CIDR

They help to define an [[IP address range]]
- We've seen WW.XX.YY.ZZ/32 == one [[IP]]
- We've seen 0.0.0.0/0 == all IPs
- But we can define 192.168.0.0/26: 192.168.0.0-192.168.0.63 (64 IPs)

Understanding CIDR¶

A CIDR has two components
- The base IP (XX.XX.XX.XX)
- The [[Subnet Mask]] (/26)
The base IP represents an IP contained in the range
The [[subnet mask]]s defines how many bits can change in the IP
The subnet mask can take two forms. Examples:
- 255.255.255.0 (less common)
- /24 (more common)

The subnet masks basically allows part of the underlying IP to get additional next values from the base IP
/32 allows for 1 IP = 2^0
/31 allows for 2 IP = 2^1
/30 allows for 4 IP = 2^2
/29 allows for 8 IP = 2^3
/28 allows for 16 IP = 2^4
/27 allows for 32 IP = 2^5
/26 allows for 64 IP = 2^6
/25 allows for 128 IP = 2^7
/24 allows for 256 IP = 2^8
/16 allows for 65,536 IP = 2^16
/0 allows for all IPs = 2^32

The [[Internet Assigned Numbers Authority]] (IANA) established certain blocks of [[IPv4]] addresses for the use of private ([[LAN]]) and public ([[internet]]) addresses.
Private IP can only allow certain values
- 10.0.0.0 - 10.255.255.255 (10.0.0.0/8) - in big networks
- 172.16.0.0 - 172.31.255.255 (172.16.0.0/12) - default AWS one
- 192.168.0.0-192.168.255.255 (192.168.0.0/16) - example: home networks
All the rest of the IP one the internet are public IPs