Classless Inter-Domain Routing (CIDR)

Map Of Internet 1973


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


CIDR notation:

IP Address/prefix



The world


  • is the wildcard IP address that match any possible machines

Only one IP


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


How to find the CIDR of one IP ?

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


NetRange: -


Range to Cidr

In Postgress from numeric IP with inet_merge

        ''::inet + ip_from, 
        ''::inet + ip_to
from ip where ctry = 'NL';


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