200-201 Network Intrusion Analysis Practice Question
An analyst monitoring an internal network observes a host sending a large number of TCP segments with the URG flag set and a non-zero urgent pointer, but the urgent pointer value does not point to actual urgent data. The destination host appears to be processing the data normally. Which explanation best describes what the analyst is observing?
⚠ Common exam trap
The trap here is assuming URG always indicates legitimate Telnet break handling, when in practice URG with a meaningless pointer is a known evasion and covert-channel technique.
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
✓
An attacker is using the TCP urgent pointer as a covert signaling mechanism or IDS evasion technique
The TCP urgent pointer is rarely used by modern applications and is inconsistently handled by IDS engines and operating systems. Attackers exploit this by setting URG with a pointer that does not correspond to real urgent data, using the flag pattern as a covert signal to a cooperating peer or to desynchronize the IDS's view of the stream while the actual data is processed normally by the target.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The host is performing a legitimate Telnet session where urgent data indicates a break command
Why it's wrong here
Telnet does use the urgent pointer to deliver the SYNCH sequence for the break function, but that occurs in interactive Telnet sessions and points to actual urgent data. Here the urgent pointer does not point to real urgent data and the host sends many such segments, which is inconsistent with normal Telnet break handling.
- ✗
The host is experiencing a TCP window zero condition caused by application backpressure
Why it's wrong here
A zero-window condition is signaled by the window size field being set to zero, not by the URG flag or urgent pointer. The scenario describes URG with a non-zero urgent pointer and normal data processing, which is unrelated to flow control backpressure, so window zero does not explain the observation.
- ✗
The host is retransmitting segments because the receiver's ACKs are being lost in transit
Why it's wrong here
Retransmissions are triggered by missing ACKs and duplicate ACKs, and the retransmitted segments would carry the same sequence numbers as the originals. The scenario describes many segments with URG set and a meaningless urgent pointer, not duplicate sequence numbers, so retransmission is not the correct explanation.
- ✓
An attacker is using the TCP urgent pointer as a covert signaling mechanism or IDS evasion technique
Why this is correct
Because many IDS engines and applications ignore or mishandle the URG flag and urgent pointer, attackers can abuse them as a side channel or to desynchronize inspection. Setting URG with a meaningless urgent pointer while still delivering normal data lets the attacker signal a cooperating peer or confuse the IDS without disrupting the actual TCP stream.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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