If you write "www.wikipedia.com:80" in a browser's address bar, Wikipedia's home page will load just as if you had simply written "www.wikipedia.com". However, if you write "www.wikipedia.com:20", you will get an error. Why is that? The first option loads the page because it calls for the correct IP address for web surfing (i.e., 80); the second option does not work because it calls for the IP address for file transfer rather than for web surfing (i.e., 20). The first option loads the page because it calls for the logical address of Wikipedia's website (i.e., 80); the second option does not work because it calls for the physical address of Wikipedia's website (i.e., 20). The first option loads the page because it calls for the correct IP address for web surfing (i.e., 80); the second option does not work because it calls for the IP address for email communication rather than for web surfing (i.e., 20). The first option loads the page because it calls for the correct port number for web surfing (port 80); the second option does not work because it calls for the port number for file transfer rather than for web surfing (port 20). The first option loads the page because it calls for the correct MAC address for web surfing (i.e., 80); the second option does not work because it calls for the MAC address for file transfer rather than for web surfing (i.e., 20).