Nametoport

Nametoport refers to the process and mechanism by which a human-readable service name is translated into a numeric port number used by network protocols. This enables programs to refer to services such as http or smtp by name rather than by their associated port, typically for use with TCP or UDP.

The authoritative source for common name-to-port mappings is the IANA Service Name and Transport Protocol Port Number Registry. Local systems also maintain their own copies of mappings, most notably the /etc/services file on Unix-like systems, and analogous registries on other platforms. Port numbers allow the transport layer to demultiplex incoming traffic to the correct service, and they are defined per protocol (TCP or UDP) to prevent ambiguity.

Resolution of a name-to-port lookup is performed by standard library functions and system services. Examples include getservbyname in C, socket.getservbyname in various languages, and higher-level helpers such as net.LookupPort in some runtimes. The mapping is usually protocol-specific, so a service name can correspond to different ports for TCP and UDP. Common examples include http mapped to 80/tcp, https to 443/tcp, and ftp to 21/tcp.

Limitations include variability across systems and the existence of nonstandard or dynamic configurations. Some services may have multiple valid ports or use nonstandard ports in certain deployments. For dynamic service discovery, applications may rely on DNS SRV records or other discovery mechanisms rather than fixed name-to-port mappings.

See also: IANA service registry, /etc/services, getservbyname, DNS SRV, port number, service discovery.