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Network Management and Operations →mediumMultiple ChoiceObjective-mapped

ANS-C01 Network Management and Operations Practice Question

This ANS-C01 practice question tests your understanding of network management and operations. 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 uses AWS Direct Connect to connect its on-premises data center to a VPC. The connection uses a private virtual interface (VIF) and BGP. The network team recently added a new CIDR block (10.0.3.0/24) to the VPC. They updated the VPC's route table to include a route to the on-premises network. However, the on-premises network cannot reach resources in the new subnet. The BGP session is up, and the Direct Connect gateway is configured. What should the network team do to resolve the issue?

A
Add a static route in the on-premises router pointing to the Direct Connect interface.
Why wrong: Static route would work but does not address the BGP advertisement. The issue is the missing prefix in allowed prefixes.
B
Set up a new VPN connection as a backup and route traffic over VPN.
Why wrong: Not necessary; the Direct Connect connection is functional, just missing prefix advertisement.
C
Add the new CIDR block (10.0.3.0/24) to the Direct Connect gateway's allowed prefixes.
This allows the Direct Connect gateway to advertise the new prefix to the on-premises network via BGP.
D
Create a new private VIF for the new CIDR block.
Why wrong: A single private VIF can handle multiple CIDRs; no need for a new VIF.

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

✓

Add the new CIDR block (10.0.3.0/24) to the Direct Connect gateway's allowed prefixes.

When a new CIDR block is added to an existing VPC connected via Direct Connect, the Direct Connect gateway must be updated to include the new prefix in its allowed prefixes list. By default, the Direct Connect gateway only advertises prefixes that are explicitly allowed. The on-premises network cannot reach the new subnet because the gateway is not advertising the 10.0.3.0/24 route via BGP. Option C is correct: add the new CIDR to the Direct Connect gateway's allowed prefixes. Option A is incorrect because adding a static route on the on-premises router does not affect BGP advertisements from the AWS side; the gateway must advertise the route. Option B is unnecessary and adds complexity; the issue is with prefix propagation, not with connectivity. Option D is incorrect because a new private VIF is not needed; the existing VIF can handle multiple prefixes if allowed.

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.

✗
Add a static route in the on-premises router pointing to the Direct Connect interface.
Why it's wrong here
Static route would work but does not address the BGP advertisement. The issue is the missing prefix in allowed prefixes.
✗
Set up a new VPN connection as a backup and route traffic over VPN.
Why it's wrong here
Not necessary; the Direct Connect connection is functional, just missing prefix advertisement.
✓
Add the new CIDR block (10.0.3.0/24) to the Direct Connect gateway's allowed prefixes.
Why this is correct
This allows the Direct Connect gateway to advertise the new prefix to the on-premises network via BGP.
Related concept
CIDR notation defines the prefix length.
✗
Create a new private VIF for the new CIDR block.
Why it's wrong here
A single private VIF can handle multiple CIDRs; no need for a new VIF.

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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.

Visual reference

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 ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this ANS-C01 question test?

Network Management and Operations — This question tests Network Management and Operations — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: Add the new CIDR block (10.0.3.0/24) to the Direct Connect gateway's allowed prefixes. — When a new CIDR block is added to an existing VPC connected via Direct Connect, the Direct Connect gateway must be updated to include the new prefix in its allowed prefixes list. By default, the Direct Connect gateway only advertises prefixes that are explicitly allowed. The on-premises network cannot reach the new subnet because the gateway is not advertising the 10.0.3.0/24 route via BGP. Option C is correct: add the new CIDR to the Direct Connect gateway's allowed prefixes. Option A is incorrect because adding a static route on the on-premises router does not affect BGP advertisements from the AWS side; the gateway must advertise the route. Option B is unnecessary and adds complexity; the issue is with prefix propagation, not with connectivity. Option D is incorrect because a new private VIF is not needed; the existing VIF can handle multiple prefixes if allowed.

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

What is the key concept behind this question?

CIDR notation defines the prefix length.

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