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Exam AWS-SysOps topic 1 question 91 discussion

Exam question from Amazon's AWS-SysOps
Question #: 91
Topic #: 1
[All AWS-SysOps Questions]

A user has created a VPC with CIDR 20.0.0.0/24. The user has created a public subnet with CIDR 20.0.0.0/25. The user is trying to create the private subnet with
CIDR 20.0.0.128/25. Which of the below mentioned statements is true in this scenario?

  • A. It will not allow the user to create the private subnet due to a CIDR overlap
  • B. It will allow the user to create a private subnet with CIDR as 20.0.0.128/25
  • C. This statement is wrong as AWS does not allow CIDR 20.0.0.0/25
  • D. It will not allow the user to create a private subnet due to a wrong CIDR range
Show Suggested Answer Hide Answer
Suggested Answer: B 🗳️
When the user creates a subnet in VPC, he specifies the CIDR block for the subnet. The CIDR block of a subnet can be the same as the CIDR block for the VPC
(for a single subnet in the VPC., or a subset (to enable multiple subnets. If the user creates more than one subnet in a VPC, the CIDR blocks of the subnets must not overlap. Thus, in this case the user has created a VPC with the CIDR block 20.0.0.0/24, which supports 256 IP addresses (20.0.0.0 to 20.0.0.255. The user can break this CIDR block into two subnets, each supporting 128 IP addresses. One subnet uses the CIDR block 20.0.0.0/25 (for addresses 20.0.0.0 - 20.0.0.127. and the other uses the CIDR block 20.0.0.128/25 (for addresses 20.0.0.128 - 20.0.0.255.

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karmaah
Highly Voted 1 year, 6 months ago
CIDR Range :20.0.0.0/24 => Total 20.0.0.255 Public Subet IP Range : 20.0.0.0/25 => IPs starts from 20.0.0.0 to 20.0.0.127 Private Subnet IP Range : 20.0.0.128/25 => IPs starts from 20.0.0.128 to 20.0.0.255
upvoted 12 times
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Finger41
Most Recent 9 months, 3 weeks ago
Selected Answer: B
Tested it - B
upvoted 1 times
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nafazoline
1 year, 6 months ago
I tested it. It's OK. correct answer is B although it is not a private ip (Those are suposed to be only 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16)
upvoted 1 times
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TroyMcLure
1 year, 6 months ago
Correct Answer: B
upvoted 1 times
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awscertified
1 year, 6 months ago
B. It will allow the user to create a private subnet with CIDR as 20.0.0.128/25
upvoted 1 times
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newtoaws
1 year, 6 months ago
Answer should be D, 20.0.0.0 cannot be used for private
upvoted 2 times
badrobot
1 year, 6 months ago
https://docs.aws.amazon.com/vpc/latest/userguide/vpc-ip-addressing.html We refer to private IP addresses as the IP addresses that are within the IPv4 CIDR range of the VPC. Most VPC IP address ranges fall within the private (non-publicly routable) IP address ranges specified in RFC 1918; however, you can use publicly routable CIDR blocks for your VPC. Regardless of the IP address range of your VPC, we do not support direct access to the Internet from your VPC's CIDR block, including a publicly-routable CIDR block. You must set up Internet access through a gateway; for example, an Internet gateway, virtual private gateway, a AWS Site-to-Site VPN connection, or AWS Direct Connect.
upvoted 1 times
badrobot
1 year, 6 months ago
Answer B
upvoted 6 times
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