SERVERPORT

A server port, commonly referred to simply as a port, is a logical endpoint used by a server to identify a specific process or service for network communication. When combined with an IP address, a port forms a socket address that transport protocols such as TCP and UDP use to deliver data between hosts. The port number indicates which application on the host should receive the data.

Port numbers range from 0 to 65535. Port 0 is reserved. Ports 1 through 1023 are well-known ports reserved for standard services and are typically assigned by IANA. Ports 1024 through 49151 are registered ports allocated for specific services, while ports 49152 through 65535 are dynamic or private ports used temporarily by clients for outbound connections or by servers for nonstandard services.

Servers commonly listen on well-known ports corresponding to their services, such as HTTP on TCP port 80, HTTPS on TCP port 443, and SSH on TCP port 22. Some services may operate on nonstandard ports or multiple ports. UDP ports are used by services that do not require a persistent connection, for example DNS typically uses UDP port 53, with TCP used for larger responses.

Access to server ports is governed by network configuration, including firewalls and NAT/port forwarding. Opening a port on a firewall increases exposure to potential attacks, so administrators restrict access to trusted clients. Privileged ports (those below 1024) usually require elevated privileges to bind on many operating systems. Clients typically use ephemeral source ports, while servers maintain long-running listening ports.

Common administration tasks include listing listening ports, diagnosing binding conflicts, and verifying firewall and NAT rules. Tools such as netstat, ss, or lsof help identify active ports and their associated processes. See also IANA port registry, TCP, UDP, firewall, NAT, port forwarding, and port scanning.