How to get CIDR for a host/domain

From a linux terminal just run:

$ host facebook.com
facebook.com has address 173.252.120.68
facebook.com has IPv6 address 2a03:2880:2130:7f20:face:b00c:0:25de
facebook.com mail is handled by 10 msgin.vvv.facebook.com.
$ whois 173.252.120.68 | grep CIDR
CIDR:           173.252.64.0/18 

and that is it.

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