It looks like that's what you asked for. I'm not sure what the problem is.

The problem is that i need every IP only once. (Sorry if i didn't say that before). So i only need to get the IPAddress and not also the NEIGHBOURIPAddress, bacause then i have everything only once.

If you ever need to get unique values in Perl then you should think about using a hash.

use XML::XPath;

my $xp = XML::XPath->new(filename => '/path/to/file');

my %seen;
foreach ('IP-ADDRESS', 'IP-NEIGHBOUR') {
  foreach my $ip ($xp->findnodes("//$_")) {
    my $addr = $ip->findvalue('.');
    print "$addr\n" unless $seen{$addr}++;
  }
}
[download]

--
<http://www.dave.org.uk>

"The first rule of Perl club is you do not talk about Perl club."
-- Chip Salzenberg

#
use XML::Dumper;

open (XMLINPUT, "e:/topo.xml")

or     (print "Die XML Datei konnte nicht geöffnet werden!!\n".
    "Bitte Pfad und Dateiname mit Slashs angeben!!".
    "\nz.B. c:/data1.xml\n" and
    open (MACERROR, ">XMLError.err") and
    print MACERROR     "Die XML Datei konnte nicht geöffnet werden!!\n
+".
            "Bitte Pfad und Dateiname mit Slashs angeben!!".
            "\nz.B. c:/data1.xml\n" and
    close MACERROR and
    exit);

# Zeiger erzeugen
$zeiger_xml = new XML::Dumper->xml2pl(join("",<XMLINPUT>));
$zeiger_data = \@{$zeiger_xml->{'Data'}};
close XMLINPUT;



open (CACHENEU, ">ips2.txt");
close CACHENEU;

foreach $z_device (@{$zeiger_xml->{'Device'}})
    {
        #if     (   $z_device->{'SystemDescription'} =~ m/Version 12.0
+\(5\)/
        #and $z_device->{'SystemDescription'} =~ m/C2900/
        #and $z_device->{'SystemDescription'} !~ m/WS/)
        #{
        open (CACHENEU, ">>ips2.txt");
        foreach $z_add (@{$z_device->{'DeviceName'}})
            {
            %PortHash = ( $z_device->{'DeviceName'} => $z_ip->{'IPAddr
+ess'} );
            printf CACHENEU ("%s\t\t%s\n",%PortHash);
            }
        close CACHENEU;
        #}
    }
print "\nfertig Portliste erstellen!!\n" ;
[download]

<?xml version="1.0" encoding="UTF-8" ?> 
- <CMData>
  <CMServer>S03</CMServer> 
  <CreatedAt>Tue Aug 24 09:09:41 GMT+02:00 2004</CreatedAt> 
  <SchemaVersion>1.0</SchemaVersion> 
  <Heading>Topology Data</Heading> 
- <Layer2Details>
- <Device>
  <DeviceName>LWL-H91-CW-4-5-4</DeviceName> 
  <IPAddress>148.192.59.254</IPAddress> 
<DeviceState>Reachable</DeviceState> 
  <DeviceType>C2950G-24</DeviceType> 
- <Neighbors>
- <Neighbor>
  <NeighborIPAddress>148.192.22.22</NeighborIPAddress> 
  <NeighborDeviceType>C6506</NeighborDeviceType> 
  <Link>Point to Point link</Link> 
  <LocalPort>Gi0/2</LocalPort> 
  <RemotePort>3/3</RemotePort> 
  </Neighbor>
[download]