200-201 Security Monitoring Practice Question
A security engineer is setting up a Snort rule to detect FTP traffic where the source IP is not from the internal network. Which Snort rule header correctly specifies the action, protocol, source, and destination?
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
✓
alert tcp !$HOME_NET any -> any 21
The correct Snort rule header format is: alert tcp !$HOME_NET any -> any 21. It alerts on TCP traffic from any IP not in $HOME_NET to any destination on port 21 (FTP).
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
alert tcp !$HOME_NET any -> any 21
Why this is correct
The ! negation operator excludes the internal network, focusing on external sources.
- ✗
alert tcp $HOME_NET any -> any 21
Why it's wrong here
This would alert on FTP traffic from internal IPs, the opposite of what is needed.
- ✗
alert tcp any any -> any 21
Why it's wrong here
This rule alerts on all FTP traffic, not just from external sources.
- ✗
alert udp any any -> any 21
Why it's wrong here
FTP uses TCP, not UDP.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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