I think perhaps you are using an Atom Bomb to split a walnut. If your files are well formed and as simple as shown then something like this may be more appropriate:

#!/usr/bin/perl -w
use strict;
my $n;
local $/;
my $data =<DATA>;
for my $network( split /(?=network:\w+)/, $data ) {
     my ( $net_loc ) = $network =~ m/network:(\w+)/;
     my ( $ip ) = $network =~ m/ip\s*=\s*([\d\.]+)/;
     my ( $mask ) = $network =~ m/mask\s*=\s*([\d\.]+)/;
     my %hosts = $network =~ m/host:(\w+)\s*=\s*{\s*([^;}]+)/g;
     $n->{$net_loc} = { ip => $ip, mask => $mask };
     $n->{$net_loc}->{$_} = $hosts{$_} for keys %hosts;
}

use Data::Dumper;
print Dumper $n;

__DATA__
network:north = {
ip = 10.1.1.0; mask = 255.255.255.0;
host:asterix = {ip = 10.1.1.10;}
host:obelix = {ip = 10.1.1.11;}
host:idefix = {ip = 10.1.1.12;}
host:ix_13_20 = {range = 10.1.1.13 - 10.1.1.20;}
}

network:south = {
ip = 10.1.1.0; mask = 255.255.255.0;
host:asterix = {ip = 10.1.1.10;}
host:obelix = {ip = 10.1.1.11;}
host:idefix = {ip = 10.1.1.12;}
host:ix_13_20 = {range = 10.1.1.13 - 10.1.1.20;}
}

__END__
$VAR1 = {
          'north' => {
                       'ip' => '10.1.1.0',
                       'asterix' => 'ip = 10.1.1.10',
                       'obelix' => 'ip = 10.1.1.11',
                       'idefix' => 'ip = 10.1.1.12',
                       'mask' => '255.255.255.0',
                       'ix_13_20' => 'range = 10.1.1.13 - 10.1.1.20'
                     },
          'south' => {
                       'ip' => '10.1.1.0',
                       'asterix' => 'ip = 10.1.1.10',
                       'obelix' => 'ip = 10.1.1.11',
                       'idefix' => 'ip = 10.1.1.12',
                       'mask' => '255.255.255.0',
                       'ix_13_20' => 'range = 10.1.1.13 - 10.1.1.20'
                     }
        };
[download]

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

well, i do not feel very comfortable with grammars yet - you'll note this when my explanations start to get wacky ;) (to be honest, i hope i get some upvotes for formatting reasons ...)

the rule 'ip' nicely encloses a key=value pair, the same sort of rule can be applied to the mask. further, the name 'ip' is IMO not very well chosen, i rename it to 'ip_def'. finally, break the first regexp into its pieces, so you can specify whitespaces. the first rule gets:

network_object: 'network' ':' /(\w+)/ '=' '{' ip_def mask_def host(s) 
+'}'
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your problem with hosts_or_range is that you want to do too much within one rule. at first, it is irrelevant if a host has one ip or a whole range. so you can pull 'host:' one level up.

host        : 'host' ':' /\w+/ '=' '{' ip_or_range '}'
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if a host has an ip, it starts with the string 'ip'. if a host has an associated ip range, it starts with 'range' - and your problem disappears

ip_or_range : 'ip' '=' ip ';'
            | 'range' '=' ip '-' ip ';'
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in your grammar, the rule 'hosts_or_range' tries to do two jobs:

• there can be possible zero to inf hosts and
• each hosts associates either an ip or a range.

You have a number of errors in your grammar:

1. In the rule ip_nosemi, you forgot to backslash the last "</code>\d</code>".
2. In hosts_or_range, you have host(s?), when you probably meant to put the (s?) in network object.
3. You can't use $item as both a hash and an array in the same production!

I also reorganized your grammar a bit. It should work now, although I'm on a machine without PRD installed at the moment so you shouldn't just take my word on that. However, tachyon is right on this one; PRD is far too large of a hammer to use parse data like this. :)

startrule:       network_object(s)
network_object:  /network:(\w+)/ '=' '{'
                     'ip'   '=' ip
                     'mask' '=' ip
                     hosts_or_range(s?)
                 '}'
                 { print "Found network object named $item[1] ", 
                         "with IP $item[6] and MASK $item[9]\n"
                 }

hosts_or_range:  host | host_range
host_range:      /host:\w+/ '=' '{' 'range' '=' ip '-' ip    '}'
host:            /host:\w+/ '=' '{' 'ip'    '=' ip(s) '}'
ip:              / \d{1,3} (?:\.\d{1,3}){3} ;? /x
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