How do I modify the IPv4 CIDR block of my Amazon VPC?
I want to change the IPv4 CIDR block of my Amazon Virtual Private Cloud (Amazon VPC).
Short description
It's not possible to change or modify the IP address range of an existing virtual private cloud (VPC) or subnet. However, you can do one of the following:
- Add an additional IPv4 CIDR block as a secondary CIDR to your VPC.
- Create a new VPC with your preferred CIDR block and then migrate the resources from your old VPC to the new VPC (if applicable).
Resolution
Add a secondary IPv4 CIDR block to your VPC
To extend the IPv4 address range of your VPC, see Add or remove a CIDR block from your VPC. Make sure that you follow the CIDR block association restrictions.
If your depleted CIDR block is a secondary CIDR block, then associate another CIDR block with a new IP address range.
Note: By default, a local route is added to all routing tables in the VPC for every CIDR block associated with the VPC. This allows you to route traffic between the primary and secondary CIDR resources without additional routing. To restrict unintended traffic, use security groups and network access control lists (network ACLs).
Create a new VPC with a different IPv4 CIDR block and migrate your resources (if applicable)
If extending your VPC's IP address range with an additional IPv4 CIDR block isn't an option, you can create a new VPC with your preferred IPv4 CIDR block. Then, manually migrate all of your existing resources to the new VPC (if applicable).
Note: After you complete migrating all of the resources to your new VPC, you can delete all underlying resources in your old VPC. You can delete all of the following:
- Terminating all instances running in the VPC.
- Deleting all security groups associated with the VPC (except the default one).
- Deleting all route tables associated with the VPC (except the default one),
- Deleting any other resources as needed.
After you delete the underlying resources, you can delete your old VPC.
Related information
How do I move my EC2 instance to another subnet, Availability Zone, or VPC?
How do I change the VPC for an Amazon RDS DB instance?
I tried to delete my Amazon VPC, but I received a dependency error. How can I delete my Amazon VPC?
Blocked using option 1
I was following the first option Add an additional IPv4 CIDR block as a secondary CIDR. Where in current VPC we have AZ1 and AZ2, so I added a secondary CIDR block to have a AZ3, but here I'm running into an issue in exportVpc function, its not able to update the subnet IDs for the AZ3, as it says that the export VpcSubnetIds cannot be updated as it is already in use by Load balancer.
As we are doing changes in production, we cannot delete the existing Load balancer. So is there a way where we can export the AZ3 and update load balancer to have all the 3 AZs.
Thank you for your comment. We'll review and update the Knowledge Center article as needed.
I think the first solution is Good, but this does not support automation if you see here in resource "Type" : "AWS::EC2::VPCCidrBlock", CIDRBLOCK is a string and it will not support an array please implement an api for this resource "AWS::EC2::VPCCidrBlock" to support both CIDR and automation
Thank you for your comment. We'll review and update the Knowledge Center article as needed.
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