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Question 748 of 1,705

Network Design →easyMultiple ChoiceObjective-mapped

ANS-C01 Network Design Practice Question

This ANS-C01 practice question tests your understanding of network design. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 has a VPC peering connection between VPC A (10.0.0.0/16) and VPC B (10.1.0.0/16). They have added routes in both route tables. However, instances in VPC A cannot ping instances in VPC B. The security groups and network ACLs allow ICMP. What is the most likely cause?

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.

A
The security groups in VPC B do not allow inbound ICMP from VPC A CIDR
Why wrong: The question states security groups allow ICMP, so this is not the cause.
B
The route tables in VPC A do not have a route to VPC B CIDR pointing to the peering connection
Without a specific route to the peered VPC CIDR, traffic will not be sent over the peering connection.
C
The VPC peering connection is not in the 'active' state
Why wrong: If the peering connection is not active, the route tables would show the target as 'blackhole', but the question implies routes are added, so likely active.
D
The instances are in different Availability Zones
Why wrong: Availability Zones do not affect VPC peering; traffic between VPCs is independent of AZ.

Full breakdown with real-world context →

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 route tables in VPC A do not have a route to VPC B CIDR pointing to the peering connection

The question states that routes have been added in both route tables, but the most likely cause is that the route in VPC A's route table does not point to the VPC peering connection as the target. Without a specific route for VPC B's CIDR (10.1.0.0/16) with the peering connection ID as the target, traffic from VPC A to VPC B will not be forwarded over the peering link, even if security groups and NACLs permit ICMP.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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 security groups in VPC B do not allow inbound ICMP from VPC A CIDR
Why it's wrong here
The question states security groups allow ICMP, so this is not the cause.
✓
The route tables in VPC A do not have a route to VPC B CIDR pointing to the peering connection
Why this is correct
Without a specific route to the peered VPC CIDR, traffic will not be sent over the peering connection.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The VPC peering connection is not in the 'active' state
Why it's wrong here
If the peering connection is not active, the route tables would show the target as 'blackhole', but the question implies routes are added, so likely active.
✗
The instances are in different Availability Zones
Why it's wrong here
Availability Zones do not affect VPC peering; traffic between VPCs is independent of AZ.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often assume that simply creating a VPC peering connection and adding routes generically is sufficient, but they overlook the requirement that the route must explicitly point to the peering connection ID as the target, not just any route to the peer CIDR.

Trap categories for this question

Command / output trap
If the peering connection is not active, the route tables would show the target as 'blackhole', but the question implies routes are added, so likely active.

Detailed technical explanation

How to think about this question

VPC peering relies on explicit routes in each VPC's route table pointing to the peering connection ID as the target for the peer's CIDR. Without this route, the VPC router has no path to forward traffic to the peer VPC, even if the peering is active and security rules permit traffic. A common real-world scenario is when a peering connection is created but the route tables are not updated, leading to connectivity failures that are often misdiagnosed as security group issues.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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.

Visual reference

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this ANS-C01 question test?

Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The route tables in VPC A do not have a route to VPC B CIDR pointing to the peering connection — The question states that routes have been added in both route tables, but the most likely cause is that the route in VPC A's route table does not point to the VPC peering connection as the target. Without a specific route for VPC B's CIDR (10.1.0.0/16) with the peering connection ID as the target, traffic from VPC A to VPC B will not be forwarded over the peering link, even if security groups and NACLs permit ICMP.

What should I do if I get this ANS-C01 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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?

Read the scenario before looking for a memorised answer.

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