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Exam AWS Certified Advanced Networking - Specialty ANS-C01 topic 1 question 231 discussion

Exam question from Amazon's AWS Certified Advanced Networking - Specialty ANS-C01
Question #: 231
Topic #: 1
[All AWS Certified Advanced Networking - Specialty ANS-C01 Questions]

A company hosts a highly available, scalable, and resilient application on Amazon EC2 instances that are part of an Auto Scaling group. A network engineer is planning to integrate IPv6 support with the application deployment in phases. The first phase is to enable IPv6 service consumption on the public Network Load Balancers (NLBs) that are deployed across the infrastructure. The target groups for the NLBS are configured as the Auto Scaling groups of the EC2 instances that host the application. The NLBs are configured for dual-stack operation.

During the testing of the first phase, the IPv6 application queries are not reaching the backend servers.

What is the cause of this issue?

  • A. The subnets where the EC2 instances are deployed do not have IPv6 addresses configured.
  • B. The route tables for the NLB subnets do not have IPV6 routing configured.
  • C. The route tables for the EC2 subnets do not have IPV6 routing configured.
  • D. The security groups that are associated with the NLBs do not allow IPv6 traffic.
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Suggested Answer: C 🗳️
by djangoGroup at Jan. 9, 2025, 7:08 a.m.
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ashk123456
2 weeks, 5 days ago
Selected Answer: A
For IPv6 traffic to flow from the NLB to the backend EC2 instances, the EC2 instances need to have IPv6 addresses assigned. Since the first phase was only to enable IPv6 on the NLBs, the backend EC2 instances likely weren't prepared to handle IPv6 traffic. Without IPv6 addresses configured in the EC2 subnets, the NLB cannot forward IPv6 traffic to the targets.
upvoted 1 times
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c1193d4
1 month, 3 weeks ago
Selected Answer: B
See https://docs.aws.amazon.com/whitepapers/latest/ipv6-on-aws/scaling-the-dual-stack-network-design-in-aws.html NLB does the IPv6 to IPv4 conversion during this first phase so that no IPv6 configuration is necessary in the EC2 subnet
upvoted 1 times
c1193d4
1 month, 3 weeks ago
D would probably be a good choice also ... I suppose that NLB dual-stack activation is no possible if the subnets have no IPv6 address
upvoted 1 times
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djangoGroup
3 months, 1 week ago
Selected Answer: A
The EC2 subnets (where the Auto Scaling group instances run) do not have IPv6 addresses configured. Therefore, even though the Network Load Balancer (NLB) is operating in dual-stack mode and can accept IPv6 connections, it cannot forward IPv6 traffic to instances that do not themselves have IPv6 addresses in the same subnet.
upvoted 3 times
victian
1 month, 1 week ago
but i think the ip address should be allocated when the elb launch the instance？
upvoted 1 times
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