DNS works with a firewall by providing the domain name information that the firewall can use to make filtering decisions, particularly in the case of DNS firewalls or integrated DNS filtering features.
Firewalls act as a barrier between networks, controlling incoming and outgoing traffic based on predefined security rules. Traditionally, firewalls inspect traffic based on IP addresses, ports, and protocols. However, the Domain Name System (DNS) plays a crucial role in translating human-readable domain names (like example.com) into machine-readable IP addresses (like 192.168.1.1).
When a user tries to access a website or online service using its domain name, their device first performs a DNS query to resolve that domain name to an IP address. Firewalls, especially those with advanced security features like DNS filtering or dedicated DNS firewalls, can leverage this DNS resolution process to enhance security.
The Role of DNS Firewalls
According to the provided reference, a domain name system (DNS) firewall prevents users from going to malicious websites by offering protection against websites that could infect a computer or network with malware. This highlights a key way DNS interacts with firewalls: the firewall (or a component acting like one) inspects or controls DNS requests before the connection to the target IP address is even attempted.
Here's how this interaction typically works:
- DNS Query Interception: The firewall or a designated DNS server controlled by the firewall intercepts DNS queries originating from the internal network.
- Policy Check: The firewall checks the requested domain name against its policies or threat intelligence databases. These policies can include:
- Lists of known malicious domains (e.g., associated with malware, phishing, command and control servers).
- Lists of blocked domains based on categories (e.g., social media, gambling, specific websites) for content filtering or policy enforcement.
- Lists of allowed domains.
- Action Based on Policy:
- If the domain is malicious or blocked: The firewall blocks the DNS query, preventing the user's device from getting the IP address. Instead, it might return a "non-existent domain" response or redirect the user to a block page. Admins can also use firewall configuration to block sites they don't want employees to visit. This directly utilizes the DNS name as the basis for the block rule.
- If the domain is allowed or uncategorized: The firewall permits the DNS query to proceed to a recursive DNS server to get the correct IP address.
- Traffic Filtering: Even after the DNS resolution is allowed, traditional firewall rules can still inspect the subsequent IP-based traffic (e.g., blocking specific ports or protocols to that IP), but blocking at the DNS layer is proactive and prevents the connection from starting.
Benefits of Integrating DNS and Firewall Policies
Integrating DNS awareness into firewall capabilities offers several advantages:
- Proactive Threat Prevention: Blocking access at the DNS layer stops connections to malicious sites before any harmful content can be downloaded or executed.
- Granular Control: Policies can be based on domain names or categories, which are often more intuitive and easier to manage than lists of ever-changing IP addresses.
- Reduced Alert Fatigue: Blocking known threats at the DNS level can reduce the number of alerts generated by later-stage security controls.
- Policy Enforcement: Admins can enforce acceptable use policies by blocking specific types of websites based on their domain names.
Summary Table: How DNS Information is Used by Firewalls
| Feature/Concept | DNS Interaction | Firewall Action |
|---|---|---|
| DNS Firewall | Intercepts DNS query for a domain name | Blocks query if domain is malicious or explicitly blocked |
| Content Filtering | Uses domain names to categorize websites | Blocks or allows access based on domain category |
| Threat Intelligence Feeds | Compares requested domain to known bad domains | Blocks query if domain matches a threat feed entry |
| Application Control | May identify applications based on DNS requests | Enforces policies on specific applications (e.g., social media) identified by their domain names |
In essence, firewalls use DNS information to add another layer of defense, shifting from solely inspecting IP traffic to also controlling which IP addresses users can discover and connect to based on their associated domain names.
