Overview of TCP/IP Study Notes

Overview of TCP/IP learning Notes 1. hierarchical network protocols are generally developed at different levels, and each layer is responsible for different communication functions. A protocol family, such as t c p/I P, is a combination of multiple protocols at different levels. T c p/I P is generally considered as a layer-4 protocol system. The following figure shows the four layers of the TCP/IP protocol family www.2cto.com. Each layer is responsible for different functions. 1) link Layer: sometimes referred to as the data link layer or network interface layer. It usually includes the device driver in the operating system and the network interface card corresponding to the computer. They work together with the physical interface details of the cable (or any other transmission medium. 2) network layer: it is also called the Internet layer to process group activities in the network, such as group routing. In the t c p/I p protocol family, network layer protocols include I P protocol (Internet Protocol ), I c m p protocol (I n t e rn e t Internet Control Packet protocol), And I g m p protocol (I n t e r n e t Group Management Protocol ). 3) Transport Layer: Provides end-to-end communication for applications on two hosts. In the t c p/I P protocol family, there are two different transmission protocols: T C P (Transmission Control Protocol) and U D P (User Datagram Protocol ). T c p provides high-reliability data communication for the two hosts. The work it does includes dividing the data that an application has handed over to it into small pieces and handing it over to the network layer below, confirming the received group, and setting the timeout clock for sending the final confirmation group. Because the transport layer provides high-reliability end-to-end communication, the application layer can ignore all these details. On the other hand, u d p provides a very simple service for the application layer. It only sends a group called a datagram from one host to another, but it does not guarantee that the datagram can reach the other end. Any required reliability must be provided by the application layer. Note: These two transport layer protocols have different purposes in different applications. 4) Application Layer: responsible for handling specific application details. Almost all different t c p/I P implementations provide the following common applications: www.2cto.com • Telnet, FTP and e-mail • FTP file transfer protocol. • SMTP Simple Mail Transfer Protocol. • SNMP Simple Network Management Protocol. •... 2. TCP/IP layer in the t c p/I P protocol family, there are many protocols. (Figure 2) protocol www.2cto.com of different levels in the TCP/IP protocol family 3. Data encapsulation when the application transmits data with t c p, the data is sent to the protocol stack, each layer is then sent to the network as a string of bit streams. Each layer adds some header information (sometimes tail information) to the received data, as shown in process 3. The data unit that t c p sends to I P is called the T C P packet segment or the T C P packet segment (T C P s e g e n t ). The data units that I p sends to the network interface layer are called I P datagram (IP datagrams ). A bit stream transmitted over Ethernet is called a frame (Fr a m e ). The physical feature of an Ethernet data frame is that its length must be 4 to 6 ~ Between 1 and 5 0 bytes. A group can be either an I p datagram or a piece of an I P datagram (f r a g m e n t ).
(Figure 3) The encapsulation process u d p when data enters the protocol stack is basically consistent with t c p data. The only difference is that the unit of information that u d p sends to I P is called U D P datagram (UDP datagrams), and the header length of U D P is 8 bytes. Www.2cto.com because t c p, u d p, I c m p and I g m p both need to transmit data to I P, therefore, I p must add an identifier to the header of the generated I P to indicate the layer of data. Therefore, I p Stores an 8 B I t value in the header, which is called the Protocol domain. 1 stands for the I c m p Protocol, 2 stands for the I G M P protocol, 6 stands for the T C P protocol, and 1 7 stands for the U D P protocol. Similarly, many applications can use t c p or u d p to transmit data. The Transport Layer Protocol stores an Application Identifier when generating the message header. T c p and u d p use a port number of 1 6 B I t to represent different applications. T c p and u d p respectively store the source port number and destination port number into the packet header. The Network Interfaces must send and receive the I P, A R P, and R A R P Data respectively. Therefore, you must add an Application ID to the Ethernet frame header, to specify the network layer protocol for data generation. Therefore, the Ethernet frame header also has a 16-bit frame type domain. 4. Ethernet data frame sharing when the target host receives an Ethernet data frame, the data starts to rise from the bottom of the protocol stack and removes the packet header added to each layer of protocols. Each layer of the Protocol box should check the protocol ID in the packet header to determine the upper layer protocol for receiving data. This process is called sub-use (D e m u l t I p l e x I n g). Figure 4 shows how this process occurs. (Figure 4) the Ethernet data frame sharing process www.2cto.com for the Protocol I c m p and I G M P positioning has always been a tricky thing. In (Figure 2), place them on the same layer as I p because they are actually affiliated to I P. But here, we put them on the I P layer because ICMP and IGMP packets are encapsulated in IP datagram. For a r p and r a r p, place them above the drivers of the Ethernet device because they both have their own Ethernet data frame types, just like the I P datagram. But sometimes a r p is placed under the I P layer as part of the Ethernet device driver. The reason is logical. For unpacking t c p, the destination port number, source I P address, and source port number are used to unpack the package.