Associates a CIDR block with your subnet.Show details from next link. https://docs.aws.amazon.com/ja_jp/cli/latest/reference/ec2/associate-subnet-cidr-block.html
| aws ec2 associate-subnet-cidr-block --subnet-id |
| Enabling IPv6 on existing VPCs and subnets – cloudiamo.com : http://cloudiamo.com/2017/02/14/enabling-ipv6-on-existing-vpcs-and-subnets/ |
| aws ec2 associate-subnet-cidr-block --subnet-id subnet-5f46ec3b --ipv6-cidr-block 2001:db8:1234:1a00::/64 |
| disassociate-vpc-cidr-block — AWS CLI 1.16.6 Command Reference : http://docs.aws.amazon.com/cli/latest/reference/ec2/associate-subnet-cidr-block.html |