The Most Popular TCP and UDP Port Numbers

The Transmission Control Protocol (TCP) uses a set of communication channels called ports to manage among multiple different applications running on the same physical device. Unlike the physical ports on computers like USB ports or Ethernet 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.

1
TCP port 0

Transmission Control Protocol (TCP) Header
Transmission Control Protocol (TCP) Header.

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.

2
TCP ports 20 and 21

FTP servers uses TCP port 21 to 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.

3
TCP port 22

Secure Shell (SSH) 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.

4
UDP ports 67 and 68

Dynamic Host Configuration Protocol (DHCP) servers use UDP port 67 to listen for requests while DHCP clients communicate on UDP port 68.

5
TCP port 80

Arguably the single most famous port on the Internet, TCP port 80 is the default that HyperText Transfer Protocol (HTTP) Web servers listen on for Web browser requests. 

6
UDP port 88

The Xbox Live Internet gaming service uses several different port numbers including UDP port 88.

7
UDP ports 161 and 162

By default the Simple Network Management Protocol (SNMP) 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.

8
Ports above 1023

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.