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Here you can find information about how IPs works in AWS: IP addressing documentation.
Is important to differentiate between the Private IPs and the Public IPs:
- Private IPs: are not reachable over the internet, and can be used for communication between the instances in your VPC. This are the ones that appears in your VPC, as these are just for internal use there is no overlapping issues with another accounts private IPs.
- Public IPs: These are the ones that give you access to the internet. So these are the ones that have to be unique.
Usually most of the resources in your VPC will have just private IPs and you will just a few Public IPs to provide access to the elements in your VPC to the internet.
I hope below explanation will give you an idea, how IPs are managed in AWS.
We create VPC in AWS with Private CIDR range.
Private IP can only allow certain values: • 10.0.0.0 – 10.255.255.255 (10.0.0.0/8) • 172.16.0.0 – 172.31.255.255 (172.16.0.0/12) <= default VPC included in this range. Most of the time default AWS VPC gets created in this range. • 192.168.0.0 – 192.168.255.255 (192.168.0.0/16)
All the rest of the IP on the internet are public IP.
Yes other accounts can create VPC with same CIDR range but that is private to their network. Well you cannot join those two VPCs/network/accounts because those are having overlapping CIDR and obviously creates conflicts.
AWS assigns private ip to resources from the CIDR range which is used to create VPC. You can choose specific private IP from CIDR range if you want.
And CIDR range 172.31.0.0/16, is quite big, it provides 65534 IP addresses.
Best Regards, Vikas
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