Common TCP and UDP ports

What are common TCP ports?

FTP: defines the file transfer protocol. Port 21 is used. It is often said that a certain host has enabled the FTP service, which is the file transfer service. You must use the FTP service to download files and upload them to the home page.

TELNET: Are you on BBS? In the past, BBS was a character-only interface. The server supporting BBS opened port 23 to provide external services. In fact, Telnet really means remote login: You can remotely connect to the host as your identity.

SMTP: defines the Simple Mail Transfer Protocol. Currently, many email servers use this Protocol to send emails. The server opens port 25.

HTTP: This is the most widely used protocol-Hypertext Transfer protocol. You need to use it to browse Web pages online, so the host that provides web resources must open port 80 to provide services. We often say that "WWW Service" and "web server" mean this.

POP3: corresponds to SMTP. POP3 is used to receive emails. Generally, POP3 uses port 110. In free email boxes such as 263, almost all of them have the POP3 receiving function. That is to say, as long as you have the POP3 protocolProgram(For example, Foxmail or outlook), you do not need to log on to the mailbox interface in Web mode, that is, you can receive emails.

What are common UDP ports?

DNS: domain name resolution service. Each computer on the Internet has a network address corresponding to it. This address is what we often call an IP address, which is expressed in pure numbers. However, this is inconvenient to remember, so a domain name appears. When accessing the host, you only need to know the domain name. The domain name and IP address change is completed by the DNS server. The DNS uses port 53.

SNMP: Simple Network Management Protocol. port 161 is used to manage network devices. Because of the large number of network devices, the unconnected services show their advantages.

Chat Software OICQ: The program of OICQ provides both services and services, so that the two chat talents are equal. OICQ uses a connectionless protocol. Its server uses port 8000 to listen for information. The client uses port 4000 to send information externally. If the above two ports are in use (many chat with a few friends at the same time), add them in sequence.

Note later:TCP (Transport Control Protocol) is a reliable connection-oriented communication protocol. To ensure the reliability of transmission, technologies and measures such as validation and re-transmission will be taken; user Data Protocol (UDP) is a non-reliable connection protocol. Although the reliability is not guaranteed, but it also has advantages such as high transmission efficiency and simple protocol. Both protocols belong to the transport layer. Based on the network layer (such as the IP layer), they play their respective advantages in different application fields, such as oicp, the UDP protocol is used because of the high transmission efficiency and speed, but the low requirement on reliability. (Tip:If you use Skynet firewall and monitor UDP packets, you can view the IP address of the Peer when sending and receiving information in oicp)