The meaning of port 0 in netstat output

Question

What is the meaning of port 0 in netstat -an output in Windows? I'm asking about socket in Foreign address column:

0.0.0.0:0

I know that 0.0.0.0 address means, that host is listening on all interfaces, but what is the function of port zero?

Answer 1

If you see this as the "Foreign" address, the meaning is slightly different – it's not about the interface; that would be the "Local" address.

All zeros in the "Foreign" column just mean that there is no remote address yet. The line represents a listening socket, which will accept connections from any address, any port. Those connections would be displayed as separate lines.

(From what I remember, in some early systems it used to be possible to create TCP sockets that would only accept connections from a specific host, a specific port, or both.)