Þjónustuport

Þjónustuport, in English “service port,” refers to a numeric identifier that helps direct network traffic to a specific service running on a host. In IP networks, communication is addressed by an IP address and a port number; the port portion indicates the service the client intends to reach on the host. Ports are 16-bit numbers, allowing values from 0 to 65535. The well-known ports, from 0 to 1023, are traditionally assigned to widely used services; registered ports from 1024 to 49151 are assigned by IANA to specific applications; dynamic and private ports from 49152 to 65535 are typically used temporarily by clients.

IANA maintains the official Port Registry, which pairs port numbers with the protocol (TCP or UDP) and service names. Examples widely used include HTTP on port 80, HTTPS on port 443, SSH on port 22, and SMTP on port 25. For DNS, UDP port 53 is common, while DNS over TCP uses the same port. Applications may listen on multiple ports, and a single port can host different services on different IP addresses or protocols.

In practice, service ports are central to firewall rules, network address translation, and load balancing. Administrators may restrict access to certain ports, forward external ports to internal hosts, or route traffic across network segments. Security considerations emphasize proper authentication and encryption rather than relying solely on obscurity of non-standard ports. Understanding the role of þjónustuport helps in configuring connectivity, securing services, and planning network architectures.