Venture online and you will be faced with a wide range of threats, some of which could result in your bank account being emptied, others could result in sensitive information being exposed and your accounts being hijacked. Then there is ransomware, which could be used to stop you from accessing your data (unless you have backups or pay the ransom payment).

More malicious websites are now being created than legitimate sites, so how can you stay safe online? One solution used by businesses and ISPs is the use of a web filter. A web filter can be configured to restrict access to certain categories of Internet content and block the majority of malicious websites.

While it is possible for businesses or ISPs to purchase appliances that sit between end users and the Internet, DNS filters allow the Internet to be filtered without having to purchase any hardware or install any software. So how does DNS filtering work?

How Does DNS Filtering Work?

DNS filtering – or Domain Name System filtering to give it its full title – is a technique of blocking access to certain websites, webpages, or IP addresses. DNS is what allows easy to remember domain names to be used – such as Wikipedia.com – rather than typing in very difficult to remember IP addresses – such as 198.35.26.96. DNS maps IP addresses to domain names.

When a domain is purchased from a domain register and that domain is hosted, it is assigned a unique IP address that allows the site to be located. When you attempt to access a website, a DNS query will be performed. Your DNS server will look up the IP address of the domain/webpage, which will allow a connection to be made between the browser and the server where the website is hosted. The webpage will then be loaded.

So how does DNS filtering work? With DNS filtering in place, rather than the DNS server returning the IP address if the website exists, the request will be subjected to certain controls. If a particular webpage or IP address is known to be malicious, the request to access the site will be blocked. Instead of connecting to a website, the user will be directed to a local IP address that will display a block page explaining that the site cannot be accessed.

This control could be applied 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 instance – would point their DNS to the service provider. That service provider maintains a blacklist of malicious webpages/IP addresses. If a site is known to be malicious, access to malicious sites will be blocked.

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

Will a DNS Filter Block All Malicious Websites?

Unfortunately, no DNS filtering solution will block all malicious websites, as in order to do so, a webpage must first be determined to be malicious. If a cybercriminal sets up a brand-new phishing webpage, there will be a delay between the page being created and it being checked and added to a blocklist. However, a DNS web filter will block the majority of malicious websites.

Can DNS Filtering be Bypassed?

The short answer is yes. Proxy servers and anonymizer sites could be used to mask traffic and bypass the DNS filter unless the chosen solution also blocks access to these anonymizer sites. An end user could also manually change their DNS settings locally unless they have been locked down. Determined individuals may be able to find a way to bypass DNS filtering, but for most end users, a DNS filter will block any attempt to access forbidden or harmful website content.

No single cybersecurity solution will allow you to block 100% of malicious websites or all NSFW websites, but DNS filtering should certainly be part of your cybersecurity defences as it will allow the majority of malicious sites and malware to be blocked.

If you have yet to implement a web filtering solution, are unhappy with your current provider, or you have questions about web filtering in the workplace, contact the TitanHQ team today and ask about WebTitan Cloud.