Question

PART A 21 MARKS
SHORT ANSWER QUESTIONS Answer ALL questions from this part. Write your answers in the Examination Answer Booklet. Each question is worth 1.5 marks (14 x 1.5 = 21 marks).

Question 1
An organisation has been granted a block of addresses with the mask /22. If the organisation creates 8 equal-sized subnets, how many addresses (including the special addresses) are available in each subnet? Show your calculations.

Question 2
Give an example of a valid classful address that has a mask of 255.255.0.0

Question 3
Briefly explain the function of “path MTU discovery” in IPv6 routing.

Question 4
What is the size of an IPv4 header with 12 bytes of options?

Question 5
TCP/IP uses various types of addresses. What type of address is the address 210.77.124.12:51200 ?

Question 6
Briefly explain what is an ephemeral port number, and its function in TCP/IP communications.

Question 7
In your own words, briefly explain the function of the expiration timer in RIP.
Question 8
What is the primary function of DNS servers?

Question 9
In wireless networking, what is an Extended Service Set (ESS)?

Term 2 Standard Examination 2017

COIT20261 — Network Routing and Switching


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Question 10
Explain when do routers forward packets out through the default route?

Question 11
Briefly explain why routers consult ARP during the forwarding process.

Question 12
What is the purpose of the TTL field in the base header of an IPv4 datagram?

Question 13
List three differences between UDP and TCP.

Question 14
In an IPv6 datagram, what are extension headers and where are they located?























Term 2 Standard Examination 2017

COIT20261 — Network Routing and Switching


Page 4 of 6
PART B 15 MARKS
PRACTICAL PROBLEMS Answer ALL questions from this part. Write your answers in the Examination Answer Booklet. Show your calculations.


Formula from Forouzan
To calculate the number of addresses N in a block: N = 232-n To calculate a subnet mask given the prefix n: n + Log2 (N/Ni) To calculate first addresses: AND the mask with the given address To calculate last addresses: OR the complement of the mask with the given address

Question 1 4 Marks
Consider the following block of classless addresses: 145.87.117.3/29
Identify the addresses in this range that would be used as the network address, those that can be used by network hosts, and the direct broadcast address.


Question 2 4 Marks
A company has been granted a block of addresses which starts at 200.100.20.0/25. Create the following 6 subnets for this company by calculating the subnet address for each subnet. (a) 2 subnets with 32 addresses each (b) 4 subnets with 16 addresses each


Question 3 2 Marks
A router receives a packet. List three of the logical processes the router would perform in processing that packet.

  

Term 2 Standard Examination 2017

COIT20261 — Network Routing and Switching


Page 5 of 6

Question 4 5 Marks
The figure below shows the configuration of a hypothetical section of the Internet.

200.11.60.0/24 140.21.0.0/22 m1 200.11.60.1/24 m2 140.21.0.1/22 R 2 mo 150.3.0.2/16 Rest of the Interhet R4 m1 mo m0 150.32.0.0/18 150.3.0.0/16 150.3.0.116 150.32.0.1/13- 150.3.0.4/16 mo 150.3.0.3/16 m2 161 22.0.1/18 m1 220.10.40.1/24 R3 220.10.40.0/24 161.22.0.0/18

Construct the routing table of router R3 for this configuration by copying and completing the following table in the Examination Answer Booklet.

Answer: Mask Network address Next-hop address Interface

  PART C 24 MARKS LONG ANSWER QUESTIONS Answer the following questions with as much detail as you can. Write your answers in the Examination Answer Booklet. Use your own words.


Question 1 6 Marks
Organisation-A is a large enterprise that has one class-A network address for all its needs.   

Discuss the addressing problem that Organisation-A could face with its one class-A network and how it could use subnetting to help it to overcome that problem. (3 marks) How would the situation be different if Organisation-A had gotten a classless (CIDR) address instead? (3 marks)


Question 2 6 Marks
Name one distance vector routing protocol and one link state routing protocol. Compare the two protocols in terms of the cost metrics they use.

Question 3 6 Marks
The period between the phasing out of IPv4 and the general adoption of IPv6 is referred to as the “transition period”. Describe the main methods being developed or proposed to allow IPv4 and IPv6 to run concurrently during this period.


Question 4 6 Marks
In wireless network architecture, the Basic Service Set (BSS) has two possible formats. Identify these two formats and briefly explain the difference between them.

Answer 1

We are allowed to do only 4 exercise out of any given.

Answer 1
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Network       Subnet mask   Size       Range               Broadcast ip
********
192.168.1.0   255.255.255.224   30   192.168.1.1 to 192.168.1.30       192.168.1.31
192.168.1.32   255.255.255.224   30   192.168.1.33 to 192.168.1.62       192.168.1.63
192.168.1.64   255.255.255.224   30   192.168.1.65 to 192.168.1.94       192.168.1.95
192.168.1.96   255.255.255.224   30   192.168.1.97 to 192.168.1.126       192.168.1.127
192.168.1.128   255.255.255.224   30   192.168.1.129 to 192.168.1.158   192.168.1.159
192.168.1.160   255.255.255.224   30   192.168.1.161 to 192.168.1.190   192.168.1.191
192.168.1.192   255.255.255.224   30   192.168.1.193 to 192.168.1.222   192.168.1.223
192.168.1.224   255.255.255.224   30   192.168.1.225 to 192.168.1.254   192.168.1.255

Answer 2
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Network       Subnet mask   Size       Range               Broadcast ip

10.0.0.0   255.0.0.0   16777214   10.0.0.1 to 10.255.255.254   10.255.255.255
or
10.0.0.0/24

Answer 3
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When a host receives a datagram too big message, it MUST reduce its estimate of the PMTU for the relevant path, based on the value of the next-Hop MTU field in the message. A host MUST never reduce its estimate of the Path MTU below 68 octets.

Answer 4
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The Internet Protocol (IP) is defined in RFC 791. The RFC specifies the format of the IP header. In the header there is the IHL (Internet Header Length) field which is 4 bits long and specifies the header length in 32 bit words. The IHL field can hold values from 0 (Binary 0000) to 15 (Binary 1111).

So the longest Internet Header (IP header) size can be 15*32 Bits = 480 Bits = 60 Bytes. This is why the header has a maximum size of 60 Bytes.

The shortest header size is 20 bytes, where the IHL field has the value 5 (0101). This is because all the required fields in the header need 20 Bytes of space. So while in theory you could set the IHL to a value < 5 this would always be an incorrect value and thus an invalid packet header.

Answer 5
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its ipv4 address with port number after : colon is port number and before colon is ip address from class C network.

Answer 6
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An ephemeral port is a short-lived endpoint that is created by the operating system when a program requests any available user port. The operating system selects the port number from a predefined range, typically between 1024 and 65535, and releases the port after the related TCP connection terminates.

Answer 7
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Expiration Timer: The Expiration clock determines to what extent a steering section can be in the directing table without being refreshed. This is additionally called as termination Timer. As a matter of course, the worth is 180 seconds. After the clock terminates the jump check of the directing section will be set to 16, denoting the goal as inaccessible.

Answer 8
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The principle capacity of DNS is to make an interpretation of area names into IP Addresses, which PCs can get it. It additionally gives a rundown of mail servers which acknowledge Emails for every area name. Every space name in DNS will assign a lot of name servers to be definitive for its DNS records.

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