CIDR Block

CIDR to IPv4 |

Classless Inter-Domain Routing

• CIDR notation represents an IP address range as a base IP address followed by a forward slash and a number that represents the number of bits used for the network prefix.

  • Ex: 192.168.0.0/16

• Subnet CIDR block can not be overlapped

• CIDR can not change. Plan ahead.

• Netmask: determine the number of IPs that are available for the network.

quick memo

Special cases

• CIDR naming convention 0.0.0.0/0 represents all IPv4 addresses. ::/0 for IPv6

• 192.168.0.0/16 : Home network

• 172.16.0.0/12 : AWS default VPC

• 10.0.0.0/8 : big network