Computer Networks Answers

TCP

Open the “tcp_packet_capture” trace file and find the first HTTP GET message from the trace with

packet length equal to 517 bytes and sequence number 2398008939. Hint: To limit yourself to TCP

messages, enter the string tcp in the filter field and then apply the filter. Answer the following

questions:

a. What are the IP address and TCP port number used by the client computer to retrieve

the file? [1]

b. What is the next sequence number of the TCP SYN segment? (Give the relative sequence

number). [2]

c. What is the flag field set to? [1]

d. Based on the value of the fields what flags are set in this TCP message?

UDP

Open the “udp_packet_capture” trace file and select the first DNS query packet from the trace. Hint: To limit yourself to DNS packets, enter the string DNS in the filter field and then apply the filter.

a. By consulting the displayed information in Wireshark’s packet content field for this packet, determine the length in bytes of each of the UDP header fields.

b. By examining the UDP header explain whether or not UDP can provide reliability.

c. What is the maximum number of bytes that can be included in a UDP payload?

d. What is the protocol number (in hex) for UDP?

e. What is the source port number for the query?

f. What is the destination port number for the response? 

HTTP

Open the “tcp_packet_capture” file and select the HTTP get message from the trace with Sequence Number: 3559289491. Hint: To limit yourself to http packets, enter the string http in the filter field and then apply the filter. To get the actual sequence number instead of the relative sequence number, right click go to protocol preferences and make sure the relative sequence numbers option is not selected.

a. What is the IP address of the machine that generated the HTTP request? [1]

b. What is the IP address of the server that will handle this request? [1]

c. Does the client request a persistent connection? [1]

d. How do you know? [1]

e. What operating system was this request sent from? [1]  

Horizontal cabling in a structured cabling system connects the telecommunications room to the work areas on the buildings. This method of cabling is typically installed when the building is being initially assembled. Horizontal cabling is normally an unshielded twisted-pair cable or UTP. Some Special standards or principles regulate how long the cables should be installed in the building and where the horizontal cabling should be mounted to prevent electromagnetic interference. This kind of cabling is like “last mile” cabling before reaching a computer in a work area. Various components such as mechanical terminations, jumpers and patch cords located in the Telecommunication room are also involved. With the aid of a diagram, illustrate how horizontal cabling systems get connected from the telecommunications room to the work areas in the buildings. In your illustration, ensure you indicate various details that need to be involved, such as meters, etc.

You are a Technology Specialist in your organisation. You have been tasked to run a workshop on network system design specifically looking into the requirements and constraints. You have decided to approach the task by studying the components that make up a network system and then the relationship between network systems and related areas. Thus far, you have realised that you will base your workshop on the exhibit extracted from Serpanos and Wolf (2011). Exhibit: Requirements and constraints for network system design 

Identify a suitable network scenario/case that can be used to explain and discuss the relationship of concepts in the exhibit. Ensure that you provide details of the following aspects of the scenario: • Description of the scenario; • Why the scenario is considered a network system.

The following are noted about the institution:

• The tertiary institution consists of the Head Office in Cape Town and one campus each in Durban, Johannesburg and Cape Town.

• Each campus consists of:

o Four lecturing halls;

o A library;

o Four computer/electronic device facilities; o IT Support office.

• All client computers run Windows 7 or latest operating system, Microsoft Office 2013 suite, Microsoft Project and Microsoft Visio 2013.

• The network is centrally managed at the Head Office and all campuses are linked to the Head Office.

• Each campus is Wi-Fi enabled providing wireless connection to staff and students.

Q.4.1 Design an implementable routing and bridging solution for the network. Your

solution must address the following design and operation aspect of all routers.

Q.4.1.1 Functionality of the network layer.

Q.4.1.2 Design and implementation of data plane.

Q.4.2 Draw a detail diagram showing the design and implementation of Q.4.1 above.

A user’s laptop is shutting down unexpectedly. As a Network Technician, you discovered the “shutdowns” only happen when the laptop is moved from one room to another. You “reseat” the hard drive, memory, battery, and LCD cable, but the laptop continues to shut down. Explain what could be the cause of this issue, and how would you resolve it.