v4tov6migration

Question

Hello AWS Community,

I'm currently working on enabling IPv6 in our AWS VPC and have encountered a blocker. Here are the steps I've completed so far:

Enabled IPv6 in the VPC (added an IPv6 CIDR block).
Enabled IPv6 for some subnets (added IPv6 CIDR blocks).
However, I'm facing a problem:

I am unable to add IPv6 CIDR blocks to more than two subnets. When trying to add an IPv6 CIDR block, only two blocks are available, and these have already been used on other subnets.
As a result, I can only launch instances in subnets that already have an IPv6 CIDR block, which is limiting our deployment.
Here are my initial thoughts and questions that I need help with:

Is there a limit on the number of IPv6 CIDR blocks that can be assigned to subnets within a VPC?
Could this issue be related to account configuration or service quotas? We are currently only using Amazon-provided IPv6 CIDR blocks.
If there is a quota, is it possible to request an increase in the number of IPv6 CIDR blocks that can be assigned? If so, how can I go about this?
I have already tried adjusting the routing blocks and prefixes but to no avail. Any insights or guidance on how to resolve this would be greatly appreciated.

Thank you!

Accepted Answer

You can always add additional IPv6 CIDR blocks for up to total of 5 with /44 to /60 mask. Amazon provided default IPv6 is /56 which you are using in this scenario.

To associate IPv6 to your subnets there are three option you can use, you can associate an entire /56 block for 1 subnet or /60 block for 16 subnets or /64 block for 256 subnets.

Can you provide subnet masks that you are using for IPv6 CIDR in both of your subnets? 
Also, you can use https://www.cidr.eu/en/calculator or similar IPv6 subnet calculator for simplicity.

Answer

It sounds like you have one single /56 IPv6 CIDR block which is provided by Amazon by default. With this /56 block, you can create a subnet and associate an IPv6 CIDR block with the range of /60 or /64. To have more subnet associated with more IPv6 CIDR block, you need to add more IPv6 CIDR to the VPC. You can associate up to five IPv6 CIDR blocks from /44 to /60 in increments of /4. The quota is for the VPC is 5 but it's adjustable by requesting an increase.

v4tov6migration

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