Web Sharing on Your Mac with Mountain Lion
Web Sharing on your Mac running OS X Mountain Lion enables others to share documents on your computer through the web. You can set up a website just by adding Hypertext Markup Language (HTML) pages and images to the Sites folder in your Home folder, and then activating Web Sharing in the Sharing pane of System Preferences.
In a perfect world, that would be all it took. To get it to work, however, you may need to modify settings for your network, router, firewall, DNS server, and other web publishing-related minutiae.
Web Sharing works only while your Mac is connected to the Internet or an internal network, and it requires the speed of a direct connection. If you use a modem and connect to the Internet by dialing up, this capability won’t be a lot of use to you.
Furthermore, even if you keep your Mac connected to the Internet 24 hours a day with a Digital Subscriber Line (DSL) or cable-modem connection, using this feature could violate your agreement with your Internet service provider (ISP), because some ISPs prohibit you from hosting a website.
Also, most cable and DSL connections use dynamic IP address assignment through Dynamic Host Configuration Protocol (DHCP), which means your IP address will change from time to time.
On the other hand, some ISPs don’t care whether you run a website. Check with yours if you’re concerned.