I) TCI/IP Model :

First of all, let's talk a little bit about TCP/IP model .
When we talk to each other, we use the same language so everyone can understand .
If computer A wants to send file to computer B, both of them need to use the same language called "Protocol" .

TCP /IP is the most popular stack of Protocols our computers use nowaday to communicate .
TCP/ IP actually is a set of many protocols (for example when computer wants to send e-mail, it uses a protocol named SMTP, when it sends file - it uses FTP ....),  its name is represented by 2 protocols : TCP & IP . So hence the name TCP/IP .

II) IP Address :
 1) Introduction to IP Address :

- Every computer has to have at least 1 IP address to communicate with others . Just like my house has a address so some girls can send me some gifts .
- When we talk about IP address, we often talk about IP v4 (v = Version) : It comprises 32 bits (1 & 0) , and divides to 4 portions (called Octet ) separated by 3 dots (.) :
For example : 10000000.11000000.10000001.00000001 
- It's kind of hard to remember so people write it in decimal number : 128.192.129.1
(* You need to know how to convert from Binary to Decimal Number - just search on Google)

- IP addresses also have 2 parts : Host ID and Net ID , just like your house's address has Street number and House number .


2) IP address class :

- Classes help us to determine how many bits  net id (or host id) owned , notice : bits net id + bits host id = 32 (please take a look at the figure above) .

- Five classes : 
  • Class A : Net ID owns 8 bits, Host ID owns 24 bits .
  • Class B : ------------- 16 -------------------16 .
  • Class C : ------------- 24 -------------------8 .
  • Class D & E : are used for research & multicast .
- So how to know which class this IP address  1.2.3.4 belongs to ? 
- Focus on first octet, for example IP address is X.Y.Z.T 
if
  • X from 1     -> 126 : This IP belongs to class A
  • X from 128 -> 191 : This IP belongs to class B
  • X from 192 -> 223 : This IP belongs to class C
  • X from 224 -> 239 : This IP belongs to class D
  • X from 240 -> 255 : This IP belongs to class E
 X = 127 is used for other purposes . For example : 127.0.0.1 is called loopback address .

3) Public & Private IP address :

a) Public IP address : 
- In WAN (Internet)
- Is provided by Service Provider
- Unique in Internet

b) Private IP address : 
- In LAN (Local Area Network)
- Is provided by Administrator .



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