COMP2300 - lab09 - CECS

Week 12

Students are expected to attempt ALL of the questions in the Multi choice, Short answer and Lab quesitons. They will be discussed and marked at the beginning of the lab.

Multi choice

Question: Which of the below are NOT advantages of memory paging and segmentation?

A) It saves memory
B) It adds security
C) It increases memory size
D) It adds reliability

Question: What is the hexadecimal number associated with the IP address 192.168.1.95?

A) 0xC0A8015F
B) 0x5F01A8C0
C) 0xF5108A0C
D) 0x0C8A10F5

Question: What is the IP address associated with the hexadecimal number 0x0A013D36?

A) 160.16.211.99
B) 10.1.61.54
C) 162.212.16.100
D) 192.168.1.45

Short answer

Question: What are three advantages or disadvantages of using the UDP network protocol?
Question: What are three advantages or disadvantages of using the TCP network protocol?

Lab questions

Excercise:

IP Addresses

An IP address is an unsigned 32-bit integer. Because internet hosts can have different host byte ordering (remember talking about big and little endian machines!) TCP/IP defines a uniform network byte ordering. Unix provides functions htonl(), htons(), ntohl(), ntohs() to convert between network and host byte order.

Use man pages to determine what each of the above functions do.
partch is a machine on the student network. Using one of the above functions to write a short (~10 line) C program to determine which byte ordering this machine uses.
Is network byte ordering big or little endian?

IP addresses are typically presented to humans in a form known as dotted-decimal notation, where each byte is represented by its decimal value and separated from the other bytes by a period. Internet programs convert back and forth between IP addresses and dotted decimal strings using the functions inet_pton() and inet_ntop() (where n denotes network representation, while p denotes application representation).

Complete the following table (assuming network byte ordering):

Hex Address	Dotted-decimal address
0x0	_______________
0xffffffff	_______________
0xef000001	_______________
_______________	205.188.160.121
_______________	64.12.149.13
_______________	150.203.24.4

Write a program hex2dd.c that converts its hex command line argument to a dotted-decimal string and prints out the result. Hint: use the "%x" format specifier in sscanf(), consulting the man pages for this function and inet_ntop(). You can compile it with gcc -o hex2dd hex2dd.c -lnsl.
```
    $ ./hex2dd 0x8002c2f2
    128.2.194.242
    
```
Write a program dd2hex.c that converts its dotted-decimal argument to hex and prints out the result
```
    $ ./dd2hex 128.2.194.242
    0x8002c2f2
    
```
Note that if you recompile and run these programs on a system with different endians, you get different hex numbers generated. However, combining the conversions should give the same result on either host:
```
    $ ./hex2dd `./dd2hex 128.2.194.242`
    128.2.194.242
    
```

In-class Group Task

Get into groups of 4 people. Two of the group members should write a server program on one computer and the other two should write a client on another computer. The aim is to get across a secret message of at least 20 characters from the server end to the client end without speaking to each other, apart from vital information such as the IP address and port number for the server.
When you have achieved this, there will be a class discussion about the methods people used.
If there is still time left, modify your programs so that you can send files from the server to the client. This will be simpler if you first send an integer representing how large the file is, then receive that many bytes.