Which is the most likely reason for this issue?

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In: SAP-C01
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Doug has created a VPC with CIDR 10.201.0.0/16 in his AWS account.In this VPC he has created a public subnet with CIDR block 10.201.31.0/24.While launching a new EC2 from the console, he is not able to assign the private IP address 10.201.31.6 to this instance.

Which is the most likely reason for this issue?

Private address IP 10.201.31.6 is currently assigned to another interface

Private IP address 10.201.31.6 is reserved by Amazon for IP networking purposes.

Private IP address 10.201.31.6 is blocked via ACLs in Amazon infrastructure as a part of platform security.

Private IP address 10.201.31.6 is not part of the associated subnet’s IP address range.

Explanations:

The IP address 10.201.31.6 may already be assigned to another network interface, preventing its reuse.

AWS reserves certain IPs in each subnet, such as the first four and the last IP, but 10.201.31.6 is not among these reserved addresses.

AWS does not block specific IP addresses in subnets for security reasons; ACLs would not prevent assigning this IP.

10.201.31.6 is within the range of the 10.201.31.0/24 subnet, so it is part of the associated subnet’s IP range.

2026-03-21

2 Comments

  1. Edward
    Author

    I sort that the answer is:
    Private address IP 10.201.31.6 is currently assigned to another interface

  2. Ashley
    Author

    If I’m not mistaken, the answer is:
    Private address IP 10.201.31.6 is currently assigned to another interface

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