ARP protocol with MAC address learning, TCP protocol, way of identifying addresses

1 c/S

client<------>server based on network communication
browser<------>server based on network communication

The server side must meet the criteria:
1, stable operation (network, hardware, operating system, server application software), has been providing services to the outside

2, the server must be bound to a fixed address

2 What is the Internet
Two major elements
1, the underlying physical connection media, is to pave the way for communication
2, a unified communication standard---"Internet Communication protocol

Internet Protocol is the English language in the computer world

3 Custom Protocols
Any communication protocol must contain two parts:
1. Header: must be fixed length
2. Data


0000 0000.0000 0000.0000) 0000.0000 0000
1111 1111.1111 1111.1111) 1111.1111 1111


172.16.10.1/24

172.16.10.1
255.255.255.0000 0000



172.16.10.1:10101100.00010000.00001010.00000001
255.255.255.255.0:11111111.11111111.11111111.00000000
Subnet Address: 10101100.00010000.00001010.00000000
172.16.10.0



172.16.10.2:10101100.00010000.00001010.00000001
255255.255.255.0:11111111.11111111.11111111.00000000
Subnet Address: 10101100.00010000.00001010.00000000
172.16.10.0

4 How addresses are identified

    Ip+mac will be able to identify a computer that is unique across the world
    Ip+mac+port can identify a unique network communication-based application software worldwide.
    URL address: Identify a resource that is unique across the world


DNS default Port  53

5 TCP Protocol (reliable Protocol)
    Three-time handshake to establish a connection
    Four waves to disconnect the connection

    1, why connect to three times and disconnect but need four times

Three-time handshake is to establish a connection, when the connection is established and no data four waves to lose the connection because the client and the server has generated data interaction, the           client sends the request only disconnects the client and the server connection, and the server may have           other data is not delivered, All must be four times    

    2, why the TCP protocol is a reliable protocol, and UDP protocol is unreliable protocol

TCP calls the operating system, the operating system sends data, accept the other side of the confirmation message will be emptied data advantages: Data security      shortcomings: Low productivity UDP is sent directly, after the deletion of the advantages: high efficiency        disadvantage: Data insecurity

    3, the TCP protocol establishes the connection and the disconnection state information as well as the meaning of the expression

Syn_sent: Send Request listen: Receive Message status SYN_RCVD: Received request established: Connection established

Fin = 1: Represents a disconnect request SYN = 1: Represents a connection request ACK = 1: Represents a confirmation request

Fin_wait_1: Active Disconnect Request close_wait: Receive message, wait for shutdown status fin_wait_2: Passive disconnect last_ack: Wait for the last connection time_wait: If the server has a large number of time_wait , then it means the service is being attacked.

6 Half-Connection pool
    Limit the number of requests at the same time, not the number of connections

ARP protocol with MAC address learning, TCP protocol, way of identifying addresses