Definition
Blocking DNS Network Traffic based on criteria such as IP address, domain name, or DNS query type.
How it works
Rules are implemented that filter DNS queries using criteria such as:
For example, a DNS policy can be created for blocking DNS queries for FQDNs that have been identified as unauthorized.
- Client subnet
- Type of network protocol used in query
- Fully qualified domain name (FQDN) of record in the query
- DNS Server IP address that received the DNS request
- Type of DNS record being queried
- Time of day the query is received
- Size of the response
Considerations
- Implementation considerations for DNS filtering policies to avoid over-blocking or under-blocking domains.
- Continuous maintenance of unauthorized domain lists is needed to keep up to date with possible site content changes.
- File sharing or content delivery networks may require other filtering techniques that are more fine-grained (URL blocking).
- Access to malicious websites or other network resources directly by IP instead of by DNS record, or after alteration of local DNS hosts file, may not result in DNS network traffic.
Implementation perspective
DNS Denylisting should be treated as a technical defensive capability rather than a product checkbox. In practice, teams should define the protected scope, the conditions under which the technique acts, and the observable evidence that demonstrates the intended behavior. For this technique, likely engineering context includes DNS Network Traffic.
Use the technique to create a logical or physical boundary that limits access, execution, communication, or movement.
Questions to ask
- What is being isolated, from whom or what, and under which conditions?
- Which flows or operations remain explicitly allowed across the boundary?
- What happens when the isolation mechanism fails or loses policy context?
- How is the boundary tested for alternate paths, bypasses, and unintended dependencies?
Evidence and validation
- Architecture and data-flow diagrams showing the isolation boundary
- Policy, rule, or configuration exports from enforcing components
- Tests of allowed, denied, and failure-state behavior
- Monitoring evidence for boundary violations and policy changes
Common failure patterns
- The intended boundary has undocumented alternate paths or inherited trust relationships.
- Rules accumulate without ownership, review, or removal of obsolete exceptions.
- Isolation is assumed from network location while application, identity, or management paths remain open.
This implementation perspective is original Bare Metal Cyber educational content. It does not replace the official D3FEND definition or establish that a specific product implements the technique.
Technique hierarchy
Top-level family
Parent techniques
Artifacts and ontology entities
These relationships describe how D3FEND connects a defensive technique to artifacts or other ontology entities. They describe graph semantics, not a product certification.
Explicit technique relationships
Show inferred artifact relationship paths (1)
ATT&CK Enterprise mitigation relationships
These links come from the D3FEND ontology’s ATT&CK mitigation mapping. They help users navigate between the knowledge bases and do not guarantee mitigation effectiveness.
D3FEND note: M1021 scope is broad, touches on an wide variety of techniques in d3fend.
Offensive-technique relationships
These relationships are generated from D3FEND graph paths and are explicitly experimental. They should be treated as hypotheses for defensive analysis—not as proof that the technique prevents, detects, or removes an offensive behavior.
ATT&CK Enterprise (2)
Authoritative sources
- Open this technique on the official D3FEND website ↗
- Open the official ontology resources ↗
- Use DNS Policy for Applying Filters on DNS Queries ↗Microsoft · UserManualReference
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