An ISP redirect page is a spoof page served by major ISPs including: Cox Communications,[1] Embarq, Verizon, Rogers, Earthlink, and various others when World Wide Web users enter an invalid DNS name.
[citation needed] If a user types in an incorrect Uniform Resource Locator (URL), for example http://wikipedia.orf instead of http://wikipedia.org, the ISP's DNS server will respond with a spoofed DNS response that redirects the user to an advertising web page.
Every ISP runs a DNS server to allow their customers to translate domain names into IP addresses that computers understand and use.
When the ISP's DNS server receives a request for a name that is not recognized or is unavailable, some ISPs spoof the NX (null) response and instead return the IP address of a search or advertising page to the client.
When the client is using a web browser, this will display a search page that contains possible suggestions on the proper address and a small explanation of the error.