Question 36 of 464
N10-009 Network Security Practice Question
A security analyst is investigating a potential data exfiltration. The analyst notices that a server is sending DNS queries to an external IP address on TCP port 53, and the DNS responses are unusually large. The server is not a DNS server. Which technique is most likely being used?
⚠ Common exam trap
CompTIA often tests the distinction between DNS amplification (a DDoS attack using UDP reflection) and DNS tunneling (a covert channel using TCP or UDP for data exfiltration), and the trap here is that candidates see 'large responses' and immediately think amplification, ignoring the TCP port 53 and non-DNS server context.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
DNS tunneling
DNS tunneling encodes non-DNS data (e.g., exfiltrated files) within DNS queries and responses, often using TCP port 53 to bypass firewalls. The unusually large responses are a hallmark of tunneled data being returned in DNS payloads, and the fact that the server is not a DNS server strongly indicates it is being used as a client for covert data transfer.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
DNS amplification attack
Why it's wrong here
DNS amplification is a DDoS technique where an attacker sends small queries with spoofed IPs to generate large responses; here the server is sending queries to an external IP, and it's sending queries, not receiving them with spoofed source.
When this WOULD be correct
A DNS amplification attack would be correct if the question described a server sending small DNS queries to open resolvers with a spoofed source IP (the victim), resulting in large responses flooding the victim.
- ✓
DNS tunneling
Why this is correct
DNS tunneling leverages the DNS protocol to exfiltrate data or establish command-and-control channels by encoding arbitrary data within DNS queries and responses. Attackers often embed data in subdomain names of queries or within resource record fields of responses, making it appear as legitimate DNS traffic. Indicators include unusually large DNS response sizes, frequent queries to uncommon domains, or the unexpected use of TCP port 53 for data transfer, which is typically reserved for zone transfers.
- ✗
DNS zone transfer
Why it's wrong here
A DNS zone transfer is a legitimate process where a secondary DNS server requests and receives a complete copy of a DNS zone file from a primary authoritative DNS server. This mechanism, typically using TCP port 53, ensures synchronization of DNS records across multiple servers for redundancy and load balancing. It is a controlled replication process between DNS servers and is not designed for, nor would it typically be used by, a non-DNS server to exfiltrate arbitrary data to an external IP address.
When this WOULD be correct
A question describing a secondary DNS server failing to synchronize with a primary server, with large zone data transfers occurring over TCP port 53, would make DNS zone transfer the correct answer.
- ✗
DNS cache poisoning
Why it's wrong here
DNS cache poisoning involves an attacker injecting fraudulent DNS records into a recursive DNS resolver's cache, causing it to return incorrect IP addresses for legitimate domain names. This misdirection can redirect users to malicious websites or facilitate man-in-the-middle attacks, rather than directly exfiltrating data from a compromised server. The attack focuses on manipulating the resolver's cached entries, not on a compromised server actively sending numerous queries or large responses containing exfiltrated data.
When this WOULD be correct
A question describing a user being redirected to a malicious site after a DNS resolver returns incorrect IP addresses, with no mention of data exfiltration or large responses, would make DNS cache poisoning correct.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓DNS tunnelingCorrect answer▾
Why this is correct
DNS tunneling leverages the DNS protocol to exfiltrate data or establish command-and-control channels by encoding arbitrary data within DNS queries and responses. Attackers often embed data in subdomain names of queries or within resource record fields of responses, making it appear as legitimate DNS traffic. Indicators include unusually large DNS response sizes, frequent queries to uncommon domains, or the unexpected use of TCP port 53 for data transfer, which is typically reserved for zone transfers.
✗DNS amplification attackWrong answer — click to see why▾
Why this is wrong here
A DNS amplification attack uses UDP, not TCP, and involves sending small queries that generate large responses to a victim, not to an external IP from a server. The server here is the source, not the target.
★ When this WOULD be the correct answer
A DNS amplification attack would be correct if the question described a server sending small DNS queries to open resolvers with a spoofed source IP (the victim), resulting in large responses flooding the victim.
Why candidates choose this
Candidates may confuse 'unusually large DNS responses' with amplification, but they overlook the TCP port 53 and the server initiating queries to an external IP, which points to tunneling instead.
✗DNS zone transferWrong answer — click to see why▾
Why this is wrong here
DNS zone transfer is used to replicate DNS databases between authoritative servers, not for data exfiltration. The scenario involves a non-DNS server sending queries to an external IP, which is characteristic of tunneling, not zone transfer.
★ When this WOULD be the correct answer
A question describing a secondary DNS server failing to synchronize with a primary server, with large zone data transfers occurring over TCP port 53, would make DNS zone transfer the correct answer.
Why candidates choose this
Candidates may confuse large DNS responses with zone transfers, or think that any unusual DNS traffic on TCP port 53 indicates a zone transfer, overlooking the data exfiltration context.
✗DNS cache poisoningWrong answer — click to see why▾
Why this is wrong here
DNS cache poisoning involves corrupting a DNS resolver's cache with false records, not exfiltrating data via large DNS responses. The scenario describes data exfiltration, not cache manipulation.
★ When this WOULD be the correct answer
A question describing a user being redirected to a malicious site after a DNS resolver returns incorrect IP addresses, with no mention of data exfiltration or large responses, would make DNS cache poisoning correct.
Why candidates choose this
Candidates may confuse DNS cache poisoning with DNS tunneling because both involve DNS abuse, but cache poisoning focuses on redirection, not data exfiltration via response size.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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Last reviewed: Jun 30, 2026
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