- A
Security group rules on the VPC resources to allow inbound traffic from on-premises
Security groups control traffic flow.
- B
On-premises firewall rules to allow IPsec traffic
Firewall must allow IPsec (UDP 500, 4500, ESP).
- C
Network ACLs for the subnet to allow return traffic
Why wrong: NACLs are stateless; if outbound is allowed, return is automatic.
- D
Internet Gateway attachment to the VPC
Why wrong: Internet Gateway is for internet traffic, not VPN.
- E
VPC route table for a route to the on-premises CIDR pointing to the virtual private gateway
Without this route, traffic cannot reach the VPN.
Question 1,073 of 1,705
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 network engineer is configuring a site-to-site VPN connection between an on-premises network and AWS. The VPN tunnel is established, but traffic is not flowing. Which THREE components should the engineer check?
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
✓
Security group rules on the VPC resources to allow inbound traffic from on-premises
Options A, B, and E are correct. Security group rules must allow inbound traffic from the on-premises network (A). On-premises firewall rules must permit IPsec traffic (B). The VPC route table must have a route to the on-premises CIDR via the virtual private gateway (E). Option C is incorrect because Network ACLs are stateless and not the primary issue; they automatically allow return traffic if outbound is allowed. Option D is incorrect because an Internet Gateway is not used for VPN traffic; VPN traffic goes through the virtual private gateway.
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.
- ✓
Security group rules on the VPC resources to allow inbound traffic from on-premises
Why this is correct
Security groups control traffic flow.
Related concept
CIDR notation defines the prefix length.
- ✓
On-premises firewall rules to allow IPsec traffic
- ✗
Network ACLs for the subnet to allow return traffic
Why it's wrong here
NACLs are stateless; if outbound is allowed, return is automatic.
- ✗
Internet Gateway attachment to the VPC
- ✓
VPC route table for a route to the on-premises CIDR pointing to the virtual private gateway
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
Quick reference
VPN Protocol Comparison
| Protocol | Port | Encryption | Authentication | Use Case |
|---|---|---|---|---|
| IKEv2 / IPsec | UDP 500 / 4500 | AES-256 | Certificates / PSK | Site-to-site & remote access |
| SSL / TLS VPN | TCP 443 | TLS 1.3 | Certificates / MFA | Clientless remote access |
| L2TP / IPsec | UDP 1701 | AES (IPsec) | PSK / Certificates | Legacy remote access |
| WireGuard | UDP 51820 | ChaCha20 | Public keys | Modern high-performance VPN |
| PPTP | TCP 1723 | MPPE (weak) | MS-CHAPv2 | Legacy — avoid in production |
PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.
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: Security group rules on the VPC resources to allow inbound traffic from on-premises — Options A, B, and E are correct. Security group rules must allow inbound traffic from the on-premises network (A). On-premises firewall rules must permit IPsec traffic (B). The VPC route table must have a route to the on-premises CIDR via the virtual private gateway (E). Option C is incorrect because Network ACLs are stateless and not the primary issue; they automatically allow return traffic if outbound is allowed. Option D is incorrect because an Internet Gateway is not used for VPN traffic; VPN traffic goes through the virtual private gateway.
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
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