use strict;
use XML::Rules;
use Data::Dumper;

my $parser = XML::Rules->new(
	rules => {
		_default => 'content',
		Variable => sub {$_[1]->{Name} => $_[1]->{Value}},
		IP => 'content array',
		'VariableConfig,ServerConfig' => 'no content',
		Server => 'no content by Name',
		Config => 'pass no content',
	},
);

my $data = $parser->parse(\*DATA);
print Dumper($data);

my @FQDNs = map {$_->{FQDN}} values %{$data->{ServerConfig}};
print "@FQDNs";

__DATA__
<Config>
  <VariableConfig>
      <Variable>
        <Name>NAME</Name>
        <Value>somevalue</Value>
      </Variable>
      <Variable>
        <Name>NAME2</Name>
        <Value>somevalue blah</Value>
      </Variable>
  </VariableConfig>
  <ServerConfig>
     <Server>
        <Name>blue</Name>
        <IP>xxx.xxx.xxx.xx</IP>
        <IP>xxx.xxx.xxx.xx</IP>
        <FQDN>blue.some.domain</FQDN>
     </Server>
     <Server>
        <Name>black</Name>
        <IP>xxx.xxx.xxx.xx</IP>
        <IP>xxx.xxx.xxx.xx</IP>
        <FQDN>black.some.domain</FQDN>
     </Server>
  </ServerConfig>
</Config>