- A
The on-premises router is not advertising the on-premises CIDR prefix via BGP.
If BGP does not advertise the prefix, the Direct Connect gateway will not propagate the route to the VPC.
- B
The AWS Direct Connect connection is not associated with the correct Direct Connect gateway.
Why wrong: If BGP is established, the association is correct.
- C
The virtual interface is in a 'down' state.
Why wrong: The scenario says the VIF is up.
- D
The VPC route table does not have a route to the on-premises CIDR pointing to the Direct Connect virtual interface.
Missing route prevents traffic from VPC to on-premises.
- E
The security group attached to the EC2 instance blocks inbound traffic from on-premises.
Why wrong: Security groups are stateful; if outbound is allowed, return traffic is allowed. However, initial traffic could be blocked, but this is less likely than routing issues.
Quick Answer
The answer is a missing route in the VPC route table and an incorrect prefix advertisement from the on-premises router. Even when BGP is established and the virtual interface is up, traffic cannot flow unless both sides have valid routing entries; the VPC route table must contain a route pointing to the Direct Connect virtual interface for the on-premises CIDR, and the on-premises router must advertise the correct prefix to the VPC. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this scenario tests your understanding that BGP session state is independent of actual data-plane forwarding—a common trap is assuming a “BGP established” status guarantees traffic flow, when in fact missing or misconfigured routes are the silent culprit. Remember the memory tip: “BGP up does not mean traffic flows—check the route tables first.”
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 is troubleshooting connectivity issues between an on-premises network and a VPC connected via AWS Direct Connect. The network team has verified that the virtual interface (VIF) is up and BGP is established. However, traffic is not flowing. Which two configuration issues could cause this problem? (Choose TWO.)
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 on-premises router is not advertising the on-premises CIDR prefix via BGP.
Correct routes on both sides are needed. If the VPC route table does not have a route to the on-premises CIDR via the Direct Connect VIF, traffic won't flow. Similarly, if the on-premises router does not advertise the correct prefix, or if the VPC's route table lacks a route, connectivity fails. Security group rules might block, but they are not the most likely if BGP is up. The VIF state is up, so that's not the issue.
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 on-premises router is not advertising the on-premises CIDR prefix via BGP.
- ✗
The AWS Direct Connect connection is not associated with the correct Direct Connect gateway.
Why it's wrong here
If BGP is established, the association is correct.
- ✗
The virtual interface is in a 'down' state.
Why it's wrong here
The scenario says the VIF is up.
- ✓
The VPC route table does not have a route to the on-premises CIDR pointing to the Direct Connect virtual interface.
Why this is correct
Missing route prevents traffic from VPC to on-premises.
Related concept
CIDR notation defines the prefix length.
- ✗
The security group attached to the EC2 instance blocks inbound traffic from on-premises.
Why it's wrong here
Security groups are stateful; if outbound is allowed, return traffic is allowed. However, initial traffic could be blocked, but this is less likely than routing issues.
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.
Trap categories for this question
Scenario analysis trap
The scenario says the VIF is up.
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.
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: The on-premises router is not advertising the on-premises CIDR prefix via BGP. — Correct routes on both sides are needed. If the VPC route table does not have a route to the on-premises CIDR via the Direct Connect VIF, traffic won't flow. Similarly, if the on-premises router does not advertise the correct prefix, or if the VPC's route table lacks a route, connectivity fails. Security group rules might block, but they are not the most likely if BGP is up. The VIF state is up, so that's not the issue.
What should I do if I get this ANS-C01 question wrong?
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Last reviewed: Jun 20, 2026
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.
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