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200-201 Practice Question: Which THREE types of network traffic anomalies…
Which THREE types of network traffic anomalies are strong indicators of a data exfiltration attempt?
⚠ Common exam trap
Cisco often tests the distinction between network anomalies that indicate data exfiltration versus those that indicate denial-of-service or reconnaissance; the trap here is confusing a SYN flood (Option D) with a covert channel, when exfiltration requires established, often stealthy, outbound connections.
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
✓
TCP connections with unusual port numbers (e.g., using SSH on port 80)
Option A is correct because tunneling protocols over unexpected ports—such as SSH on TCP 80 or other non-standard port mappings—are a classic exfiltration technique that evades port-based firewall rules and blends with allowed traffic. Option B is correct because DNS exfiltration encodes stolen data in long or high-entropy subdomain labels (e.g., base32/base64 chunks) sent to an attacker-controlled authoritative name server, which is a well-known covert channel. Option E is correct because a large outbound volume to one external destination during off-hours deviates from normal baseline behavior and matches the bulk-transfer pattern of data exfiltration. Option C is not a strong exfiltration indicator; frequent ARP requests typically point to Layer 2 issues such as ARP scanning, misconfiguration, or ARP spoofing on the local segment. Option D is not a strong exfiltration indicator either; many SYNs without ACKs indicate SYN scanning or a SYN flood denial-of-service, not outbound data theft.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
TCP connections with unusual port numbers (e.g., using SSH on port 80)
Why this is correct
Unusual port usage signals protocol tunnelling, where attackers hide exfiltration inside permitted ports to bypass egress filtering. SSH over port 80 evades firewalls expecting HTTP, letting stolen data leave disguised as web traffic. This satisfies the stem's requirement for a strong exfiltration indicator, since legitimate services rarely bind to mismatched ports.
- ✓
DNS queries with long subdomains encoding data
Why this is correct
DNS tunnelling hides stolen data inside the subdomain labels of otherwise legitimate-looking queries. Because each label can carry encoded payload, unusually long or high-entropy subdomains to a single domain reveal exfiltration that would otherwise blend into permitted DNS traffic.
- ✗
Frequent ARP requests from a single host
Why it's wrong here
Frequent ARP requests from one host indicate layer-2 address resolution churn, such as scanning or ARP spoofing, not bulk data leaving the network. It is tempting because it is anomalous host behaviour, but it would be correct when investigating local subnet reconnaissance or cache-poisoning, not exfiltration volume.
- ✗
High number of SYN packets without corresponding ACKs
Why it's wrong here
SYN packets without matching ACKs indicate half-open connections, typical of SYN flooding or port scanning, not outbound data transfer. It is tempting because it is a clear traffic anomaly, but it would be correct when diagnosing denial-of-service or scan activity, not exfiltration.
- ✓
Large amounts of outbound traffic to a single destination during non-business hours
Why this is correct
Exfiltration requires transferring data outbound, so a sustained volume spike to one external destination outside working hours exposes the theft. The single-destination and off-hours constraints distinguish deliberate extraction from normal daytime backup or browsing patterns.
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Same concept, more angles
1 more way this is tested on 200-201
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Which TWO types of network traffic should be analyzed to detect a data exfiltration attempt via HTTP? (Choose two.)
easy- A.ICMP echo requests
- ✓ B.HTTP request headers
- ✓ C.HTTP request body
- D.DNS query responses
- E.TCP three-way handshake
Why B: HTTP request headers (B) are correct because exfiltration over HTTP often hides data in custom, non-standard, or unusually long header fields (e.g., Cookie, User-Agent, Referer, X-* headers), and inspecting them reveals anomalous values, oversized fields, or encoded payloads that indicate data being smuggled out. HTTP request body (C) is correct because the body is the primary carrier for exfiltrated content in POST/PUT requests, so examining it for large volumes, base64/hex-encoded blobs, or sensitive data patterns is essential to detect the theft. ICMP echo requests (A) are not HTTP traffic and are typically used for reachability testing or covert channels via ping payloads, not HTTP exfiltration. DNS query responses (D) relate to DNS tunneling/exfiltration, a separate protocol channel, not HTTP. The TCP three-way handshake (E) only establishes the connection (SYN, SYN-ACK, ACK) and carries no application-layer payload, so it cannot reveal exfiltrated data.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-201 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-201 exam.