CSC00240 Data Communication and Networks: 1335092

Question 1          [15 Points]

  1. Given the subnet mask of 255.255.240.0 and the broadcast address 140.20Y.1X1.255, find the network address. Here X is the first digit of your student ID and Y is the last digit of your student ID.    (2 Points)

Mask: 255.255.240.0

BroadCast: 140.200.121.255

Network Address: 140.202.112.0/28

  • Given the Host Address 50.70.178.22X and the Broadcast Address 50.70.191.255, find the Network Address. How many usable host addresses are available in this subnet? Here X is your student IDs fourth digit. (3 Points)

Host Address 50.70.178.225

Network Address: 50.70.128.0

Usable host addresses: 50.70.128.1 – 50.70.191.254

  • You have been given the Network Address 180.12.3X.0/23.  If you have to make provision for at least 110 hosts per subnet, write the Subnet Mask and addresses of the first and last useable subnets. What is the Broadcast Address of these two subnets? Here X is the remainder left when you divide the second digit of your student ID by 5. For example, if the second digit of your ID is 2, then remainder of 2/5 is 2.  (3 Points)

Network Address 180.12.33.0/23

Subnet Mask: 255.255.255.128

first and last useable subnets

Broadcast Address

 First Usable addressLast usable addressBroadcast Address
180.12.33.0 /25180.12.33.1180.12.33.126180.12.33.127
180.12.255.0 /25180.12.255.1180.12.255.254180.12.255.255
  • Consider the network diagram below in Figure 1:

Figure 1

A network engineer subnets the above network diagram according to the table below:

NetworkNetwork AddressMask using /
Chatswood LAN192.168.0.0/7
Sydney LAN192.168.0.128/8
Melbourne LAN192.168.1.128/8
Geelong LAN192.168.2.128/5
Geelong North LAN192.168.2.160/5

The network engineer uses the address as its starting point: 192.168.0.0/23. Has the network engineer made errors/mistakes/inefficient design decisions? If so, how would you correct them? (7 Points)

The corrected table will be

NetworkNetwork AddressSlash
Sydney LAN200.200.100.0/24
Melbourne LAN200.200.101.0/24
Chatswood200.200.102.0/25
Geelong LAN200.200.102.128/26
Geelong North LAN200.200.102.192/27

Question 2          [15 Points]

1. We have learned in class that TCP is a reliable protocol. Considering this, answer the questions below:

(a) Can an application running over UDP send data reliably? (2.5 Points) 

Yes. The reliability can be added at application layer.

(b) Why would an application developer, who wants to build an application which sends data reliably, want to use UDP instead of TCP?     (2.5 Points)

UDP is considered by the developer because UDP requires less networking resources and it is geared towards fast delivery.

2. The header fields for TCP (Figure 2) and UDP (Figure 3) are shown below (recall 1 byte = 8 bits):

Figure 2

Figure 3

The Data field in both figures signifies the data from the application layer while the other fields are the TCP (the number in brackets are the bit length of the particular field) and UDP header fields, respectively. Assuming that the transport layer always breaks the data (from the application layer) into 1000 bytes chunks (for both protocols) for application A before adding the Transport layer header, what is the overhead (extra number of bytes sent) if TCP was used instead of UDP to transmit 1 million segments of application A. You can assume all segments reached the destination without errors. You can also assume that the options field in the TCP header is 32 bits for all the segments. (5 Points)

3. A source and a destination start a TCP connection. They agree on a window size of 5000 bytes and a maximum segment size of 1000 bytes. The total data (sent by the application layer) to be transported is 5 GBytes. After the three-way handshake takes place, the source starts transmitting data to the destination. The sequence number of the first segment for data transmission is 1. The source sends 3 segments and then receives an acknowledgement for the 3 segments. The source then sends four more segments but receives acknowledgement of only two. What is the number (out of 5GBytes) of the last byte of the window after the sequence of events described above? (5 Points)

Question 3        [15 Points]


                            

Table 1                                                                                      Table 2


Table 3

Three routing tables of the three routers in a network are shown in the tables above. Routes with R represent routes learned from a dynamic routing protocol. Answer the following questions.

  1. A packet arrives at the interface of R1 with IP address 192.168.2.1. What is the network address of the network from which this packet originates? (2 Points)

192.168.2.0/24

  • A packet with source IP 192.168.3.10 and destination IP 10.0.0.4 at R3. What does R3 do with the packet? (2 Points)

The packet will be dropped because there is no route towards 10.0.0.4 network

  •  Which routers will route the packet through it’s journey to the destination if the source IP is 192.168.1.4 and destination IP is 192.168.2.6? (5 Points)

Router 3 and Router 2

  • Identify (give network addresses) the LANs and WANs in the network? (3 Points)
LAN/WANNetwork Address
LAN 1192.168.1.0/24
LAN 2192.168.2.0/24
LAN 3192.168.3.0/24
WAN 1172.16.0.0/30
WAN 2172.16.0.4/30
  • What network connects the following devices (if no network exists, say no network):
    • R1 and R2 (1.5 Points)
    • R1 and R3 (1.5 Points)

R1 and R2  è 172.16.0.0/30

R1 and R3 No network

Question 4        [15 Points]

Figure 2

For the questions below assume that each layer 3 device has communicated with each other previously.

1. Which of the following devices build a MAC table (answer in table below):        (1.5 Points)

PC B

2. Using your answers from above, please explain how the device(s) above use/uses the table they/it possess/possesses?                            (4 Points)

When the switch receives a packet on the network, it checks the MAC address of the destination and source if they exist in the MAC table, if they do, it will forward the packet to the destined node, if not the switch will flood its MAC table with this MAC address except where it originated from.

3. Fill-out the following MAC Address table and the device name (answer in table below):   (4.5 points)

Device Name:  _Sw1_______ (Pick any appropriate device from the above topology)

MAC Address Table (Use as many entries as you think appropriate)

VLAN1AA:00:00:00:AA:11
VLAN1AA:00:00:00:AA:22
VLAN1AA:00:00:00:AA:44
VLAN1AA:00:00:00:AA:33
  
  

4. What role does R1 play when PC A pings PC B? (2.5 Points)

R1 does not play any role because PC A and PC B are in the same LAN, therefore they can ping one another without intervention of a router

5. If PC A pings IP address 8.8.8.8, what will be the destination MAC address in the encapsulated frame?                             (2.5 Points)

The destination MAC address will be the MAC address of interface of the next router

Question 5        [15 Points]

You are accessing a webpage, http://example.com, on your browser. You type in exactly: http://example.com (This is made up and has no relationship to any example.com if it exists at the time of your examination). You check the status of your web request using the network option in your browser. In your request you see the following:


Remote Address: 13.55.4.72:X (Recall from lecture that this is a socket.)
Status: 302 Moved Permanently


Please answer the following questions:

  1. What does 13.55.4.72 represent and what role is it playing here? (1.5 Points)
    13.55.4.72 is the IP of destination machine.
  • How did your browser come to know about 13.55.4.72? (1.5 Points)
    the DNS service enables the interpretation of IP address to domain name.
  • What do you expect X to be? (2 Points)

X is expected to be the port number

The 302 Moved Permanently status is telling you that the webpage you are looking for has moved permanently. Your browser automatically generates a new request for the webpage. The webpage is now open on your browser. You check the URL of the webpage on your browser which is: https://www.example.com. You inspect the request for this webpage and you see the following:

Remote Address: 13.55.8.93:Y

Status: (Not shown here as you will have to answer a question about it)

Answer the following questions:

  • What do you expect Y to be? (1 Points)
    Y also is the port number
  • What do you expect to see as the status? (3 Points

The expected status will be 400 because the page opened on local machine

  • What is www is referring to in the URL above? Here we are not asking what the acronym WWW stands for. (3 Points)
    this is the information system in which documents and rest of web are identified by the URL linked by the hypertext
  • Why do you think the webpage was moved? (3 Points)

The page was moved and 302 is used to redirect users to anew site for a given short time during the update or redesign of the webpage