Cisco CyberOps Associate (CBROPS) 200-201Security ConceptsMedium
A security analyst is reviewing a firewall's configuration rules. One rule permits all outbound traffic from the internal network to external destinations on TCP port 53. Another rule permits inbound traffic on TCP port 80 to a web server. Which core network security concept is being demonstrated by explicitly defining allowed traffic and implicitly denying all other traffic?
- AImplicit Deny
- BDefense in Depth
- CNetwork Segmentation
- DPrinciple of Least Privilege
Show answer & explanationAnswer & explanation
Correct answer: A. Implicit Deny
Implicit deny is a core security principle in firewalls and access control lists (ACLs) where, by default, any traffic not explicitly permitted by a rule is automatically denied. The scenario describes specific allowed traffic, implying that anything else would be blocked.
Why the other options are wrong
- B. Defense in depth uses multiple layers of security, not a single firewall rule concept.
- C. Network segmentation divides networks, but implicit deny is a rule-based principle within a segment or firewall.
- D. Least privilege applies to user/process permissions, not firewall traffic flow.
Implicit Deny
A security principle, most commonly applied in firewalls and access control lists (ACLs), where any access or traffic that is not explicitly permitted by a rule is automatically denied. This ensures that only authorized actions or communications are allowed.
- Last rule in most firewall rule sets (invisible).
- Ensures security by default, preventing unapproved access.
- Opposite of 'implicit allow' (which is highly insecure).
Memory trick: Implicit Deny is like having a 'No Entry' sign everywhere unless there's a specific 'Entry Permitted' sign.