AWS Consulting Sydney

AWS VPC now allows addition of secondary CIDR blocks

AWS recently announced that we can now expand the IP range of a VPC after the VPC has been created. Great news!

We no longer need our previous blog about how to rebuild VPC to enlarge the CIDR block.

Let’s have a try with this new feature:

In AWS VPC console, select the VPC you want to change:

Next, find “Edit CIDRs” in the “Actions” list:

 

 

 

 

 

 

 

 

Add in the new CIDR you want. Each CIDR must be:

  1. Not overlapping with existing CIDRs in this VPC
  2. Smaller than /16 (i.e. /16~/28)
  3. Within the same large block (/8) of the initial CIDR
  4. Following normal AWS VPC CIDR rules

 

After clicking “Save,” the default route of VPC route tables will be updated automatically:

 

 

Now, our VPC has more accessible IPs without having to re-create the VPC:

 

Alternatively, you can do the same via CLI with below command:

(make sure you’ve updated your awscli tool to the latest version. Option “—cidr-block” is a new feature in “associate-vpc-cidr-block”)

aws ec2 associate-vpc-cidr-block –cidr-block 10.88.0.0/16 –vpc-id vpc-1xxxxxxxx

Please bear in mind, you many need to modify your NACLs and Security Groups if they are not default.

AWS official news about this feature can be found here:

https://aws.amazon.com/about-aws/whats-new/2017/08/amazon-virtual-private-cloud-vpc-now-allows-customers-to-expand-their-existing-vpcs/

 

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