One of the basic services that firewalls (both next-generation firewalls and Unified Threat Management appliances) provide is the ability to block users from connecting to servers that host malware. There are different ways to do this, and each one has advantages and drawbacks. Our Sr. Technical Product Manager, Ricardo Arroyo, recently wrote a guest post for Help Net Security explaining some of these methods and why he believes filtering based on Domain Name System (DNS) is a good fit for many organizations.
Organizations can block malicious sites based on IP address, but a single IP address can host multiple services and multiple domain names can map to the same IP address. In practice, this method blocks legitimate sites along with the malicious ones. Filtering based on full URLs is more granular, but URLs are specific to each application protocol (HTTP and FTP for example), so this type of filtering requires much more work on the back end. DNS filtering sits in the sweet spot between these two options; not too broad as to block legitimate sites by accident, but not too much extra work for IT either. Here’s an excerpt from the article:
“For example, regardless of whether you read your email using a thick client like Outlook or use a web UI like Gmail, clicking on a malicious link will result in the same resolution of the same name. The same goes for documents. Clicking on a malicious link in Acrobat Reader or Microsoft Word results in the same resolution of the same name regardless of document type or application. That means DNS-level filtering will block malicious links in all of these scenarios without needing to be customized to the specific application or protocol in use. With workers accessing corporate data from multiple devices, checking email on their phones and using applications that IT might not even know about, the flexibility provided by DNS filtering is extremely useful.”
Read Ricardo’s full article on Help Net Security for more information on malware filtering options and how to fit DNS filtering into a larger security setup. You can read more about WatchGuard’s malware filtering services here and learn about other DNS security issues on a recent episode of The 443 podcast.