secondary CIDR block

[masterJ]

I have this question and I hope you can help me out. this question is inspired from the practice test. So I have a CIDR block of 10.0.0.0/16 and I need to associate a secondary CIDR blocks. Which CIDR block can I use (pick 2)? 34.17.0.0/16, 100.77.0.0/16, 172.16.0.0/16, and 192.168.0.0/16? I picked 172.16 and 192.168 but it said it is wrong. What are your thoughts? Thx

[JR-TutorialsDojo]

Hello masterJ,

Thank you for reaching out. Could you please provide the snippet of the question so we can assist you further?

Regards,
JR @ Tutorials Dojo

[massivenk]

6. Question

A large multinational organization has an existing VPC with a 10.0.0.0/16 primary CIDR block. All of the 65,531 usable IP addresses were already used. The Network Engineer has been assigned to associate new secondary CIDR blocks to scale out the VPC size.

Which of the following blocks can the Administrator associate to the existing VPC? (Select TWO.)

[JR-TutorialsDojo]

Hello masterJ,

As mentioned in the explanation, the reason your answer was marked incorrect is due to AWS VPC restrictions on mixing RFC 1918 ranges. While 172.16.0.0/16 and 192.168.0.0/16 are valid private IP ranges under RFC 1918, AWS does not allow you to associate secondary CIDR blocks from different RFC 1918 ranges when your primary CIDR block is already within one of them.

In this case, since the primary CIDR block is 10.0.0.0/16, you cannot use 172.16.0.0/16 or 192.168.0.0/16 as secondary blocks. Please refer to the attached image.

I hope this helps! Let us know if you need further assistance.

Regards,
JR @ Tutorials Dojo