Here's a concise and organized summary of the key aspects of CIDR (Classless Inter-Domain Routing) and its application, particularly in AWS networking and security:
What is CIDR?
- Definition: CIDR is a method for allocating IP addresses and defining IP ranges.
- Purpose: It helps efficiently manage and allocate IP addresses by specifying an IP address followed by a slash (/) and a number, indicating the size of the address block.
Understanding CIDR Notation
- Components: CIDR notation has two parts: the base IP address and the subnet mask.
- Base IP: Usually the beginning of the IP range.
- Subnet Mask (/notation): Indicates how many bits of the IP address can vary, determining the size of the IP range.
Examples and Explanation
- /32: Represents a single IP address.
- 0.0.0.0/0: Represents all IP addresses.
- 192.168.0.0/26: Defines a range of 64 IP addresses.
Subnet Masks and IP Ranges
- /8 to /32: The subnet mask can range from /8, allowing a large range of IPs, to /32, which specifies a single IP.
- Calculating IP Ranges: The number after the slash (/) determines how many IP addresses are available in that range, with /24 allowing for 256 IPs (from .0 to .255).
Private vs. Public IPs
- IANA: The Internet Assigned Numbers Authority assigns certain blocks for private and public use.
- Private IP Ranges:
10.0.0.0/8: A large block used for large networks.172.16.0.0/12: Often used in default VPCs provided by AWS.192.168.0.0/16: Commonly seen in home networks for devices.
- Public IPs: All other IPs outside these ranges are considered public and are routable on the internet.
Practical Application