The London Perl and Raku Workshop takes place on 26th Oct 2024. If your company depends on Perl, please consider sponsoring and/or attending.


Net::IP::Match::Regexp - Efficiently match IP addresses against ranges


Copyright 2005-2006 Clotho Advanced Media, Inc., <>

Copyright 2007-2008 Chris Dolan, <>

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.


    use Net::IP::Match::Regexp qw( create_iprange_regexp match_ip );
    my $regexp = create_iprange_regexp(
       qw( )
    if (match_ip('', $regexp)) {


This module allows you to check an IP address against one or more IP ranges. It employs Perl's highly optimized regular expression engine to do the hard work, so it is very fast. It is optimized for speed by doing the match against a regexp which implicitly checks the broadest IP ranges first. An advantage is that the regexp can be computed and stored in advance (in source code, in a database table, etc) and reused, saving much time if the IP ranges don't change too often. The match can optionally report a value (e.g. a network name) instead of just a boolean, which makes module useful for mapping IP ranges to names or codes or anything else.


This module does not yet support IPv6 addresses, although that feature should not be hard to implement as long as the regexps start with a 4 vs. 6 flag. Patches welcome. :-)

This module only accepts IP ranges in a.b.c.d/x (aka CIDR) notation. To work around that limitation, I recommend Net::CIDR::Lite to conveniently convert collections of IP address ranges into CIDR format.

This module makes no effort to validate the IP addresses or ranges passed as arguments. If you pass address ranges like 1000.0.0.0/300, you will probably get weird regexps out.


create_iprange_regexp($iprange | $hashref | $arrayref, ...)

This function digests IP ranges into a regular expression that can subsequently be used to efficiently test single IP addresses. It returns a regular expression string that can be passed to match_ip().

The simple way to use this is to pass a list of IP ranges as aaa.bbb.ccc.ddd/n. When used this way, the return value of the match_ip() function will be simply 1 or undef.

The more complex way is to pass a hash reference of IP range => return value pairs. When used this way, the return value of the match_ip() function will be the specified return value or undef for no match.

For example:

    my $re1 = create_iprange_regexp('', '');
    print match_ip('', $re1); # prints '1'
    my $re2 = create_iprange_regexp({'' => '',
                                     '' => 'localhost'});
    print match_ip('', $re2); # prints ''

Be aware that the value string will be wrapped in single quotes in the regexp. Therefore, you must double-escape any single quotes in that value. For example:

    create_iprange_regexp({'' => 'O\\'Reilly publishing'});

Note that the scalar and hash styles can be mixed (a rarely used feature). These two examples are equivalent:

                          {'' => ''},
                          {'' => 'LAN'});
    create_iprange_regexp({'' => 1,
                           '' => '',
                           '' => 1,
                           '' => 'LAN'});

If any of the IP ranges are overlapping, the broadest one is used. If they are equivalent, then the first one passed is used. If you have some data that might be ambiguous, you pass an arrayref instead of a hashref, but it's better to clean up your data instead! For example:

    my $re = create_iprange_regexp(['' => 'zero', '' => 'one']);
    print match_ip('', $re));   # prints 'zero', since both match

WARNING: This function does no checking for validity of IP ranges. It happily accepts 1000.0.0.0/-38 and makes a garbage regexp. Hopefully a future version will validate the ranges, perhaps via Net::CIDR or Net::IP.

create_iprange_regexp_depthfirst($iprange | $hashref | $arrayref, ...)

Returns a regexp in matches the most specific IP range instead of the broadest range. Example:

    my $re = create_iprange_regexp_depthfirst({'' => 'LAN',
                                               '' => 'router'});
    match_ip('', $re);

returns 'router' instead of 'LAN'.

match_ip($ipaddr, $regexp)

Given a single IP address as a string of the form aaa.bbb.ccc.ddd and a regular expression string (typically the output of create_iprange_regexp()), this function returns a specified value (typically 1) if the IP is in one of the ranges, or undef if no ranges match.

See create_ipranges_regexp() for more details about the return value of this function.

WARNING: This function does no checking for validity of the IP address.


There are several other CPAN modules that perform a similar function. This one is comparable to or faster than the other ones that I've found and tried. Here is a synopsis of those others:


Optimized for speed by taking a "source filter" approach. That is, it modifies your source code at run time, kind of like a C preprocessor. A huge limitation is that the IP ranges must be hard-coded into your program.


(Also released as Net::IP::CMatch)

Optimized for speed by doing the match in C instead of in Perl. This module loses efficiency, however, because the IP ranges must be re-parsed every invocation.


Uses Net::IP::Match::XS to implement a range-to-name map.


I ran a series of test on a Mac G5 with Perl 5.8.6 to compare this module to Net::IP::Match::XS. The tests are intended to be a realistic net filter case: 100,000 random IP addresses tested against a number of semi-random IP ranges. Times are in seconds.

    Networks: 1, IPs: 100000
    Test name              | Setup time | Run time | Total time 
    Net::IP::Match::XS     |    0.000   |  0.415   |    0.415   
    Net::IP::Match::Regexp |    0.001   |  1.141   |    1.141   
    Networks: 10, IPs: 100000
    Test name              | Setup time | Run time | Total time 
    Net::IP::Match::XS     |    0.000   |  0.613   |    0.613   
    Net::IP::Match::Regexp |    0.003   |  1.312   |    1.316   
    Networks: 100, IPs: 100000
    Test name              | Setup time | Run time | Total time 
    Net::IP::Match::XS     |    0.000   |  2.621   |    2.622   
    Net::IP::Match::Regexp |    0.024   |  1.381   |    1.405   
    Networks: 1000, IPs: 100000
    Test name              | Setup time | Run time | Total time 
    Net::IP::Match::XS     |    0.003   | 20.910   |   20.912   
    Net::IP::Match::Regexp |    0.203   |  1.514   |    1.717   

This test indicates that ::Regexp is faster than ::XS when you have more than about 50 IP ranges to test. The relative run time does not vary significantly with the number of singe IP to match, but with a small number of IP addresses to match, the setup time begins to dominate, so ::Regexp loses in that scenario.

To reproduce the above benchmarks, run the following command in the distribution directory:

   perl benchmark/ -s -n 1,10,100,1000 -i 100000


The speed of this module comes from the short-circuit nature of regular expressions. The setup function turns all of the IP ranges into binary strings, and mixes them into a regexp with | choices between ones and zeros. This regexp can then be passed to the match function. When an unambiguous match is found, the regexp sets a variable (via the regexp $LAST_REGEXP_CODE_RESULT, aka $^R, feature) and terminates. That variable becomes the return value for the match, typically a true value.

Here's an example of the regexp for a single range, that of the subnet:

    print create_iprange_regexp('')'
    # ^41101000111111001101000110(?{'1'})

If we add another range, say a NAT LAN, we get:

    print create_iprange_regexp('', '')'
    # ^4110(?>0000010101000(?{'1'})|1000111111001101000110(?{'1'}))

Note that for a 192.168.x.x address, the regexp checks at most the first 16 bits (1100000010101000) whereas for a 209.249.163.x address, it goes out to 25 bits (1101000111111001101000110). The cool part is that for an IP address that starts in the lower half (say only needs to check the first bit (0) to see that the regexp won't match.

If mapped return values are specified for the ranges, they get embedded into the regexp like so:

    print create_iprange_regexp({'' => '',
                                 '' => 'localhost'})'
    # ^4110(?>0000010101000(?{'localhost'})|1000111111001101000110(?{''}))

This could be implemented in C to be even faster. In C, it would probably be better to use a binary tree instead of a regexp. However, a goal of this module is to create a serializable representation of the range data, and the regexp is perfect for that. So, I'll probably never do a C version.


Because this module relies on the (?{ code }) feature of regexps, it won't work on old Perl versions. I've successfully tested this module on Perl 5.6.0, 5.8.1 and 5.8.6. In theory, the code regexp feature should work in 5.005, but I've used our and the like, so it won't work there. I don't have a 5.005 to test anyway...

Update from Oct 2008: I no longer keep a 5.6.0 around, so I rely on to tell me when this breaks for older Perls.


This module has 100% code coverage in its regression tests, as reported by Devel::Cover via perl Build testcover.

This module passes Perl Best Practices guidelines, as enforced by Perl::Critic v1.093.


Chris Dolan

I originally developed this module at Clotho Advanced Media Inc. Now I maintain it in my spare time.

ACKNOWLEDGMENTS inspired and subsidized development of the original version of this module.

Chris Snyder contributed a valuable and well-written bug report about handling missing mask values.

Michael Aronsen of suggested the depth-first matching feature.