title: Getting 'Must be valid Ipv4 CIDR' error after passing subnet's CIDR block
body: <p>I have created a VPC(public and private subnets) on AWS with IPV4 CIDR block as <code>10.0.0.0/26</code> (i.e. it can have 2^6 = 64 IP addresses along with one subnet address and one broadcast address). I want to create following two subnets but I am getting <code>Must be valid Ipv4 CIDR</code> error:</p>
  
  <ol>
  <li>A public subnet with <code>10.0.0.0/28</code> CIDR block, and</li>
  <li>A private subnet with <code>10.0.0.8/28</code> CIDR block</li>
  </ol>
  
  <p>If I am giving subnet mask as <code>/28</code> and I want to divide the addresses into two subnets, the address will fall in range <code>10.0.0.0 [10.0.0.00000000] - 10.0.0.15 [10.0.0.00001111]</code>. On the other hand, if I am giving CIDR block as <code>10.0.0.16/28</code>, I am not getting any error. Why AWS is giving <code>Must be valid Ipv4 CIDR</code> error with CIDR block as <code>10.0.0.8/28</code>? </p>