Network Fundamentals (Section 1)

I: Background of Internet Development

The number of computers has become less and more, and the solution of data transmission has evolved from a single computer to complete a certain function into a situation where multiple computers cooperate to complete a certain function

Local Area Network (LAN): no more than 10KM in distance
Metropolitan Area Network (MAN): Geographical range from tens of kilometers or even hundreds of kilometers
Wide Area Network (WAN): Geographical range from hundreds of thousandsMeters to thousands of kilometers, even tens of thousands of kilometers

Two: Network Protocol

Protocol: Agreed on the format of communication between the two parties to transmit information
Network protocol: Agreed on the format of the network host when transmitting data
Content completed by the network: Transfer data from the a process of the A host to the b process of the B host
Inter-process communication: The essence of the network is also the way of inter-process communication
Network data = protocol part + application layer data

Conclusion 1: The "data" in the network not only has the data itself but also the content of the protocol. The content of the protocol helps the data to be transmitted to be correctly transmitted to the other host in the network
Conclusion 2: The programs written based on the operating system library functions are all application layer programs, and the data generated is called application layer data
Conclusion 3: The protocol part is also used in the linux operating systemThe description method, the description itself is a structure, that is, the content of the protocol part is the structure data

Three: Network Protocol Layering

OSI protocol layering

Inotgo will express

TCP/IP Layered Mode

Purpose of protocol layering

Consider from the software level: decouple the functions of the network, some are responsible for application layer data, some are responsible for the transmission between terminals, some are responsible for routing, etc.
From the implementation level: layeringAmong them, each agreement can complete its own agreement part.

Four: Encapsulation and Separation of Network Data

Package

Share

Conclusion 1:When the application layer data is transmitted through the network, it needs to be encapsulated by the network protocol stack. After reaching the peer end, it needs to be divided by the network protocol stack.
Conclusion 2: When the network protocol stack is encapsulated, the content of the protocol is added.In order to transmit correctly in the network

Five: Getting to know the ip address and MAC address for the first time

ip address

Essence: The ip address of the ipv4 version is an unsigned 32-bit integer with a range of [0,2^32-1]
Function: Identify a host in the network
dotted decimal is another form of ip address. The four bytes are divided by one byte using "."
The range of each number is [0,2^8-1], which is [0,255]
Note: One ip address can only be occupied by one machine
One machine can occupy multiple ip addressesp>

MAC address

Essence: The length is 48 bits, 6 bytes, generally expressed in the form of hexadecimal numbers plus fire (such as 08:00:27:03:fb:19)
Function: identify a specific piecePhysical network card equipment, network card equipment will have a unique MAC address in the world when it leaves the factory.
(The transmission and reception of network data is ultimately related to the network card.)
The MAC address is used for the connection in the data link layer.Node