Chapter 1 Overview-Reading Notes and 1-Reading Notes

Chapter 1 Overview-Reading Notes and 1-Reading Notes
Chapter 1 Overview of TCP/IP protocol-Reading Notes
Author: vpoetDate:Note: The articles in this series are only the author's understanding of the TCP/IP protocol, which may inevitably result in leakage or incompleteness. Of course, they may also be superficial. I hope you can understand them.

I. IntroductionBaidu encyclopedia says the TCP/IP protocol:The abbreviation of Transmission Control Protocol/Internet Protocol is the Transmission Control Protocol/Internet Interconnection Protocol, also known as network communication Protocol. It is the most basic Internet Protocol and the basis of the Internet, it consists of the IP protocol of the network layer and the TCP protocol of the transport layer. TCP/IP defines how electronic devices connect to the Internet and how data is transmitted between them. The protocol uses a layer-4 hierarchy. Each layer calls the protocol provided by the next layer to fulfill its own needs. In layman's terms: TCP is responsible for discovering transmission problems. When there is a problem, it sends a signal and requires a re-transmission until all data is securely and correctly transmitted to the destination. The IP address specifies an address for each Internet device on the Internet.
Now let me talk about my understanding:The open System Interconnection open model is a standard model provided by a certain organization for network Interconnection. Remember, it is just a model. It is like this. To express originality, I try to draw images as much as possible.

Well, based on the entire theoretical model, a certain organization in the United States has defined and implemented the TCP/IP protocol. This protocol is the Protocol we use for network connection, remember that TCP/IP is a protocol family, which means it has many protocols,Well, since the TCP/IP protocol is defined and implemented in the OSI model, the relationship between the two is probably as follows:

The TCP/IP protocol integrates the first three layers of OSI into one layer, while the transport layer and the network layer remain unchanged. The physical layer is the combination of the data link layer and the physical layer in the OSI model.








Ii. Significance of TCP/IP layers and significance of each layer
First, the application layer is based on various protocols implemented by the underlying protocol, which can be accessed by our users, such as the Telnet protocol used for remote logon, for example, SMTP (Simple Mail Transfer Protocol) for sending emails, pop3 protocol for receiving emails, etc.Secondly: the transport layer, the book says that the transport layer provides end-to-end transmission, which is so obscure that I don't understand what the terminal is. My understanding is that the transport layer uses ports to implement the communication between two hosts, because the IP address encapsulation at the network layer already provides the Host IP address information, the transport layer only needs to provide the port information of an IP address to recommend communication with the corresponding port of the host. The Transport Layer Protocol includes TCP and UDP. TCP is reliable. What is reliable? It means that TCP communication guarantees the communication process, what is guaranteed? ensure that information is sent from the source machine to the target machine. The mechanisms used include connection establishment and timeout retransmission. What does UDP mean by being unreliable or unreliable? I just want to send it to you. If you cannot receive it, it will be irrelevant to me.Third, the main protocol at the network layer is the IP protocol, and the network layer is the network interconnection. What does it mean to provide connections between hosts, and this connection is based on IP addresses, theoretically, as long as each host connected to the Internet has a unique IP address, we can use this unique IP address to connect to any computer, but it is ideal, the reality is very skinny. IPv4 is not enough, which means that each computer cannot be divided into unique IP addresses, but science and technology are the first productivity. You know there is always a solution, such as dividing subnets, DHCP is used to relieve the pressure on the IP address, but this is not fundamental. It is simply because the implementation and development of IPv6 can fundamentally solve this problem, provide enough IP addresses to every terminal connected to the Internet in the world.The best thing is that the physical layer is also called the network interface layer. The main purpose of this layer is to provide physical details of network transmission. This layer includes many protocols, such as the most popular Ethernet protocol.



Iii. IP addresses and portsIP address is very important. Why is it important? Without this, we cannot connect to the entire Internet. The number of IP addresses provided by IPv4 is theoretically insufficient, so some organizations are actively promoting IPv6 standards.IPv4 includes 32 bits, which are usually expressed as, for example, 192.168.1.1.But in the memory, it is still in binary format, similar to 10000000011000000000000100000001.
Its structure is similar to this:

This is the structure of five types of IP addresses,We can convert the network number into a dot-based 10-digit system:Class A: 0.0.0.0-127.255.255.255Class B: 128.0.0.0-191.255.255.255Class C: 192.0.0.0-223.255.255.255Class D: 234.0.0.0-239.00000000255Class E: 240.0.0.0-247.255.255.255
Increases in number of sites from the A-E network and decreases in number of hostsWhat does this mean: allocate A Class A address, which can contain 2 ^ 24 hosts, and assign A class C address with only 2 ^ 8 (256) hosts
We can also determine whether such an IP address is a type of IP address Based on a number in decimal order. Of course, if there is a subnet division, you cannot determine the type of address to determine the number of hosts,It must be determined by combining the subnet mask.
I want to explain about subnet division in the following blog.

Of course, there are some special IP addresses, which will be reserved for future blog posts.





Iv. DNS ServiceThe DNS Domain Name System is a service provided by the Internet. When accessing the internet, you need to enter the website you want to browse in the browser. Generally, you need to enter the Domain Name of the website,Why use a domain name? It is easy to remember because it is easy to use a domain name. I can't imagine how painful it would be to visit the server through IP addresses. How is this DNS implemented? In fact, DNS resolution is implemented throughEach DNS server maintains a default domain name and IP address ing table. When we access a website through a domain name, the domain name first enters the DNS server, and thenIn the domain name IP ing table, if the corresponding IP address is queried, and then the server is accessed through IP address addressing, if the ing item is not found, then it will continue searching in the DNS server at the upper level.
We can run the ipconfig/all command in dos to query the IP address of the local DNS server.


V. TCP/IP communication process
So here, we would like to ask how the TCP/IP protocol family can implement communication connections between hosts.Here I only have to continue to use my painting skills and Imagination:

The word is too ugly.
This is the TCP/IP communication process, but it is actually the process of packet unpacking and encapsulation. What we need to learn next is what packet unpacking methods are available at each layer, the differences between the packet unpacking methods form different protocols in each layer.
Well, here we are. If there are any errors, I hope you can correct them more.