marks)

(b) (i) Which TCP/IP utility on a Windows 7 PC is used to:

View the complete IP configuration

View the NetBIOS name cache

Clear the ARP cache

(ii) Explain how Tracert works and what it is used for.

(iii) Explain the purpose of the following router table entries:

Interface address 127.0.0.1

Network destination 0.0.0.0

Net Mask 255.255.255.0

Network destination 192.168.1.255

Network destination 224.0.0.0

(6 marks)

(c) (i) Submit a printout of the first Ping packet you captured with Wireshark when your PC successfully PINGed a remote subnet PC.

Highlight on the printout the MAC and IP addresses of destination and source PC and the ICMP packet type/code.

(ii) Explain why the destination MAC address is not the same as the MAC address of the PC that actually sent the ICMP Packet. (5 marks)

(d) (i) A single Class C network 192.168.10.0 needs to be divided into four RFC950 compliant subnets. Determine the following:

Subnet Mask

The subnet number

Range of addresses for each subnet

(ii) Submit a printout of the relevant packets that you captured with Wireshark showing the four phases of DHCP. Explain briefly the function of each phase with reference to the derived flowgraph.

(6 marks)

4. This question relates to lab4: ‘Intro to Dynamic Routing and Name Resolution’

(a) (i) Submit Table 2 with the entries completed for your subnet Router.

(ii) Distinguish between RIPv1 and RIPv2 dynamic Routing protocols.

(iii) Submit the printout of a RIP v1 packet you captured with Wireshark showing the announced routes after the network had fully converged - highlight the section which shows the routes and determine the time between RIP packet updates.

(8 marks)

(b) Figure Q4 summarises access to the Internet from a PC on the RIP routed lab intranet. All the lab routers have RIP v1 dynamic routing installed and complete routing tables, but the ADSL Router doesn’t support RIP

(i) Determine the default gateway setting for Routerx and Router6 to allow your PC to reach the Internet.

(ii) Determine the static route entries for the ADSL Router and any other TCP/IP configuration necessary for successful Ping tests to the web server address shown.

Figure Q4

(iii) Simulate the RIP loop network of Part 7 and include the routing tables for each router of the fully converged network when the link between subnet 2 and 3 is down.

(8 marks)

(c) (i) Explain why, in Part1, PCs were not able to ping PCs on other subnets using their NetBIOS names, but could do so by their IP address.

(ii) Explain how the hosts file was used to solve the problem of c (i). Illustrate with an extract from the file you created in the lab.

(iii) Submit the displayed results and the contents of the question and answer records of the packets captured when you performed an NSLOOKUP of the FQDN of one of the lab PCs.

(iv) Describe the TCP/IP configuration changes required to your PC and DNS server in order allow access to the private intranet PCs and Internet hosts by FQDNs.

(9 marks)