#!/usr/bin/perl

    use warnings;
    use strict;

    use File::Tail;

    # monitor the leases database, waiting for new entries

    my $leases_db = File::Tail->new("/var/lib/dhcp/dhcpd.leases");

    # wait for entries of the following form:
    #
    #     lease 192.168.0.1 {
    #             starts 1 2004/09/27 14:16:02;
    #             ends 1 2004/09/27 15:16:02;
    #             hardware ethernet 00:0b:db:13:e7:49;
    #     }


    while (defined( $_ = $leases_db->read )) {
        my $ip_addr = $1 if /^lease ([.0-9]+)/i;
        if (/hardware ethernet ([:0-9a-f]+)/i) {
            my $mac_addr = $1;
            check_authorization($ip_addr, $mac_addr);
        }
    }

    # the following subroutine will be called when a new
    # lease record appears in the DHCP server's database

    sub check_authorization {
        my ($ip_addr, $mac_addr) = @_;
        # look up $mac_addr in authorization database
        # and take action if necessary
    }