title: What format to use when entering an IP address into an EC2 Security Group rule?
body: <p>I am trying to configure secure ssh connection from bastion host (located in public subnet) to private linux instances (located in private subnet) in the same VPC.</p>
  
  <p>When I add a security group rule for my private linux instance, initially it shows the rule as:</p>
  
  <p><a href="https://i.stack.imgur.com/czrPy.png" rel="noreferrer"><img src="https://i.stack.imgur.com/czrPy.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/VUCKT.png" rel="noreferrer"><img src="https://i.stack.imgur.com/VUCKT.png" alt="enter image description here"></a> </p>
  
  <p>Please note that before adding the IP address of the bastion host, the water mark shows "CIDR, IP or Security Group", but when I add the IP address of the bastion host, it throws error as:</p>
  
  <blockquote>
    <p>The source needs to be a CIDR block or a Security Group ID.</p>
  </blockquote>
  
  <p>Why is not allowing me to enter the IP address of the bastion host here?</p>