Classless Inter-Domain Routing (CIDR)

About

Classless Inter-Domain Routing (CIDR) is a notation that defines a subnet (ip net range)

It is an integer that specifies the number of significant bits in the mask.

• between 0 and 32 inclusive for IPv4
• between 0 or 128 inclusive for IPv6

Syntax

CIDR notation:

IP Address/prefix

where:

• IP Address is a What is a IP Address? A Unique network IDentifier
• prefix is the subnet mask prefix length.

Example

The world

0.0.0.0/0

where:

• 0.0.0.0 is the wildcard IP address that match any possible machines

Only one IP

x.x.x.x/32

where the routing prefix 32 means that there is only one host on this network.

Example:

143.176.206.82/32

How to find the CIDR of one IP ?

In a whois request, you can see the CIDR back.

Example:

whois 172.70.250.60

NetRange:       172.64.0.0 - 172.71.255.255
CIDR:           172.64.0.0/13

Operation

Range to Cidr

In Postgress from numeric IP with inet_merge

SELECT 
    inet_merge(
        '0.0.0.0'::inet + ip_from, 
        '0.0.0.0'::inet + ip_to
   ) 
from ip where ctry = 'NL';

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