ANS-C01 Network Implementation Practice Question
A network engineer is troubleshooting connectivity issues between two VPCs connected via a VPC peering connection. The VPCs are in different AWS accounts and regions. The engineer can ping the private IP of an instance in the peered VPC from one side, but not from the other. What is the most likely cause?
⚠ Common exam trap
The ANS-C01 exam often tests the misconception that security groups or network ACLs are the primary cause of one-way connectivity issues, but the real trap is that route table misconfiguration is the most common reason for asymmetric traffic flow in VPC peering scenarios.
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
✓
Route tables in one VPC do not have a route to the peered VPC CIDR
The most likely cause is that the route tables in one VPC lack a route pointing to the peered VPC's CIDR block. For a VPC peering connection to function bidirectionally, each VPC must have a route in its route table that directs traffic destined for the other VPC's CIDR to the peering connection (pcx-*). Without this route, packets from the source VPC to the peered VPC will be dropped, even if the peering connection itself is active and the security groups allow traffic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Route tables in one VPC do not have a route to the peered VPC CIDR
Why this is correct
A missing route in one VPC prevents return traffic, causing one-way connectivity.
- ✗
The security group in the peered VPC is blocking ICMP traffic
Why it's wrong here
Security group rules are stateful and would block traffic both ways.
- ✗
The VPC CIDR blocks overlap
Why it's wrong here
Overlapping CIDRs would prevent peering altogether.
- ✗
The VPC peering connection is in a 'pending-acceptance' state
Why it's wrong here
If pending, neither side would work.
Visual reference
Go deeper
Related to this question
About these practice questions
This ANS-C01 question is part of Courseiva's 1,621-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
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.