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200-201 Practice Question: Which TWO of the following are common indicators…
Which TWO of the following are common indicators of a denial-of-service (DoS) attack?
⚠ Common exam trap
Cisco often tests the distinction between a single-source DoS attack (option D) and a distributed DDoS attack (options B and C), where candidates may confuse the gradual increase from multiple locations as a DoS indicator instead of recognizing it as a DDoS characteristic.
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
✓
A sudden increase in traffic from a single source IP address
A sudden increase in traffic from a single source IP address is a classic indicator of a direct DoS attack, where the attacker uses a single compromised host to flood the target with packets, overwhelming its resources. This contrasts with a distributed denial-of-service (DDoS) attack, which uses multiple sources. The abrupt spike in volume from one IP is a clear anomaly that network monitoring tools flag as a potential DoS event.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A low level of network utilization on the target server
Why it's wrong here
DoS attacks increase utilization, not decrease.
- ✗
A gradual increase in traffic from multiple geographic locations
Why it's wrong here
This may be normal traffic growth or a marketing campaign.
- ✗
A high number of DNS queries from diverse source IPs
Why it's wrong here
This could be a DDoS, but the question asks for DoS (single source).
- ✓
A sudden increase in traffic from a single source IP address
Why this is correct
This indicates a potential DoS attack from that IP.
- ✓
A large number of incomplete TCP connections (SYN packets without ACK)
Why this is correct
This is characteristic of a SYN flood DoS attack.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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