DNS blocking

<a href="/facts/Domain_Name_System/rfxdWFsj">Domain Name System</a> blocking, or DNS blocking / filtering, is a strategy for making it difficult for users to locate specific <a href="/facts/Internet_domain/FDLD2m5G">domains</a> or websites on the <a href="/facts/Internet/Xw1rVvJU">Internet</a>. It was first introduced in 1997 as a means to block <a href="/facts/Spam_email/ARJr6Aem">spam email</a> from known malicious <a href="/facts/IP_address/z9V22Sw9">IP addresses</a>.
DNS blocking can also be applied for outgoing <a href="/facts/HTTP/TWtvf7JD">requests</a> as well. Instead of returning the valid <a href="/facts/IP_address/z9V22Sw9">IP address</a> of a requested site (for example, instead of 198.35.26.96 being returned by the DNS when "www.wikipedia.org" is entered into a browser, if this IP were on a block list, the DNS might reply that the domain is unknown or with a different IP address that directs to a site with a page stating that the requested domain is not permitted). The latter case where the user is redirected to another destination would be considered <a href="/facts/DNS_Spoofing/k85Akwm4">DNS Spoofing</a>, otherwise known as "DNS Poisoning". DNS blocking can be applied to individual servers/IP address, or entire blocks of IP addresses for multiple reasons.
Some public DNS Resolvers, like <a href="/facts/Quad9/YbaFDb5s">Quad9</a> and CleanBrowsing, offer filters as part of their DNS. Quad9, for example, blocks access to known phishing and malicious domains. CleanBrowsing filters out adult content in their effort to protect kids online.

DNS blocking open-in-new

DNS blocking