Category-based filtering is a way to control internet access by grouping websites into groups then applying rules to them. It works at the DNS level and is commonly used for:
- Security: Blocking malware, phishing, and harmful sites.
- Workplace Productivity: Restricting access to distracting websites like social media or streaming during work hours.
- Child Safety: Creating safer online spaces for kids by blocking adult content and other harmful material.
Here’s how it works:
- Websites (domains) are categorized based on their content.
- A DNS filtering service checks each website request made by a user on the network.
- Depending on the rules, access is either allowed or blocked.
This system is flexible, allowing organizations to customize rules for different needs, like schools, homes, or businesses. It also supports dynamic updates to keep up with new threats and content changes. This type of filtering is extremely helpful in creating and enforcing Acceptable Use Policies on the networks internet.
How Content Filtering Categories Work
With content-based content filtering domains are grouped into categories using advanced systems that evaluate factors like:
- The site’s content and overall context
- Proprietary data from filtering providers
- Intelligence from third-party sources
- Feedback from user communities
For instance, a platform like Netflix would typically fall under “Streaming Video”, while LinkedIn might be categorized under both “Business and Economy” and “Social Networking”. This layered classification allows for more precise control over access.
Once categorized, DNS filtering applies the appropriate rules to manage access.
DNS Filtering Process
Here’s how DNS filtering works after a domain is categorized: :
- A user types a domain or clicks a link.
- The DNS filter intercepts the request before it reaches its destination.
- The system checks the domain against its database.
- Based on the organization’s policies, the filter either:
- Grants access by resolving the domain to its IP address, or
- Blocks access by refusing to resolve the domain..
DNS filtering gives you the ability to filter bad or unwanted content at the network level. Because it works at the network level it is agnostic to the Operating System (OS) or application (e.g., app or browser) being used.
Common Category Types
Content filtering systems organize websites into categories based on risk and type. These categories help enforce security and productivity policies:
| Risk Level | Category Examples | Common Applications |
|---|---|---|
| High Risk | Malware, Phishing, Botnets | Security measures |
| Workplace Policy | Social Media, Gaming, Streaming | Managing productivity |
| Compliance | Adult Content, Gambling, Weapons | Meeting legal standards |
| Custom | Custom URLs/IPs | Tailored organizational needs |
Organizations can fine-tune these categories to match their specific requirements. Here at CleanBrowsing we offer 23+ different predefined categories and growing.
The success of this approach depends on keeping the categorized databases up to date. We dive deeper into how our categorization works and our engine (i.e., Categorify) in our post – How CleanBrowsing Categorify Works.
Advantages of Category Filtering
Category filtering goes beyond just organizing risks – it provides targeted benefits that enhance both security and productivity.
Security Protection
Category filtering helps shield organizations from cyber threats by blocking access to high-risk websites. Sites associated with malware, phishing, torrents, and parked domains are automatically restricted, reducing the chances of malware infections and social engineering attacks.
Workplace Focus
Research shows that 58% of employees spend over four hours a week on non-work-related websites, and 26% exceed seven hours. This has led 89% of companies to block such distractions. By restricting access to non-work content while keeping essential business resources available, category filtering helps create a more focused work environment. The result? Less wasted time, reduced bandwidth usage, and more responsible internet habits.
Flexible Control Options
Modern category filtering solutions allow for custom policies tailored to different user groups, schedule-based access rules, remote deployment options, block bypass for authorized personnel, and real-time policy updates. This level of control ensures security without compromising access to necessary resources.
Selecting a Filter Service
When choosing a filtering solution, it’s important to match it with your specific needs. For schools, compliance with CIPA is a must, while businesses often require detailed control over accessible content in the workplace. Look for options that offer easy management, integration with your systems, and the ability to tailor filtering categories.
Here are some key factors to consider:
- Number and flexibility of predefined categories
- Real-time monitoring and reporting tools
- Quality of customer support and training resources
- Deployment options (cloud-based or on-premises)
- Cost and ability to scale as your needs grow
After selecting a service, proceed to configure your deployment and set up filter rules.
Setting Filter Rules
To implement category filtering effectively, start with a clear plan. Decide whether you need protection at the router level or directly on individual devices.
For DNS-based filtering, follow these steps:
- Choose deployment at the router or device level.
- Enter the DNS addresses provided by your chosen filtering service.
- Confirm proper DNS routing using tools like dnsleaktest.com.
Once set up, make it a habit to check the performance of your DNS-based filtering regularly.
Common Problems and Limits
Filtering Accuracy Issues
Category-based filtering can sometimes block legitimate content or fail to catch harmful material. To address this, modern systems use advanced algorithms and layered methods. These approaches aim to reduce errors like mistakenly flagging educational or scientific resources (over-blocking) or allowing harmful content to bypass filters (under-blocking).
HTTPS and Privacy
The rise of HTTPS encryption has made content filtering more complex. Since most websites now use HTTPS, including those with ads, filtering can become less effective unless specific measures are taken. Two common methods for managing HTTPS traffic include:
| Method | How It Works | Considerations |
|---|---|---|
| Certificate Substitution | Installs root certificates to inspect encrypted traffic | Requires extra setup for apps that don’t trust user-installed certificates |
| SNI Analysis | Inspects Server Name Indication without decrypting traffic | Less intrusive but offers limited filtering capabilities |
To improve HTTPS filtering, organizations should:
- Regularly test HTTPS connection quality
- Install and configure root certificates correctly
- Adjust Firefox settings (e.g., set
security.enterprise_roots.enabledtotrue) for system-level certificate trust
New Content Management
Managing constantly changing web content is another challenge for category-based filtering systems. Modern tools combine various technologies to handle new content types and threats. Effective strategies include:
- Real-time Content Analysis: Scans page text, images, and other elements to detect harmful material
- AI-Based Classification: Uses machine learning to improve categorization accuracy
- Frequent Policy Updates: Ensures filtering rules stay aligned with evolving internet trends
Organizations can strengthen their filtering systems by integrating detailed logging and monitoring tools and tailoring policies for different user groups and locations. CleanBrowsing for example has an Activity panel that gives you a 7 day view of activity on your network. For best practice, however, administrators should consider retaining logs longer and you can achieve this by
Category-based filtering helps create safer and more efficient online spaces by controlling web access through DNS-level, policy-based categorization.
Here’s how it makes a difference:
| Benefit Type | Impact |
|---|---|
| Security | Blocks harmful websites, phishing attempts, and suspicious domains |
| Productivity | Limits access to unnecessary sites and optimizes bandwidth usage |
| Compliance | Supports regulatory requirements, like CIPA, for schools |
| Customization | Allows tailored filtering rules for different user groups |
Platforms like CleanBrowsing handle over 355 billion requests each month across 70 data centers, showcasing the scale and dependability of today’s filtering systems.
To stay ahead of threats, it’s important to regularly update filtering rules, integrate them with other cybersecurity tools, and keep an eye on usage patterns. Schools, for instance, rely on these filters to comply with CIPA and ensure secure learning environments.