def associate_subnet_cidr_block(SubnetId=None, Ipv6CidrBlock=None):
    """
    Associates a CIDR block with your subnet. You can only associate a single IPv6 CIDR block with your subnet. An IPv6 CIDR block must have a prefix length of /64.
    See also: AWS API Documentation
    
    
    :example: response = client.associate_subnet_cidr_block(
        SubnetId='string',
        Ipv6CidrBlock='string'
    )
    
    
    :type SubnetId: string
    :param SubnetId: [REQUIRED]
            The ID of your subnet.
            

    :type Ipv6CidrBlock: string
    :param Ipv6CidrBlock: [REQUIRED]
            The IPv6 CIDR block for your subnet. The subnet must have a /64 prefix length.
            

    :rtype: dict
    :return: {
        'SubnetId': 'string',
        'Ipv6CidrBlockAssociation': {
            'Ipv6CidrBlock': 'string',
            'Ipv6CidrBlockState': {
                'State': 'associating'|'associated'|'disassociating'|'disassociated'|'failing'|'failed',
                'StatusMessage': 'string'
            },
            'AssociationId': 'string'
        }
    }
    
    
    """
    pass
