In computer networking, a port is a communication endpoint, a 16-bit number that identifies one service or process on a host. A port works with an IP (Internet Protocol) address and a transport protocol such as Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) to name a single connection endpoint. Port numbers run from 0 to 65535.
History of Port
Creator: No single creator. ARPANET developers, with Vint Cerf and Jon Postel (RFC 322). Year: 1972.
The concept of port numbers came from the early ARPANET developers. They worked through informal cooperation. Software authors and system administrators shared the work. The term port number did not exist at first. The early term was socket number. A socket number for a remote host was a 40-bit value. The last eight bits were called Another Eightbit Number (AEN).
On 26 March 1972 Vint Cerf and Jon Postel asked for a catalog. The catalog would list socket numbers for network services. RFC 322 asked administrators to report the function and socket numbers of their programs. The catalog was published as RFC 433 in December 1972. It listed each host, its port numbers and each function.
The catalog showed that some hosts used one number for different services. The authors promised a standard to resolve these conflicts. The Internet Assigned Numbers Authority (IANA) later became the registry. IANA keeps the official list of well-known and registered ports. It also coordinates other protocol resources, such as the DNS root and IP addresses.
Today a port belongs to a TCP or UDP socket. A process binds a socket to an IP address and a port number. The operating system sends each arriving packet to the matching socket. For TCP, only one process can bind to one address and port pair. A port conflict happens when two programs use the same port.
Changelog and latest update
RFC 6335 is dated August 2011. It sets the IANA procedures for the Service Name and Transport Protocol Port Number Registry. It explains how a service name is assigned. It also explains how a port is requested. Wikipedia says the rules for well-known ports are stricter than for registered ports.
The IANA registry records assignments for TCP and UDP. It covers well-known and registered ports. The registry page lists the expert reviewers for each protocol. It also shows the last update. Wikipedia notes one more point. The client side of a connection usually takes a high port. That port comes from the dynamic range.
The first registry function, in RFC 433, served mainly as documentation. It showed that some hosts used port numbers in conflict. The IANA registry now keeps the official list. The early catalogs began that list.
Latest update: IANA Service Name and Transport Protocol Port Number Registry, 2026-10-09
The IANA registry shows a last update on 9 October 2026. The page lists each service by name, port number and transport protocol. Requests for a port assignment follow the procedure in RFC 6335. The registry is the place to check an official port number.
Usage examples
A port number appears after the host name or the IP address, for example server.example.com:443. The operating system lists the ports that programs have opened, and the commands below show them. Some servers accept a port option, and a firewall rule can allow or block a port number. The five examples show a list of listening ports, a service lookup, a test web server, an Apache listen directive and a connection test.
ss -tlnpThe ss command shows socket statistics for the local machine. The t option selects TCP, the l option selects sockets in the listening state, the n option prints numbers instead of names, and the p option shows the program that owns each socket. The output lists the address and port that each service uses.
getent services httpsThe getent command reads the services database that the operating system keeps. The lookup for https prints 443/tcp, which is the default port of HTTPS. The same database lists the other standard services, such as ssh on port 22 and ftp on port 21.
python3 -m http.server 8000 \
--bind 127.0.0.1The Python module http.server starts a web server that shares the current folder. The number 8000 is the port. The bind option limits the server to the loopback address 127.0.0.1, so only this computer can reach it. A browser opens http://127.0.0.1:8000 to see the folder.
# httpd.conf
Listen 80
Listen 8080The Listen directive tells the Apache web server which port numbers to accept connections on. This example opens the standard HTTP port 80 and port 8080. Each Listen line adds one port, and the server answers requests that arrive on any of the listed ports.
nc -zv server.example.com 443The nc command with the z option sends no data and only checks whether a TCP connection can open. The v option prints the result. A reply that says succeeded means that a service accepts connections on port 443 of the host, and a failure means that the port is closed or blocked.
References
These sources are outside Websnoogie and were checked on 2026-10-12.
Port (computer networking)
Wikipedia
The encyclopedia article on network ports. It covers the port number range and the well-known, registered and dynamic ranges. It explains socket binding. It also covers the history from the ARPANET socket numbers in RFC 322 and RFC 433.
RFC 322: Well Known Socket Numbers
RFC Editor (IETF)
The ARPANET document from March 1972. Vint Cerf and Jon Postel asked each host administrator to report the socket numbers of its service programs. The replies led to the catalog published as RFC 433.
RFC 6335: IANA Procedures for the Management of the Service Name and Transport Protocol Port Number Registry
RFC Editor (IETF)
The IETF document from August 2011. It sets the procedures for the IANA port registry. It defines the service name rules and the port ranges. It describes how to request a port assignment.
Service Name and Transport Protocol Port Number Registry
IANA
The official IANA registry of service names and port numbers. It lists each assignment for TCP, UDP and other protocols. The page shows its last update, 9 October 2026. It also names the expert reviewers for each protocol.
RFC 793: Transmission Control Protocol
RFC Editor (IETF)
The IETF specification of the Transmission Control Protocol. It describes how TCP uses source and destination port numbers in each segment. It delivers data to the right process. It also defines the connection states of a socket.
Decide which network ports stay open
Every server has numbered ports, and each one works like a door. Web visitors use port 443 for secure pages and port 80 for plain ones. Other doors, such as mail or file access, serve other programs. Each open door is a path someone could test. Closing the ports you do not use lowers that risk. The decision belongs to the business owner, and it should rest on a clear reason.
We review the open ports on every server we manage. We close the ones no service needs, and we keep the ones your site and mail depend on. If your site is moving from another host, we confirm the ports on the new server before any switch. There is no charge to move a normal-size WordPress site. Larger sites carry a one-time fee of $199.
Not sure which doors your business needs? Phone 402-813-4034, daily from 7 am to 10 pm, and we will walk through the list with you. Or order a $300 website and we will set the ports to match its pages.
