ANS-C01 Network Management and Operations Practice Question
This ANS-C01 practice question tests your understanding of network management and operations. 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.
A company runs a critical application on EC2 instances in an Auto Scaling group across two Availability Zones. The application is fronted by an Application Load Balancer (ALB). The network team recently migrated from a transit VPC to a transit gateway for inter-VPC connectivity. After the migration, users experience intermittent connectivity failures. The team checks the ALB target group and sees that health checks are passing. However, from an EC2 instance in the same VPC, they can reach the ALB but not the application. They notice that the application sends traffic to an internal DNS server that is in a different VPC, and the application depends on that DNS resolution. The transit gateway route tables are configured to propagate routes from attached VPCs. The DNS server is reachable from the application VPC over the transit gateway. What is the MOST likely cause of the intermittent failures?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The DNS server returns different IP addresses for the same DNS name, and some IPs are not reachable due to route table misconfiguration.
If the DNS server returns different IP addresses for the same DNS name due to DNS round-robin or time-to-live (TTL) caching, the application may get an IP address that is not reachable (e.g., from a different VPC or a terminated instance). The health check may pass because the target group health check uses the ALB's IP, not the application's DNS resolution. Option A is plausible but less likely because the DNS server is reachable. Option B could cause total failure, not intermittent. Option D would affect all traffic, not just intermittent.
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.
✗
The transit gateway route tables have a blackhole route for the DNS server's VPC.
Why it's wrong here
Would cause persistent failure, not intermittent.
✗
The Auto Scaling group is scaling in and out frequently, causing application instances to be terminated during DNS resolution.
Why it's wrong here
Would cause timeouts during scaling events but not intermittent in steady state.
✓
The DNS server returns different IP addresses for the same DNS name, and some IPs are not reachable due to route table misconfiguration.
Why this is correct
DNS changes with TTL can cause intermittent reachability to specific IPs.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The ALB security group does not allow traffic from the application instances on the ephemeral ports.
Why it's wrong here
Would affect health checks and all traffic, not intermittent.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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 ANS-C01 NAT questions on configuration and troubleshooting.
Network Management and Operations — This question tests Network Management and Operations — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The DNS server returns different IP addresses for the same DNS name, and some IPs are not reachable due to route table misconfiguration. — If the DNS server returns different IP addresses for the same DNS name due to DNS round-robin or time-to-live (TTL) caching, the application may get an IP address that is not reachable (e.g., from a different VPC or a terminated instance). The health check may pass because the target group health check uses the ALB's IP, not the application's DNS resolution. Option A is plausible but less likely because the DNS server is reachable. Option B could cause total failure, not intermittent. Option D would affect all traffic, not just intermittent.
What should I do if I get this ANS-C01 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 ANS-C01 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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