What port should be listening before a successful conne…

An administrator is configuring a secured webserver, however connecting to https://127.0.0.1 is not working. She runs netstat -ntl, which returns the following
output:
tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN
What port should be listening before a successful connection is possible? (Provide only the numerical value of the port)

Answer: See the explanation