350-701 Question #735: Real Exam Question with Answer & Explanation

The correct answer is C. inspecting the DNS traffic. Cisco Secure Firewall helps mitigate data exfiltration risks by inspecting DNS traffic for anomalies or unauthorized data tunneling. Many advanced persistent threats use DNS tunneling to covertly steal sensitive information from an organization's network.

Submitted by katya_ua· Mar 30, 2026Network Security

Question

How does a Cisco Secure Firewall help to lower the risk of exfiltration techniques that steal customer data?

Options

Ablocking UDP port 53
Bblocking TCP port 53
Cinspecting the DNS traffic
Dencrypting the DNS communication

Explanation

Cisco Secure Firewall helps mitigate data exfiltration risks by inspecting DNS traffic for anomalies or unauthorized data tunneling. Many advanced persistent threats use DNS tunneling to covertly steal sensitive information from an organization's network.

Common mistakes.

A. Blocking UDP port 53 would prevent legitimate DNS resolution for most internet communications, disrupting normal network operations rather than specifically targeting data exfiltration within DNS. This is too broad and disruptive.
B. Blocking TCP port 53 would prevent legitimate DNS zone transfers and might affect some specific DNS services, but it is not a primary mechanism to detect and stop data exfiltration embedded within standard DNS queries and responses.
D. Encrypting DNS communication, such as DNS over HTTPS (DoH) or DNS over TLS (DoT), makes it difficult for a firewall to inspect the DNS payload for malicious content, thereby hindering the detection of DNS-based exfiltration rather than lowering its risk through inspection.

Concept tested. DNS tunneling exfiltration detection

Reference. https://www.cisco.com/c/en/us/products/security/dns-security/what-is-dns-tunneling.html

Topics

#Data Exfiltration#DNS Security#Firewall Inspection#Application Layer Security

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