ANS-C01 Network Design Practice Question
A company has a VPC with a CIDR of 10.0.0.0/16. They have set up a VPC peering connection with another VPC (CIDR 172.16.0.0/16). The route tables are configured correctly. However, instances in the first VPC cannot communicate with instances in the peered VPC. The security groups and network ACLs are configured to allow all traffic. What is the most likely cause?
⚠ Common exam trap
The ANS-C01 exam often tests the misconception that route tables and security groups are the only requirements for VPC peering communication, while the subtle DNS resolution setting is a common overlooked prerequisite.
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
✓
The DNS resolution settings for the VPC peering connection are not enabled.
The most likely cause is that the VPC peering connection's DNS resolution settings are not enabled. While basic IP connectivity does not require DNS, if instances are using private DNS hostnames (a common default), DNS queries for the peered VPC will fail unless this setting is enabled. Since the route tables are correctly configured, security groups allow all traffic, and CIDR ranges do not overlap, the DNS resolution setting is the only remaining plausible cause from the options.
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 DNS resolution settings for the VPC peering connection are not enabled.
Why this is correct
When VPC peering is created, DNS resolution must be enabled to allow DNS hostnames to resolve across the peering connection.
- ✗
The route tables in the VPCs are not propagated to the subnets.
Why it's wrong here
Route tables are associated with subnets; propagation is not relevant for VPC peering.
- ✗
The instances do not have ICMP traffic allowed.
Why it's wrong here
ICMP is not required for TCP/UDP communication.
- ✗
The VPC CIDR ranges overlap.
Why it's wrong here
The CIDRs 10.0.0.0/16 and 172.16.0.0/16 do not overlap.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ANS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the ANS-C01 exam.