The answer is to block the source IP (203.0.113.5) at the firewall. This is the most appropriate action for repeated VPN authentication failures because such a pattern strongly suggests a brute-force attack or a persistent misconfiguration, and blocking the offending source IP immediately halts the threat at the network perimeter. On the Certified in Risk and Information Systems Control CRISC exam, this scenario tests your ability to apply risk response techniques—specifically, the principle of reducing likelihood by eliminating the attack vector—rather than ignoring the event, overreacting with broad policy changes, or jumping to unverified conclusions. A common trap is to consider updating authentication policies for all sources, but that would disrupt legitimate users and is disproportionate to a single hostile IP. Remember the memory tip: “Block the bot, not the whole lot”—always isolate the specific source before escalating controls.
CRISC Risk and Control Monitoring and Reporting Practice Question
This CRISC practice question tests your understanding of risk and control monitoring and reporting. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Exhibit
Feb 15 09:23:45 fw01 %ASA-4-722041: Tunnel negotiation failed to/from IP 203.0.113.5 to 198.51.100.20 due to authentication failure.
Feb 15 09:24:12 fw01 %ASA-4-722041: Tunnel negotiation failed to/from IP 203.0.113.5 to 198.51.100.20 due to authentication failure.
Feb 15 09:24:50 fw01 %ASA-4-722041: Tunnel negotiation failed to/from IP 203.0.113.5 to 198.51.100.20 due to authentication failure.
Refer to the exhibit. A security analyst reviews firewall logs and sees repeated authentication failures for VPN tunnel attempts between two IP addresses. What is the MOST appropriate action?
Feb 15 09:23:45 fw01 %ASA-4-722041: Tunnel negotiation failed to/from IP 203.0.113.5 to 198.51.100.20 due to authentication failure.
Feb 15 09:24:12 fw01 %ASA-4-722041: Tunnel negotiation failed to/from IP 203.0.113.5 to 198.51.100.20 due to authentication failure.
Feb 15 09:24:50 fw01 %ASA-4-722041: Tunnel negotiation failed to/from IP 203.0.113.5 to 198.51.100.20 due to authentication failure.
A
Block the source IP (203.0.113.5) at the firewall.
Blocking the attacking IP mitigates threat.
B
Contact the destination IP owner to verify credentials.
Why wrong: Source is likely the attacker.
C
Update the VPN policy to allow all authentication methods.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Block the source IP (203.0.113.5) at the firewall.
Option B is correct because repeated authentication failures indicate a potential brute-force attack or misconfiguration. Blocking the source IP can prevent further attempts. Option A is wrong because ignoring may allow continued attack. Option C is wrong because updating policy for all sources is too broad. Option D is wrong because contacting the destination without investigation is premature.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Block the source IP (203.0.113.5) at the firewall.
Why this is correct
Blocking the attacking IP mitigates threat.
Related concept
Static NAT maps one inside address to one outside address.
✗
Contact the destination IP owner to verify credentials.
Why it's wrong here
Source is likely the attacker.
✗
Update the VPN policy to allow all authentication methods.
Why it's wrong here
Not addressing root cause.
✗
Ignore the logs as routine failed attempts.
Why it's wrong here
Repeated failures warrant action.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CRISC NAT questions on configuration and troubleshooting.
Risk and Control Monitoring and Reporting — This question tests Risk and Control Monitoring and Reporting — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Block the source IP (203.0.113.5) at the firewall. — Option B is correct because repeated authentication failures indicate a potential brute-force attack or misconfiguration. Blocking the source IP can prevent further attempts. Option A is wrong because ignoring may allow continued attack. Option C is wrong because updating policy for all sources is too broad. Option D is wrong because contacting the destination without investigation is premature.
What should I do if I get this CRISC question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related CRISC NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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