ANS-C01 Network Design — 10 Questions

Question 1

A company is migrating its on-premises data center to AWS. The network team needs to establish connectivity between the on-premises network and multiple VPCs in a single AWS Region. The company has a Direct Connect connection and wants to minimize latency and cost while maximizing bandwidth utilization. Which solution meets these requirements?

Accepted Answer

Use a Direct Connect gateway and associate it with the VPCs.. A Direct Connect gateway allows a single Direct Connect connection to connect to multiple VPCs in the same or different AWS Regions, minimizing latency by using a private, dedicated network path and reducing cost by eliminating the need for separate virtual interfaces or VPN tunnels per VPC. It also maximizes bandwidth utilization by aggregating traffic from multiple VPCs over the same Direct Connect link.

Answer

Provision a separate Direct Connect virtual interface for each VPC.

Answer

Create a VPN connection over the Direct Connect link to each VPC.

Answer

Use VPC peering between the on-premises network and each VPC.

Question 2

A global e-commerce company uses a hub-and-spoke network topology with a transit VPC in us-east-1. Each spoke VPC has an AWS Site-to-Site VPN connection to its respective on-premises office. Users report intermittent connectivity issues when accessing a web application hosted in a spoke VPC in eu-west-1 from an on-premises office in ap-southeast-1. The network engineer checks the VPN connection and finds it is up. Which design change would MOST likely resolve the issue?

Accepted Answer

Enable jumbo frames on the transit VPC's EC2-based virtual appliances.. The issue is intermittent connectivity between an on-premises office in ap-southeast-1 and a spoke VPC in eu-west-1, traversing a transit VPC in us-east-1. The VPN is up, so the problem is likely packet fragmentation or MTU mismatch across the long-haul path. Enabling jumbo frames on the transit VPC's EC2-based virtual appliances (e.g., firewall or router instances) increases the maximum transmission unit, reducing fragmentation and improving performance for large packets, which is a common cause of intermittent issues in hub-and-spoke topologies.

Answer

Change the VPN connection from static to dynamic routing.

Answer

Enable BGP route propagation on the transit VPC's route tables.

Answer

Deploy a new transit VPC in eu-west-1.

Question 3

A company is designing a network for a three-tier web application in a single VPC. The web tier must be accessible from the internet, but the application and database tiers must not have direct internet access. The application servers need to make outbound calls to a third-party API. Which architecture meets these requirements?

Accepted Answer

Web servers in public subnets with an Application Load Balancer, application servers in private subnets with a NAT gateway, and database servers in private subnets.. Option C is correct because it places web servers in public subnets with an Application Load Balancer for inbound internet traffic, while application and database servers reside in private subnets without direct internet access. A NAT gateway in a public subnet enables the application servers to initiate outbound connections to a third-party API, with return traffic automatically routed back, meeting the requirement for outbound-only internet access.

Answer

Web servers in public subnets, application and database servers in private subnets with an internet gateway for outbound traffic.

Answer

All servers in public subnets with security groups restricting access.

Answer

All servers in private subnets and a VPN connection to the internet.

Question 4

A company has a Direct Connect connection with two private virtual interfaces (VIFs) to two different VPCs in the same AWS Region. The company wants to use AWS Transit Gateway to simplify connectivity between these VPCs and their on-premises network. Which steps are required to integrate the existing Direct Connect connection with Transit Gateway?

Accepted Answer

Create a Direct Connect gateway, associate the existing VIFs, and attach the Direct Connect gateway to the Transit Gateway.. Option D is correct because AWS Direct Connect private VIFs cannot be attached directly to a Transit Gateway. Instead, you must create a Direct Connect Gateway, associate the existing private VIFs with it, and then attach the Direct Connect Gateway to the Transit Gateway. This architecture allows the Transit Gateway to route traffic between the on-premises network (via the Direct Connect connection) and the attached VPCs, while also enabling inter-VPC routing through the Transit Gateway.

Answer

Set up a VPN connection over the Direct Connect link and attach the VPN to the Transit Gateway.

Answer

Attach the existing private VIFs directly to the Transit Gateway.

Answer

Create a new private VIF on the Direct Connect connection and attach it to the Transit Gateway.

Question 5

A company is designing a multi-region architecture with VPCs in us-east-1 and eu-west-1. The company needs low-latency connectivity between the VPCs and wants to avoid traffic over the public internet. The VPCs have overlapping CIDR blocks (10.0.0.0/16). Which solution should the network engineer recommend?

Accepted Answer

Set up an AWS Transit Gateway in each region and connect them via a VPN attachment.. Option A is correct because AWS Transit Gateway supports inter-region peering attachments that use the AWS global network backbone, providing low-latency, private connectivity between VPCs in different regions. Even when VPCs have overlapping CIDR blocks, Transit Gateway can handle this through route table isolation and network segmentation (e.g., using separate route tables for each VPC attachment), which VPC peering cannot do. VPN attachments between Transit Gateways in each region establish encrypted tunnels over the AWS backbone, avoiding the public internet.

Answer

Use a Direct Connect connection between the regions.

Answer

Use VPC peering between the two VPCs.

Answer

Place all resources in a single VPC with multiple Availability Zones.

Question 6

A company is designing a hybrid network using AWS Transit Gateway. The company has three VPCs (VPC-A, VPC-B, VPC-C) all attached to the same Transit Gateway. The on-premises network connects to the Transit Gateway via a Direct Connect gateway. The company needs to ensure that VPC-C can communicate with the on-premises network but not with VPC-A or VPC-B. Which TWO actions should the network engineer take?

Accepted Answer

Associate the VPC-C route table with the Direct Connect gateway attachment.. Option B is correct because associating the VPC-C route table with the Direct Connect gateway attachment allows VPC-C to exchange routes with the on-premises network via the Transit Gateway, enabling communication. Option D is correct because creating a separate Transit Gateway route table for VPC-C and not propagating VPC-A and VPC-B routes ensures that VPC-C has no routes to those VPCs, effectively isolating it from them at the network layer.

Answer

Use security groups on VPC-C to deny traffic from VPC-A and VPC-B.

Answer

Establish VPC peering connections between VPC-C and VPC-A, and VPC-C and VPC-B.

Answer

Apply a network ACL on VPC-C subnets to block traffic from VPC-A and VPC-B.

Question 7

A company is deploying a new application in a VPC. The application consists of EC2 instances in an Auto Scaling group behind an Application Load Balancer (ALB). The ALB must only receive traffic from the company's on-premises network via an AWS Site-to-Site VPN. Which THREE steps should the network engineer take to meet this requirement?

Accepted Answer

Place the ALB in a public subnet.. Option B is correct because an Application Load Balancer (ALB) must be placed in a public subnet to be reachable from an on-premises network via an AWS Site-to-Site VPN. The VPN connection terminates on a virtual private gateway or transit gateway, which routes traffic to the VPC, but the ALB itself needs a public subnet with a route to the internet gateway (or virtual private gateway) to accept inbound traffic from the VPN. Without a public subnet, the ALB cannot receive traffic from outside the VPC, including VPN traffic.

Answer

Place the ALB in a private subnet and use a Transit Gateway.

Answer

Create a NAT gateway in the public subnet for outbound traffic.

Question 8

A network engineer has configured an AWS Site-to-Site VPN connection between a VPC and an on-premises network. The engineer checks the VPN status and sees the output above. What is the MOST likely cause of Tunnel2 being down?

Accepted Answer

The IPsec encryption or integrity algorithms do not match between the AWS VPN endpoint and the on-premises device.. Tunnel2 is down while Tunnel1 is up, indicating a per-tunnel configuration mismatch. The most common cause is a mismatch in IPsec security parameters (encryption, integrity, or DH group) between the AWS VPN endpoint and the on-premises device for that specific tunnel. AWS uses separate pre-shared keys and IPsec settings per tunnel, so a mismatch in algorithms would affect only the misconfigured tunnel.

Answer

The BGP ASN on the on-premises device is misconfigured.

Answer

The route tables in the VPC do not have a route to the on-premises network.

Answer

The IKE pre-shared key used for Tunnel2 is incorrect.

Question 9

A network engineer is setting up a cross-account Route 53 Resolver rule association. The engineer creates the above resource-based policy on a resolver rule in account 111111111111. The engineer then tries to associate the rule from account 222222222222 but receives an access denied error. What is the MOST likely reason for the failure?

Accepted Answer

The policy's Principal is set to account 111111111111 instead of account 222222222222.. The resource-based policy on the Route 53 Resolver rule must specify the consuming account (222222222222) as the Principal to authorize cross-account association. Since the policy incorrectly sets the Principal to the owning account (111111111111), the request from account 222222222222 lacks the required permissions, resulting in an access denied error.

Answer

The policy does not allow the 'route53resolver:AssociateResolverRule' action.

Answer

The policy does not include the 'route53resolver:DisassociateResolverRule' action.

Answer

The resolver rule is not shared with account 222222222222.

Question 10

A company has a VPC with public and private subnets in two Availability Zones. An Application Load Balancer in the public subnets distributes traffic to EC2 instances in the private subnets. The security group for the EC2 instances allows inbound traffic from the ALB security group. Users report intermittent timeouts. What is the most likely cause?

Accepted Answer

The security group for the ALB does not allow inbound traffic from the internet.. The most likely cause is that the ALB's security group does not allow inbound traffic from the internet (0.0.0.0/0) on the listener port (e.g., 80 or 443). Without this rule, the ALB will reject incoming client requests, causing intermittent timeouts as users attempt to connect. The ALB must have an inbound rule permitting traffic from the internet to receive and forward requests to the targets.

Answer

The ALB is not associated with an internet gateway.

Answer

The network ACL for the private subnets is blocking inbound traffic from the ALB subnets.

Answer

Cross-zone load balancing is disabled on the ALB.