What is the meaning of the "/" slash in such as the directive “allow from 000.111.222.333/444” in a .htaccess file?

Question

For example, I have these directives in my .htaccess file:

<Limit GET HEAD POST>
order deny,allow
allow from 1.37.0.0/16
allow from 23.226.128.240/31
allow from 23.234.68.64/27
allow from 23.234.80.200/29
allow from 23.234.91.160/27
deny from all
</Limit>

• What is the meaning of the "/" slashes therein?
• And how can we convert them into mod_rewrite directives?

Answer 1

That value defines the number of bits to mask off the most significant bits in the address. See the Wikipedia page on CIDR for more details.

For example, if I specify 10.0.0.0/8, that means 10.* is allowed (or denied, whatever hte case may be). That's because each octet in an IPv4 address has 8 bits (1 byte, a.k.a. octet). If I specify 192.168.0.0/24, that masks off the first 24 bits (first 3 octets) and 192.168.0.* is allowed or denied.