php cidr

Are you talking about the RFC?
http://rfc-ref.org/RFC-TEXTS/1518/longList.html

If so, please tell us why you need this information and show us what you have tried to use to get it, thanks.

yes

I try to use who.is to get this information because one of my client want to block all online proxy so he ask me ban it by ip i desiced to ban it by cidr.

whois is definitely not the proper tool for various reasons
- the information it provides is never up to date
- it is very likely that thousands of sites will correspond the the same whois entry

if you have a list of websites, you probably can simply perform a DNS lookup and insert each ip of each site as a /32 in the list
if you are using a firewall, it is very likely that the firewall can accept fqdn names and perform the lookup by itself

what is your original list ?
what tool are you using to block traffic ?

i use iptables to block the original list is list of websites and their ip

so i can block by websites too for example -d www.abc.com --dport 80 and it will block it

yes : this is the simple straightforward solution providing you have the list of sites you need to block.

the firewall should be intelligent enough not to perform dns queries too often, and intelligent enough too reperform them periodically in case the ips change.
actually i cannot confirm netfilter performs the queries when needed, but most firewalls do.