aws ec2 associate-subnet-cidr-block
Associates a CIDR block with your subnet. AWS CLI reference
4 options Its page in the AWS CLI reference
Options
--ipv6-cidr-blockThe IPv6 CIDR block for your subnet.--ipv6-ipam-pool-idAn IPv6 IPAM pool ID.--ipv6-netmask-lengthAn IPv6 netmask length.--subnet-idThe ID of your subnet.