IP blocking prevents the connection between a computer or network and certain IP addresses or ranges of addresses. IP blocking effectively bans undesired connections from those computers to a website, mail server, or other Internet server.
IP banning is commonly used on computer servers to protect against brute force attacks. Both companies and schools offering remote user access, and people wanting to access their home computers from remote locations, use Linux programs such as BlockHosts, DenyHosts or Fail2ban for protection from unauthorized access while allowing permitted remote access.
It is also used for censorship. One example is the July 2003 decision by techfocus.org to ban the Recording Industry Association of America (RIAA) and Motion Picture Association of America (MPAA) from its website for various abuses by those two organisations of the content on it.
On an Internet forum or Web site an IP ban is often used as a last resort to prevent a disruptive member from access, though a warning and/or account ban may be used first. Dynamic allocation of IP addresses can complicate incoming IP blocking, rendering it difficult to block a specific user without blocking a larger number of IP addresses, thereby risking collateral damage caused by ISPs sharing IP addresses of multiple internet users.

IP Blocking of the Showtime website for non-US origins
IP banning is also used to limit the syndication of content to a specific region. To achieve this IP-addresses are mapped to the countries they have been assigned to.
Proxy servers can be used to bypass an IP ban unless the site being accessed has an effective anti-proxy script.