What is DNS Filtering?

Domain Name System (DNS) functions as an Internet phone book. It works by converting your favorite URL – your favorite news site or blog – into a computer-friendly language. The language of IP addresses is made up of strings of digits such as Because remembering these digits for each of the websites you visit would be a headache, DNS converts them to the common names you are familiar with.

What is DNS Filtering?

DNS filtering is the practice of blocking rogue websites and filtering out dangerous or unsuitable information using the Domain Name System. This maintains the security of company data and gives businesses control over what their workers may access on company-managed networks. DNS filtering is frequently used in conjunction with a wider access control scheme.

DNS filtering is the process of restricting access to specified websites for a specific reason, most often content screening. If a website or a group of websites has caught a danger, then its IP address is banned by a DNS filter, and access to it is restricted. Adult, gambling, productivity drains, and sites considered to represent a major virus risk are all examples of sites that may be blacklisted.

How Does DNS Filtering Work?

DNS filtering is critical for organizations because it may drastically minimize the number of threats that a network is exposed to, reducing the remediation effort for MSPs and IT professionals. Effective DNS filtering may prevent up to 88 percent of Internet-borne malware from reaching the network.

  • When a user inputs a domain name into their browser, their device generates a DNS query and sends it to a DNS resolver, which is a specialized web server.

  • By requesting more DNS servers or validating its cache, the DNS resolver converts the requested domain name to an IP address.

  • The DNS resolver responds with the proper IP address to the user's device, which is referred to as "resolving" the domain.

  • To open a connection and begin loading the material, the user's device contacts the server at that IP address.

  • DNS is required for accessing online content; no material may be loaded until the DNS process has been completed. As a result, DNS filtering is a powerful tool for restricting what material consumers may access.

DNS filtering can be used to ban online sites based on their domain name or IP address, as follows −

  • By Domain Name − For some domains, the DNS resolver does not resolve or look up the IP addresses at all.

  • By IP Address − The DNS resolver tries to resolve all domains, but if the IP address is on the blocklist, it won't be returned to the asking device.

What is a Blocklist?

A blocklist is a list of known hazardous domains or IP addresses in the context of DNS filtering. DNS filtering companies can use blocklists shared by the cyber security community, create their own blocklists, or conduct a combination of the two. Some DNS filters will automatically assess URLs and add them to a blocklist. If malicious JavaScript code is found on example.com, for example, example.com will be added to the blocklist.

DNS filtering can also be used to block domains that are not necessarily utilized for malware or phishing attempts, but host prohibited or unsuitable material. For instance, a firm may want to include adultcontent- hosting websites to their DNS filtering blocklist. The reverse of a blocklist is an allowlist. An allowlist is a list of allowed domains or IP addresses. All domains or IP addresses that are not on the allowlist are blocked.

What Does It Mean to Have a Secure DNS Server?

As part of a DNS filtering service, a secure DNS server is a DNS resolver that filters hazardous or forbidden websites. Some secure DNS servers additionally provide enhanced privacy to protect user data; for example, Cloudflare's DNS resolving service purges all DNS query records after 24 hours.

There are other techniques to make the DNS process safer, in addition to DNS filtering, because DNS was not designed at first with security in mind. The DNSSEC protocol is used to ensure that DNS resolvers offer accurate information and has not been hacked. DNS over TLS (DoT) and DNS over HTTPS (DoH) encrypt DNS queries and answers, making it impossible for attackers to track a user's DNS inquiries.