If you are browsing online, you will likely encounter a wide range of threats, some of which could lead to your bank account being emptied or sensitive information being exposed and your accounts being compromised. Then there is ransomware, which could be used to prevent you from accessing your files should you not have backups. DNS filtering offers an easy way to protect against these threats.

The majority of websites now being created are malicious websites, so how can you stay safe online? One solution deployed by businesses and ISPs is the use of a web filter, with DNS filters one of the best choices for filtering the Internet. A DNS-based web filter can be set up to restrict access to certain categories of Internet content and block most malicious websites.

While it is possible for companies or ISPs to purchase appliances that are located between end users and the Internet, DNS filters allow the Internet to be filtered without having to buy any hardware or install any software. So how is DNS filtering operated?

How Does DNS Filtering Work?

DNS filtering – or Domain Name System filtering to give it its full name – is a technique of preventing access to certain websites, webpages, or IP addresses. DNS is what permits easy to remember domain names to be used – such as Wikipedia.com – rather than typing in IP addresses – such as DNS maps IP addresses to domain names.

When a domain is bought from a domain register and that domain is hosted, it is given a unique IP address that allows the site to be found. When you try to access a website, a DNS query will be carried out. Your DNS server will look up the IP address of the domain/webpage, which will permit a connection to be made between the browser and the server where the website is hosted. The webpage will then be opened.

So how does DNS filtering operate? With DNS filtering set up, rather than the DNS server returning the IP address if the website exists, the request will be subjected to certain security measures. If a particular webpage or IP address is recognized as malicious, the request to access the site will be denied. Instead of connecting to a website, the user will be sent to a local IP address that will display a block page explaining that the site cannot be opened.

This control could be implemented at the router level, via your ISP, or a third party – a web filtering service provider. In the case of the latter, the user – a business for example – would point their DNS to the service provider. That service provider keeps a blacklist of malicious webpages/IP addresses. If a site is known to be malicious, access to malicious sites will be prevented.

Since the service provider will also group webpages, the DNS filter can also be implemented to block access to certain categories of webpages – pornography, child pornography, file sharing websites, gambling, and gaming sites for example. Provided a business sets up an acceptable usage policy (AUP) and sets that policy with the service provider, the AUP will be live. Since DNS filtering is low-latency, there will be next to no delay in logging onto safe websites that do not breach an organization’s acceptable Internet usage policies.

Can a DNS Filter Prevent Access to All Malicious Websites?

Sadly, no DNS filtering solution will stop access to all malicious websites, as in order for this to be accomplished, a webpage must first be identified as malicious. If a cybercriminal creates a brand-new phishing webpage, there will be a delay between the page being set up and it being reviewed and added to a blocklist. However, a DNS web filter will prevent access to the majority of malicious websites.

Can DNS Filtering be Avoided?

Proxy servers and anonymizer sites could be deployed to mask traffic and bypass the DNS filter unless the chosen solution also prevents access to these anonymizer sites. An end user could also manually amend their DNS settings locally unless they have been locked down. Determined persons may be able to find a way to bypass DNS filtering, but for the majority of end users, a DNS filter will block any effort to access forbidden or harmful website material.

No single cybersecurity solution will let you to block 100% of malicious websites but DNS filtering should definitely form part of your cybersecurity operations as it will allow most malicious sites and malware to be blocked.