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This article mainly explains "what are the basic knowledge points of computer network". The content of the explanation in the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought. Let's study and learn what are the basic knowledge points of computer network.

Ⅰ. Division of network hierarchy

In order to establish a computer network on a larger scale, the International Organization for Standardization (ISO) put forward the "Open system Internet reference Model" in 1978, namely the famous OSI (Open System Interconnection) model.

In addition to the standard OSI layer 7 model, the common network layer division is the TCP/IP layer 4 protocol, and the corresponding relationship between them is shown in the following figure:

Ⅱ. OSI seven-layer network model

Whether it is the seven-layer model of OSI or the four-layer model of TCP/IP, each layer must have its own exclusive protocol to complete its own work and communicate between the upper and lower layers. Let's take a closer look at the seven-tier model of OSI:

⑴ physical layer

The physical layer is the most basic network structure, which is composed of a variety of devices. This layer provides a reliable physical media for the upper layer protocol to transmit data. To put it simply, the physical layer ensures that the original data is transmitted on various physical media.

⑵ data Link layer

The data link layer provides services to the network layer on the basis of the physical layer, and its most basic service is to reliably transmit the data from the network to the target network layer of the adjacent nodes.

The functions of this layer include: physical address addressing, data framing, flow control, data error detection and retransmission, etc.

Main protocol: Ethernet protocol

Important equipment: bridge, switch

⑶ network layer

The purpose of the network layer is to realize the data transmission between the two end systems.

Many protocols are designed in the network layer, including the core protocol of the most important protocol TCP/IP-IP protocol. IP protocol only provides unreliable and connectionless transport services. IP protocol is matched with address resolution protocol ARP, inverse address resolution protocol RARP, Internet message protocol ICMP and Internet group management protocol IGMP.

Important equipment: router

⑷ transport layer

The first end-to-end, host-to-host level; the transport layer is responsible for segmenting the upper layer data and providing end-to-end, reliable or unreliable transmission. In addition, the transport layer also has to deal with end-to-end error control and flow control

Mainly include protocols: TCP protocol, UDP protocol

Important equipment: gateway

⑸ session layer

The session layer manages the session processes between hosts, that is, it is responsible for establishing, managing, and terminating sessions between processes. The session layer also uses the insertion of checkpoints in the data to achieve data synchronization.

⑹ presentation layer

The presentation layer transforms the upper data or information to ensure that the application layer information of one host can be understood by the application of another host. The data conversion in the presentation layer includes data encryption, compression, format conversion and so on.

⑺ application layer

Provides an interface for operating systems or network applications to access network services.

Ⅲ. IP address

The IP address consists of two parts: network bits + host bits.

Network part: used to describe the network scope of the specified host

Host part: used to describe the specific location of a specified host in a specific network scope

⑴ IP address classification: (this means that the IPv4 address defined by the IPv4 protocol consists of 32-bit binaries.)

Class A: the first binary bit is 0, the network bit is 8 bits; 0.0.0.01127.255.255.255

Class B: the first two binary bits are 10, the network bits are 16 bits, 128.0.0.0 bits 191.255.255.255

Class C: the first three binary bits are 110, the network bits are 24; 192.0.0.0 223.255.255.255

Category D: 224-239

Class E: 240-255

Class D and Class E do not divide network bits and host bits.

⑵ category A, B, C private addresses

In order to solve the problem of IP address exhaustion, increase the number of times to take IP address; it can be reused, but the Internet cannot route it.

Class A: 10.0.0.0amp 8, with a range of 10.0.0.0charges 10.255.255.255

Category B: 172.16.0.0amp 12, the range is: 172.16.0.0inch 172.31.255.255

Class C: 192.168.0.0amp 16, with a range of 192.168.0.0cm 192.168.255.255

⑶ reserved addresses (loopback addresses) cannot be selected for IP addresses used by other host configurations,

0.0.0.050.255.255.255

127.0.0.05127.255.255.255

⑷ automatically assigns address fields:

169.254.0.05169.254.255.255

⑸ network address: address with host bits all zeros (binary bits all zeros)

For example: 1.0.0.0 represents the name of a range

⑹ broadcast address: an address with all host bits of 1

For example: 1.255.255.255: represents all IP addresses in the entire network segment as the destination address

⑺ directed broadcast address:

255.255.255.255: represents all IP addresses in the entire IP address stack as the destination address

Ⅳ. Division of subnet mask

With the continuous expansion of Internet applications, the disadvantages of IPv4 are gradually exposed, that is, the network bits occupy too much, and the host bits are too few, so the host addresses it can provide are becoming more and more scarce. at present, in addition to the self-allocation of reserved addresses within the enterprise using NAT, a high-class IP address is usually re-divided to form multiple subnets for different sizes of users.

In fact, subnetting is to increase the number of network bits in IP addresses and reduce the number of host bits, so as to narrow the range of broadcast domains, reduce the number of hosts in logical network segments, and facilitate the accurate application of management and security policies.

Ⅴ. TCP / IP protocol

TCP/IP protocol is the most basic protocol of Internet, which is composed of IP protocol of network layer and TCP protocol of transport layer.

TCP is a connection-oriented communication protocol, which establishes a connection through a three-way handshake and removes the connection when the communication is completed. Because TCP is connection-oriented, it can only be used for end-to-end communication. TCP provides a reliable data flow service. TCP uses a method called "sliding window" for flow control, which actually represents the receiving capacity and is used to limit the sending speed of the sender.

The header format of the TCP message:

16-bit source port

16-bit destination port number

32-bit serial number: range (1-2 ^ 32-2) SEQ

The sequence number of the first segment is randomly selected

The sequence number of the second segment: the sequence number of the previous segment + the data part size of the previous segment + 1

...

32-bit confirmation number: range (2 ~ 2 ^ 32-1)

The receiver acknowledges the data that has been received and requires the sender to continue to transmit the identification of subsequent data segments.

Generally speaking, the confirmation number is the sequence number of the next segment to be sent by the sender

4-bit header length, 24-60 bytes

3-bit reserved flag bit

3-bit authenticated encryption flag bit

6-bit TCP feature flag bit:

Urg: emergency pointer flag bit; if the flag position 1, the forwarding priority of the data will be raised so that such data is forwarded first; if the URG flag bit of multiple data is set to 1 at the same time, the larger the emergency pointer of the next 16 bits, the higher the priority

ACK: the confirmation flag bit related to connection management; used to respond to the party initiating the connection establishment request or dismantling request

PSH: advance bit, if the flag position 1, the receiver can not add the data to the cache queue, directly to the application process for processing

RST: resets the connection flag bit; reconstructs the TCP connection flag bit when the TCP connection runs out or fails

SYN: synchronization flag bit, which is used to signal that the party who initiates the connection establishment request initiates the connection during the process of establishing a TCP connection

FIN: end connection flag bit. If the flag position is 1, the other party will instruct that the TCP connection will be dismantled. Just confirm it.

16-bit window size: mainly to achieve traffic negotiation and control, can prevent network congestion

Slide the window:

Congestion window:

Emergency window:

The size of the window means the number of segments we can transmit at a time.

16-bit segment checksum: checksum information that ensures the integrity of the data

16-bit emergency pointer: used to prioritize URG flag bits when they are all set to 1

Option: timestamp of segment segmentation

Connection-oriented features of the TCP protocol:

1. Connection establishment; three-way handshake

1) the sender generates a TCP header data, in which the source and destination ports are given by the application layer protocol; the serial number is randomly selected, the confirmation number is 0, and the flag bit SYN is set to 1.

2) after receiving the SYN request data sent by the sender, the receiver judges whether it can complete the data communication required by the other party; if so, it returns a TCP header data generated by it; the source and destination ports are opposite to the previous data; the sequence number is random, the confirmation number is the sequence number of the next data of the other party, and the two flag bits of SYN and ACK are set 1 at the same time.

3) after receiving the response data from the other party, the sender checks whether the ACK flag bit is set to 1; if it is 1, check whether the SYN flag bit is set to 1, and if it is also 1, confirm it; then generate the second TCP header data; the sequence number is the sequence number of the previous data + 1, and the confirmation number is the sequence number of the receiver's next data; ACK flag position 1

two。 Remove the connection and wave four times

1) when all data transmission is finished, one party actively sends a FIN header data of TCP flag position 1 to the other party.

2) after receiving the data of such FIN setting 1, the other party responds to the confirmation data of an ACK setting 1

3) the other party initiatively sends out a FIN set 1 data, requesting to remove the connection

4) the active Terminator confirms and sends the TCP header data of ACK setting 1

Ⅵ .UDP protocol

UDP user data protocol is a connectionless communication protocol. UDP data includes destination port number and source port number information. Because communication does not need connection, broadcast transmission can be realized. UDP communication does not require confirmation by the receiver, so it is an unreliable transmission and packet loss may occur.

UDP and TCP are on the same floor

UDP header:

16-bit source port: the port number chosen by the sender when encapsulating data. Generally speaking, the source port number of the data sent by the client is a randomly selected free port.

16-bit destination port: the port number that the receiver of this data communication must use when transferring data from the transport layer to the application layer; generally speaking, the destination port number of the data is fixed.

16-bit UDP length: the length of the entire Datagram, including the header

16-bit UDP checksum: the checksum of the entire UDP Datagram ensures data integrity to a certain extent.

Thank you for your reading. the above is the content of "what are the basic knowledge points of computer network". After the study of this article, I believe you have a deeper understanding of what are the basic knowledge points of computer network. the specific use of the situation also needs to be verified by practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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