A brief introduction of TCP/IP four-layer model and OSI seven-layer model

Table 1-1 is the TCP/IP four-layer model and the OSI seven-layer model table. We correspond the OSI seven-layer network model with the Linux TCP/IP four-layer conceptual model, and then categorize the various network protocols.

Table 1-1 TCP/IP four-layer model and OSI seven-layer model corresponding table

OSI Seven layer network model	Linux TCP/IP four-layer conceptual model	Corresponding network protocol
Application Layer (application)	Application Layer	TFTP, FTP, NFS, WAIS
Presentation Layer (presentation)	Telnet, Rlogin, SNMP, Gopher
Conversation Layer (session)	SMTP, DNS
Transport Layer (transport)	Transport Layer	TCP, UDP
Network Layer (Network)	Internet Layer	IP, ICMP, ARP, RARP, AKP, UUCP
Data Link Layer	Network interface	FDDI, Ethernet, Arpanet, PDN, SLIP, PPP
Physical Layer (physical)	IEEE 802.1A, IEEE 802.2 to IEEE 802.11

1. Network interface

The network interface puts the data link layer and the physical layer together and corresponds to the network interface of the TCP/IP conceptual model. The corresponding network protocols are mainly: Ethernet, FDDI, and any protocols that can transmit IP packets.

2. Internet Layer

Network layer corresponding to the Linux TCP/IP conceptual model of the Internet Layer, Network layer protocol management of discrete computer data transmission, such as IP protocol for users and remote computers to provide information packet transmission method, to ensure that packets can correctly reach the target machine. In this process, the IP and other network layer protocols are used for data transmission, and if there are no tools for monitoring system processes, users cannot see the IP in the system. The network sniffer sniffers is a device that can see these processes (it can be software or hardware), it can read every packet sent over the network, read any activity that occurs at the network layer protocol, so the network sniffer sniffers poses a security threat. Important network layer protocols include ARP (Address Resolution Protocol), ICMP (Internet Control Message Protocol) and IP Protocol (Internetwork Protocol) and so on.

3. Transport Layer

The transport layer corresponds to the transport layer of the Linux TCP/IP conceptual model. The transport layer provides communication between applications. Its functions include: Format the flow of information, and provide reliable transmission. To achieve the latter, the Transport Layer Protocol stipulates that the receiving end must send back confirmation information, and if the packet is lost, it must be sent again. The transport layer includes TCP (Transmission control Protocol, Transmission Control Protocol) and UDP (user Datagram Protocol, Subscriber Datagram Protocol), which is the most important protocol in the transport layer. TCP is based on IP, defines the data transmission format and rules of program to program on the network, provides the transmission confirmation of IP packets, the request of lost packets, and the mechanism to reassemble the packets received according to their sending order. A TCP protocol is a connection-oriented protocol, similar to a phone call, in which you must establish a clear connection before you can begin transmitting data. UDP is also based on IP, but it is a connectionless protocol, and transport between two computers is similar to delivering messages: messages are sent from one computer to another without a clear connection. UDP does not guarantee the transmission of data, nor does it provide a reordering or a re-request function, so it is unreliable. Although the reliability of UDP restricts its application, it has better transmission efficiency than TCP.