Port 81 is a network port number that can be used by applications and services. Ports, in the context of computer networks, are communication endpoints for processes running on devices. They are designated by numbers, and each unique number corresponds to a specific process or service.
Port 81 is not assigned by the Internet Assigned Numbers Authority (IANA) for a specific well-known service like, for example, HTTP on port 80 or HTTPS on port 443. However, it’s commonly used as an alternative port.
Some common uses of port 81 include:
- Alternative Web Server Port: Because port 80 is the standard port for HTTP, port 81 is sometimes used as an alternative for HTTP traffic, especially in situations where port 80 is already being used by another service on the server.
- Web-based applications: Some web-based applications or tools might default to using port 81 to avoid conflicts with other services.
- Proxies and Caching: Some proxy or caching servers might use port 81.
- Custom Services: Any custom service can use port 81 if it’s free and if the developer decides to use this port.
However, when using non-standard ports like 81 for web services, users might need to explicitly specify the port in the URL, e.g., http://example.com:81.
As always, if you’re running a service on a non-standard port, it’s essential to ensure that it’s secure and monitored, especially if it’s exposed to the internet. It’s also a good practice to check the documentation or settings of any software or service you’re running to understand which ports are in use and for what purpose.