When you create a Virtual Private Cloud in EC2 using RightScale, you are allowed to configure multiple subnets within that cloud. From there, you can launch instances in any of the subnets you have created. The means for describing your IP space for each subnet is Classless Inter-Domain Routing or a CIDR block. CIDR is an excellent way to specify a subnet by using dotted quad IP and a subnet in a single compact string, without the more wasteful traditional netmasks (for example, a 255.255.255.0 netmask for a Class C internet address.) Of course, CIDR blocks also allow for more efficient use of IP addresses within the various Class A, B, or Class C internet addresses.
As an example, lets use a fictitious company LargeCorp.com, which has a Class B address with three subnets:
|LargeCorp.com||Traditional IP||Traditional Netmask||CIDR Block notation|
For those in need of further description of how the "/24" was arrived at with respect to the netmask portion of the CIDR block:
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