Port, domain name, protocol.

One . domain name

Each domain name corresponds to its IP Address , From left to right Top-level domain name , First level domain name , Two level domain name ....., The two are separated by dots . Search the web address through the domain name , In fact, the essence is also through IP Address search .

for example ：

You can search Baidu , Search directly www.baidu.com To search

You can also type ：

These two

www.baidu.com

14.215.177.39

The answer must be inevitable ,www.baidu.com Easier to remember

Two . port

Logical port , Generally speaking, it means TCP/IP Port in protocol , The port number range is from 0 To 65535, For example, for browsing Web Services 80 port , be used for FTP Service 21 Ports, etc .

3、 ... and . agreement

agreement : It is a series of sets that communicate between computers or devices in the network .

Common protocols are :

HTTP Protocol proxy server commonly used port number :80/8080/3128/9098

...... Wait for a series of agreements

Four .http://baidu.com:80

1.http          agreement

2.baidu.com    domain name

3.80                  port

5、 ... and .Tcp Three handshakes and four waves

(1） Three handshakes

A simple example

client :

Can you hear ？

The server ：

I can hear , And you? ？

client :

I can hear

(2) Four waves

client :

The client sends to the server FIN package , Need to disconnect .

The server :

Received your request to disconnect , Send a ACK, Do not send requests ,  But there is still data to be processed .

The server :

After the server has processed the data , Send a FIN, Indicates that the server can disconnect .

client ：

Received from the server FIN After the package , Send a ACK, Indicates that the client can also disconnect .

(3) Why does it take three handshakes , It takes four waves ?

Three handshakes ： Three handshakes are for TCP Connected .

Four waves : To disconnect , To ensure the end of data transmission , And receive data .