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Home Forums AWS AWS Certified Advanced Networking – Specialty VPC CIDR Error in Answers

  • VPC CIDR Error in Answers

  • milo

    Member
    February 22, 2022 at 1:52 am

    Hi Tutorials Dojo Team!

    I believe you have an error in an answer to one of your questions in the AWS Advanced Networking Specialty practice test “Timed Mode Set 1.”

    The question reads:

    A company is setting up a central Virtual Private Cloud named VPC A with one subnet and two VPC peering connections. The first connection is between VPC A and VPC B ( pcx-aaaabbbb ) and the second is betweeen VPC A and VPC C ( pcx-aaaacccc ). VPC B and VPC C both have one EC2 instance each with the same 10.0.0.10 IP address as shown in the diagram below: 

    The CIDR Blocks of each VPCs are as follows:

    VPC A - 172.16.0.0/16
    VPC B - 10.0.0.0/16
    VPC C - 10.0.0.0/16

    VPC A should have two EC2 instances (E3 and E4) with custom private addresses 172.16.0.10 and 172.16.0.22 respectively. The E3 server in VPC A must be able to exclusively connect to E1 in VPC B while the E4 server in VPC A must be able to exclusively connect to the E2 in VPC C. Connections from the E3 server to E2 and from E4 server to E1 must be blocked.

    How can the Network Administrator properly setup this architecture?

    In 3 of the possible answers, the CIDR is written incorrectly based on the desired IP addresses for the two instances in VPC A.

    172.16.1.0/28 and 172.16.1.16/28 are supposed to be part of the “correct” answer but neither returns the desired instance IPs of 172.16.0.10 and 172.16.0.22.

    • The host range for 172.16.1.0/28 = 172.16.1.1 thru 172.16.1.14 (the desired IP 172.16.0.10 does not fall in this range)
    • The host range for 172.16.1.16/28 = 172.16.1.17 thru 172.16.1.31 (the desired IP 172.16.0.22 does not fall in this range)

    The correct ranges for this answer should be:

    • 172.16.0.0/28 (the desired IP 172.16.0.10 falls into this range)
    • 172.16.0.16/28 (the desired IP 172.16.0.22 falls into this range)

    I love your practice tests, just wanted to let you know that the CIDR addresses for the correct answer are wrong and you might want to fix that. 🙂 Please let me know if you have any questions.

    Thanks and keep up the great material!

  • Tutorials-Dojo

    Administrator
    March 29, 2022 at 10:45 pm

    Hi Milo,

    Thank you so much for bringing this to our attention. You are right, the IP addresses are jumbled up. We will fix the values and the change will be reflected to our practice tests soon.

    Cheers,

    Jon Bonso

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