AWS Certified Advanced Networking - Specialty Exam: Troubleshooting EC2 Instances in Private Subnets

Possible Underlying Issue with Configured NAT Instances for Application Updates

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Question

You currently have EC2 Instances in a private subnets.

There are applications based on IPv6 which are hosted on these instances.

You have configured NAT instances in a public subnet to ensure that applications hosted on the instances in the private subnet can download the required updates.

But after configuring the instances , the applications are still not able to download the updates.

Which of the following could be the underlying issue.

Answers

A. The NAT instance should not be configured in the public subnet , it should be configured in the private subnet

B. The NAT instance is not configured with a private IP address.

C. NAT is not supported for IPv6 traffic

D. The NAT instance is not configured with a private DNS name.

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Explanations

Click on the arrows to vote for the correct answer

A. B. C. D.

Answer - C.

The AWS documentation mentions the following.

NAT is not supported for IPv6 traffic-use an egress-only Internet gateway instead.

For more information on NAT Instances, please visit the link:

http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/VPC_NAT_Instance.html

The issue is related to the configuration of the NAT instances for IPv6 traffic. NAT (Network Address Translation) is not supported for IPv6 traffic. Therefore, option C is the correct answer.

NAT is used to translate private IP addresses to public IP addresses, and vice versa, to allow instances in a private subnet to access resources on the internet or other resources outside of the VPC. However, with IPv6, each instance can have a globally unique IP address, and NAT is not needed.

To resolve the issue, you should consider the following:

Ensure that the applications on the instances are configured to use IPv6 addresses, and not IPv4 addresses.
Make sure that the instances have the appropriate security group rules to allow inbound and outbound traffic.
Check that the instances have access to the internet gateway or VPC endpoint for the relevant services.
Verify that the instances have the necessary updates installed to support IPv6 traffic.

In summary, NAT is not supported for IPv6 traffic, and therefore it cannot be used to enable instances in a private subnet to access resources on the internet or other resources outside of the VPC. To enable communication between instances in a private subnet and the internet or other resources, you need to configure the VPC with appropriate security group rules, routes, and access to the necessary gateways or endpoints.

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