Let MySQL do all the work:
An IP address is simply a 32-bit number. It can be converted to it's numerical equivalent a little like this: 
my @octets=split(/\./,$ip_address);
my $numerical_address=($octets[3]+(255*$octets[2])+(65535*$octets[1])+
+(16777216*$octets[0]));

[download]
Store this in your database as a 32-bit integer, which is much more eficient than an 18-byte character field for IP address.
Then, to see if another IP address is in the same class C, do something like this: 
SELECT count(*) from table WHERE (int(ip/256)*256) = (int($ip_address_
+to_be_compared_to/256)*256)

[download]
Any result greater than 0 is a hit.
Note that the figure of 256 is for a class C subnet. It can be changed to suit any subnet mask you want to use.
Edit: Oops, that should be 256, not 255.....

In reply to Re: blocking last ip octet by leighsharpe
in thread blocking last ip octet by iluvperl

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.