Public IP Addressing in AWS

Answer - D.

The AWS documentation mentions the following on public IP addressing.

A public IP address is assigned from Amazon's pool of public IP addresses; it's not associated with your account.

When a public IP address is disassociated from your instance, it's released back into the pool, and is no longer available for you to use.

You cannot manually associate or disassociate a public IP address.

For more information on IP addressing please refer to the below URL:

All of the options listed are true except for one. Therefore, the answer is option B, "When an IP is disassociated from the instance, it is added back to the pool." This is an incorrect statement as disassociated public IPs are not immediately added back to the pool.

Here is a detailed explanation of each option:

A. A public IP address is assigned from Amazon's pool of public IP addresses: Whenever a new instance is launched in AWS, a public IP address is assigned from Amazon's pool of public IP addresses. The public IP address is a unique address that is accessible from the internet. The public IP address can be associated with the instance when it is launched, or it can be assigned later.

B. When an IP is disassociated from the instance, it is added back to the pool: This is an incorrect statement. When a public IP address is disassociated from an instance, it is not immediately added back to the pool. Instead, the IP address is held for a brief period of time, and during this time, it can be associated with another instance in the same AWS account. This is to ensure that the same IP address is not reused too quickly and that any cached DNS entries for the previous instance have time to expire.

C. The Public IP allows the instance to be reachable from the internet: This is true. A public IP address allows the instance to be reached from the internet. When an instance has a public IP address, it can communicate with other instances in the same VPC, as well as with resources outside the VPC, such as the internet.

D. You can manually associate or disassociate a public IP address: This is true. You can manually associate or disassociate a public IP address with an instance at any time. When you associate a public IP address with an instance, it replaces any existing public IP address that was assigned to the instance. When you disassociate a public IP address from an instance, the instance still has a private IP address that can be used to communicate with other instances in the same VPC.

In summary, the incorrect statement in regards to public IP addressing in AWS is option B: "When an IP is disassociated from the instance, it is added back to the pool."