Tcp udp connection problems (1)

In some network security measures, we will focus on protecting some special network protocols. For example, we will talk about tcp udp. The use of these two protocols is incomparable in network security. In some firewall software, we can see the settings for these two protocols. Figure 1 shows the interface for setting rules for the firewall software of Rising's Personal Edition. Careful readers will find that the "protocol" column in Figure 1 contains "TCP", "UDP" and other terms. What do they mean? Now let's talk about tcp udp.

Connection-oriented TCP

"Connection orientation" means that a connection must be established with the other party before formal communication. For example, if you call someone else, you must wait until the line is connected and the other party picks up the microphone to talk to each other.

Figure 1

TCPTransmission Control Protocol (Transport Control Protocol) is a connection-based Protocol. That is to say, you must establish a reliable connection with the other party before sending and receiving data. A TCP connection can be established only after three "conversations". The process is very complicated. Here we only provide a simple and visual introduction. You only need to understand this process. Let's take A look at the simple process of the three conversations: host A sends A connection request packet to host B: "Can I send data to you ?", This is the first conversation. Host B sends A packet to host A that agrees to the connection and requires synchronous synchronization, that is, the two hosts are sending, receiving, and coordinating): "Yes, when will you send it? ", This is the second conversation. host a sends another packet to confirm that host B's request is synchronized: "I will send it now, let's proceed !", This is the third dialogue. The purpose of the three "dialogs" is to synchronize the transmission and receipt of data packets. After the three "dialogs", host A formally sends data to host B.

The TCP protocol can provide reliable communication connections for applications, so that the byte stream sent by a computer is sent to other computers on the network without error. for data communication systems with high reliability requirements, the TCP protocol is often used to transmit data.

Figure 2

To better differentiate tcp udp protocol, we will conduct an experiment to install Windows 2000 Server operating system on computer) copy A 8,644,608-byte file from computer B on "Network Neighbor". The following figure shows the sending and receiving indicators through the NIC in the lower right corner of the status bar: although data streams flow from computer B to computer A, computer A still sends 3,456 packets, as shown in figure 2. How are these packets generated? Because the TCP/IP protocol is used for file transmission, or connection-oriented TCP protocol is used, when computer A receives data packets, it needs to send back data packets to computer B, therefore, some traffic is generated.

Figure 3