Maybe something like:

my $data;
my $subnet;
my $ip = qr/((?:\d{1,3}\.){3}\d{1,3})/;

while(<DATA>){
        /subnet\s+$ip\s+netmask\s+$ip/ and 
          $subnet = $1 and $data->{"subnet:$subnet"} = {
            ip      => $1,
            mask    => $2,
        };
        /range\s+$ip\s+$ip/ and
          $data->{"subnet:$subnet"}{range} = {
            ip      => $1,
            mask    => $2,
        };
        /option\s+routers\s+$ip/ and
          $data->{"subnet:$subnet"}{routers} = {
            ip      => $1
        };
        /option\s+domain-name\s+"(\S+)"/ and 
          $data->{"subnet:$subnet"}{'domain-name'} = {
            'hostname', $1
        };
        /option\s+domain-name-servers\s+(.+?)\W*$/ and 
          $data->{"subnet:$subnet"}{'domain-name-servers'} = {
            'hostname', [ split /,/, $1 ]
        };
        /option\s+option-222\s+"(\S+)"/ and 
          $data->{"subnet:$subnet"}{'option-222'} = {
            'hostname', $1
        };
}

use Data::Dumper;die Dumper($data);


__DATA__

subnet 192.168.125.0 netmask 255.255.255.0 {
    range 192.168.125.200 192.168.125.250;
    option routers 192.168.125.10;
    option domain-name "pillepalle.de";
    option domain-name-servers 192.168.125.10, 192.168.101.15;
    option option-222 "http://pillepalle.de:8080";
}

__END__

stdout:

$VAR1 = {
          'subnet:192.168.125.0' => {
                                      'routers' => {
                                                     'ip' => '192.168.
+125.10'
                                                   },
                                      'ip' => '192.168.125.0',
                                      'domain-name-servers' => {
                                                                 'host
+name' => [
                                                                      
+           '192.168.125.10',
                                                                      
+           ' 192.168.101.15'
                                                                      
+         ]
                                                               },
                                      'domain-name' => {
                                                         'hostname' =>
+ 'pillepalle.de'
                                                       },
                                      'range' => {
                                                   'ip' => '192.168.12
+5.200',
                                                   'mask' => '192.168.
+125.250'
                                                 },
                                      'option-222' => {
                                                        'hostname' => 
+'http://pillepalle.de:8080'
                                                      },
                                      'mask' => '255.255.255.0'
                                    }
        };
[download]