In the old days, we used
telnet to see if a port on a remote host was open:
telnet hostname port would attempt to connect to any port on any host and give you access to the raw TCP stream.
These days, the systems I work on do not have telnet installed (for security reasons), and all outbound connections to all hosts are blocked by default. Over time, it's easy to lose track of which ports are open to which hosts.
Is there another way to test if a port on a remote system is open – using a Linux system with a limited number of packages installed, and
telnet is not available?