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Some ports can be used for anything, while others have long-established purposes
By
Bradley Mitchell
Bradley Mitchell
Writer
- Massachusetts Institute of Technology
- University of Illinois
An MIT graduate who brings years of technical experience to articles on SEO, computers, and wireless networking.
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Updated on July 13, 2021
Reviewed by
Jon Fisher
:max_bytes(150000):strip_icc()/jonfishersquare-93eb80e77a004035887f56816d3623c5.jpg "Among Many Thousands of TCP and UDP Ports, Only a Few Are Very Popular (1)")
Reviewed byJon Fisher
- Wichita Technical Institute
Jonathan Fisher is a CompTIA certified technologist with more than 6 years' experience writing for publications like TechNorms and Help Desk Geek.
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The Transmission Control Protocol (TCP)uses a set of communication channels called portsto manage system messaging among several different applications running on the same physical device. Unlike the physical ports on computers like USB ports orEthernet ports,TCP ports are virtual—programmable entries numbered between 0 and 65535.
Most TCP ports are general-purpose channels that can be called into service as needed but otherwise sit idle. Some lower-numbered ports, however, are dedicated to specific applications. While many TCP ports belong to applications that no longer exist, certain ones are very popular.
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TCP Port 0
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TCP does not actually use port 0 for network communication, but this port is well-known to network programmers. TCP socket programs use port 0 by convention to request an available port be chosen and allocated by the operating system. This saves a programmer from having to pick ("hardcode") a port number that might not work well for the situation.
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TCP Ports 20 and 21
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FTP servers use TCP port 21to manage their side of FTP sessions. The server listens for FTP commands arriving at this port and responds accordingly. In active mode FTP, the server additionally uses port 20 to initiate data transfers back to the FTP client.
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TCP Port 22
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Secure Shell uses port 22. SSH servers listen on this port for incoming login requests from remote clients. Due to the nature of this usage, port 22 of any public server frequently gets probed by network hackers and has been the subject of much scrutiny in the network security community. Some security advocates recommend that administrators relocate their SSH installation to a different port to help avoid these attacks, while others argue this is only a marginally helpful workaround.
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TCP Port 23
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Port 23 governs telnet, a text-based system for logging into remote systems. Although modern remote-access approaches rely on Secure Shell on port 22, port 23 remains reserved for the older and less-secure telnet application.
TCP Ports 25, 110, and 143
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Email relies on several standard ports. Port 25 governs the Simple Mail Transfer Protocol — the tool by which an email on your computer makes its way to a mail server, and then from that server to the larger internet for routing and delivery.
On the receiving end, port 110 governs Post Office Protocol, version 3, and port 143 is dedicated to Internet Mail Access Protocol. POP3 and IMAP control the flow of emails from your provider's server to your inbox.
The secure versions of SMTP and IMAP vary depending on configuration, but ports 465 and 587 are common.
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UDP Ports 67 and 68
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Dynamic Host Configuration Protocolservers use UDP port 67 to listen for requests while DHCP clients communicate on UDP port 68.
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TCP Ports 80 and 443
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Arguably the single most famous port on the Internet, TCP port 80 is the default that HyperText Transfer ProtocolWeb servers listen on for Web browser requests.
Port 443 is the default for secure HTTP.
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UDP Port 88
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The Xbox network gaming service uses several different port numbers including UDP port 88.
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UDP Ports 161 and 162
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By default, the Simple Network Management Protocol uses UDP port 161 for sending and receiving requests on the network being managed. It uses UDP port 162 as the default for receiving SNMP traps from managed devices.
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TCP Port 194
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Although tools like smartphone messaging apps and services like Slack and Microsoft Teams have cut into the use of Internet Relay Chat, IRC still proves popular with people around the globe. By default, IRC uses port 194.
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Ports Above 1023
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TCP and UDP port numbers between 1024 and 49151 are called registered ports. The Internet Assigned Numbers Authority maintains a listing of services using these ports in order to minimize conflicting uses.
Unlike ports with lower numbers, developers of new TCP/UDP services can select a specific number to register with IANA rather than having a number assigned to them. Using registered ports also avoids the additional security restrictions that operating systems place on ports with lower numbers.
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