Server machines use numbered ports to make their services available to the internet. Clients will then connect to a service on a specific web server port number and at a particular IP address. For instance, a server machine that is running on a web server would be available on port 80 while a file transfer protocol (FTP) server would be available on port 21.
Each recognizable service is available to the internet using a recognized port number. Some of the well-known port numbers include:
- Daytime 13
- echo 7
- time 37
- ftp 21
- telnet 23
- nameserver 53
- qotd (Quote of the Day) 17
- smtp (simple mail transfer; email) 25
- finger 79
- gopher 70
- WWW 80
- nicname 43 (who is)
A client can connect to a port from anywhere on the internet only if the server machine permits connections from outside the world and if the port is not protected by firewall. Also, when a client has connected to a service on a specified port number, it is able to access the service by use of a specific protocol. Protocols are texts that describe how the server and the client will have their conversation. All web servers on the internet comply with the hypertext transfer protocol.
Additionally, it is important to note that your sever machine could use any well-known port number. Port 80 is the port that the server receives from the web client, assuming that it was set or configured by default. However, servers are not necessarily confined to be available on port 80 alone.
When you load the web server software on your machine, you could put it on any unused port such as port 918.
This port will then be included in your URL in order to enable someone to reach your server. For example, if your machine is recognized as yyy.zzz.com, your URL needs to include your port number in order for others to connect to your server. Your URL will, therefore, be: http://yyy.zzz.com:918.
However, when the web server port number is not specified, the browser may assume that it is using port 80. This is because, by default, a web server’s port number is 80.