In AWS EC2, while configuring a security group, the user needs to specify the IP address in CIDR notation. The CIDR IP range 10.20.30.40/32 says it is for a single IP 10.20.30.40. If the user specifies the IP as 10.20.30.40 only, the security group will not accept and ask it in a CIDR format. Reference: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-network-security.html