1 Network Architecture
The more mainstream network architectures are the ISO/OSI reference model and the TCP/IP protocol suite. Both architectures adopt a layered design and implementation approach. The ISO/OSI reference model is divided into application layer, presentation layer, session layer, transport layer, network layer, data link layer and physical layer from top to bottom. TCP/IP divides the network into application layer, transport layer, network layer and link layer. The advantage of layered design is that each layer can be designed and implemented independently. As long as the calling specification and interface between adjacent layers remain unchanged, the internal implementation of each layer can be easily and flexibly changed for optimization or other requirements.
2 Network Protocols
A network protocol is a collection of rules, standards or conventions established for data exchange in a computer network. Syntax, semantics and timing are the three elements of a network protocol. Simply put, semantics means what to do, syntax means how to do it, and timing specifies the order in which each time appears. The syntax and semantics are relatively easy to understand, and some readers may wonder why the time and order of various times should be strictly specified. Imagine that two colleagues, A and B, meet at the door of the company at work at 8:00 in the morning. A asks B, "Have you eaten?", B leaves without answering (how to calculate the psychological shadow area of A), and leaves work at 12 noon When the two met again at the door of the company, B said "eat" to A, and we can imagine what A's eyes would look like when he looked at B.
(1) Grammar: The grammar specifies the structure and format of user data and control information.
(2) Semantics: Semantics is used to explain the meaning of each part of the control information, specifying what kind of control information needs to be sent, and what actions need to be completed and what kind of responses should be made.
(3) Timing: Timing is a detailed description of the sequence of events, and can also be called "synchronization".
3 Application Layer Protocols
Application layer protocols interact directly with end users to determine how messages are passed between applications running on different end systems. The following is a brief list of common application-layer protocols in the collection.
(1) DNS: Domain Name System (Domain Name System), used to realize the conversion of domain names and IP addresses, runs on UDP, and uses port 53 by default.
(2) FTP: File Transfer Protocol, which can transfer files between different platforms through the network. It is a clear text transfer protocol based on TCP and works on port 21 by default.
(3) HTTP: HyperText Transfer Protocol, which runs on top of TCP and uses port 80 by default.
(4) SMTP: Simple Mail Transfer Protocol (Simple Mail Transfer Protocol), based on TCP, uses clear text to transmit mail and send commands, and uses port 25 by default.
(5) TELNET: Remote login protocol, running on top of TCP, using port 23 by default.
4 Transport Layer Protocols
Two protocols, Transmission Control Protocol (TCP) and User Datagram Protocol (UDP), are mainly run at the transport layer. TCP is a connection-oriented, reliable transmission protocol with quality assurance, but the overhead is relatively high. Large; UDP is a connectionless protocol that transmits as much as possible, with low overhead, and is often used in applications such as video on-demand. There is no difference between TCP and UDP in themselves, but only in different places of application. In the transport layer, the port number is used to identify and distinguish multiple application layer processes running on the same computer. Whenever an application layer network process is created, the system will automatically assign a port number to associate it, which is to achieve end-to-end on the network. An important foundation for communication. For example, remote desktop connection occupies port 3389 by default, HTTP uses port 80 by default, MySQL uses port 3306, MongoDB uses port 27017, in most cases IRC server uses port 6667, IMAP uses port 143, Oracle uses 1521, 1158, 8080, 210, etc. Several ports, etc.
5 IP address
IP runs at the network layer and is an important foundation for network interconnection. IP addresses (32-bit or 128-bit binary numbers) are used to identify hosts on the network. On an open network or within the same local area network, each host must use a different IP address; and due to network address translation (Network Address Translation, Wide application of technologies such as NAT) and proxy servers, hosts between different intranets can use the same IP address. The IP address and the port number together identify a specific application process on a specific host on the network, commonly known as Socket.
6 MAC address
The MAC address, also known as the physical address of the network card, is a 48-bit binary number used to identify the physical address of different network cards. The IP address and MAC address of the machine can be viewed using the ipconfig-all command in the command prompt window.