← SOA-C02·Amazon Web Services

Question 479 of 1,546

Networking and Content Delivery →mediumMultiple ChoiceObjective-mapped

SOA-C02 Networking and Content Delivery Practice Question

This SOA-C02 practice question tests your understanding of networking and content delivery. 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 an internal Application Load Balancer (ALB) in a VPC. The ALB is used by an on-premises application via AWS Direct Connect. The on-premises application needs to resolve the ALB's DNS name. The VPC has Route 53 private hosted zone associated with the VPC. The on-premises DNS servers are configured to forward queries for the company's domain to the VPC's Route 53 inbound resolver endpoints. However, the on-premises application cannot resolve the ALB's DNS name. What is the likely cause?

A
The ALB's security group blocks inbound traffic from the on-premises CIDR.
Why wrong: This would affect connectivity, not DNS resolution.
B
The ALB is internal and does not have a public DNS name.
Why wrong: Even internal ALBs have a public DNS name that resolves to the private IPs from within the VPC.
C
The ALB's DNS name is not in the Route 53 private hosted zone.
The on-premises DNS forwards to the inbound resolver, which only answers for the private hosted zone domain. The ALB's DNS name is a public domain (e.g., internal-alb-123456.elb.amazonaws.com) and is not in the private zone, so the resolver cannot resolve it.
D
The Route 53 inbound resolver is not configured to forward queries to the public internet.
Why wrong: The inbound resolver can be configured to resolve public names by forwarding to a DNS resolver, but the issue is that the ALB's DNS name is not in the private zone.

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 ALB's DNS name is not in the Route 53 private hosted zone.

The ALB is internal, meaning it does not have a public IP address but it still has a public DNS name (e.g., internal-alb-123456789.elb.amazonaws.com) that resolves to its private IP addresses within the VPC. The Route 53 private hosted zone is associated with the VPC and contains DNS records only for the company's custom domain (e.g., example.com). The on-premises DNS servers forward queries for the company's domain to the Route 53 inbound resolver, but the ALB's DNS name is not within that domain, so the resolver cannot resolve it. Therefore, the on-premises application cannot resolve the ALB's DNS name because it is not listed in the private hosted zone. Options A, B, and D are incorrect: A involves security groups which affect traffic, not DNS; B incorrectly claims internal ALBs don't have a DNS name; D is irrelevant because the inbound resolver is specifically for the private hosted zone domain, not for public DNS resolution.

Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

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 ALB's security group blocks inbound traffic from the on-premises CIDR.
Why it's wrong here
This would affect connectivity, not DNS resolution.
✗
The ALB is internal and does not have a public DNS name.
Why it's wrong here
Even internal ALBs have a public DNS name that resolves to the private IPs from within the VPC.
✓
The ALB's DNS name is not in the Route 53 private hosted zone.
Why this is correct
The on-premises DNS forwards to the inbound resolver, which only answers for the private hosted zone domain. The ALB's DNS name is a public domain (e.g., internal-alb-123456.elb.amazonaws.com) and is not in the private zone, so the resolver cannot resolve it.
Related concept
CIDR notation defines the prefix length.
✗
The Route 53 inbound resolver is not configured to forward queries to the public internet.
Why it's wrong here
The inbound resolver can be configured to resolve public names by forwarding to a DNS resolver, but the issue is that the ALB's DNS name is not in the private zone.

Common exam traps

Common exam trap: usable hosts are not the same as total addresses

Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.

Detailed technical explanation

How to think about this question

Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.

KKey Concepts to Remember

CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.

TExam Day Tips

Write the block size before choosing the subnet.
Check whether the question asks for hosts, subnets or a specific address range.
Do not confuse /24, /25, /26 and /27 host counts.

Key takeaway

Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

Real-world example

How this comes up in practice

A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.

Visual reference

Quick reference

Common DNS Record Types

Record	Purpose	Example
A	IPv4 address mapping	example.com → 93.184.216.34
AAAA	IPv6 address mapping	example.com → 2606:2800::1
CNAME	Alias to another hostname	www → example.com
MX	Mail server for domain	example.com → mail.example.com (priority 10)
TXT	Text data (SPF, DKIM, verification)	v=spf1 include:_spf.example.com ~all
NS	Authoritative name servers	example.com NS ns1.example.com
PTR	Reverse DNS (IP → hostname)	34.216.184.93.in-addr.arpa → example.com
SOA	Zone authority record	Primary NS, admin email, serial, TTL defaults

What to study next

Got this wrong? Here's your next step.

Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SOA-C02 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this SOA-C02 question test?

Networking and Content Delivery — This question tests Networking and Content Delivery — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: The ALB's DNS name is not in the Route 53 private hosted zone. — The ALB is internal, meaning it does not have a public IP address but it still has a public DNS name (e.g., internal-alb-123456789.elb.amazonaws.com) that resolves to its private IP addresses within the VPC. The Route 53 private hosted zone is associated with the VPC and contains DNS records only for the company's custom domain (e.g., example.com). The on-premises DNS servers forward queries for the company's domain to the Route 53 inbound resolver, but the ALB's DNS name is not within that domain, so the resolver cannot resolve it. Therefore, the on-premises application cannot resolve the ALB's DNS name because it is not listed in the private hosted zone. Options A, B, and D are incorrect: A involves security groups which affect traffic, not DNS; B incorrectly claims internal ALBs don't have a DNS name; D is irrelevant because the inbound resolver is specifically for the private hosted zone domain, not for public DNS resolution.

What should I do if I get this SOA-C02 question wrong?

What is the key concept behind this question?

CIDR notation defines the prefix length.

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