When a client is looking to access a resource either via a web browser or from a command-line tool, they most often rely upon some sort of name resolution service to map the name of the host, domain, or resource to an IP address rather than specifying it directly. It is impractical to type in http://216.58.216.196 every time you want to access https://google.com, since it is much easier to remember the name rather than the IP address. Furthermore, it is unlikely that an individual will know what IP addresses each hostname maps to since DNS and NBNS have been set up to eliminate this requirement. An attacker can use this to their advantage by manipulating the results that these name resolution services provide to users and then redirecting their requests to resources that he controls and trick them into divulging sensitive information or to sites that can exploit various host or browser vulnerabilities.