#!/usr/bin/perl
use strict;
use XML::Simple;
use Net::Netmask;

my @block;
my %seen;
my $xml = do {local $/='';<DATA>} ;
my $servers = XMLin($xml, ForceArray => 1);

foreach my $server (@{$servers->{server}}) {
  my $br_ip = $server->{BR_IP};
  my $num   = $server->{CoreLanNum};
  #print "Searching for $br_ip\n";;
  for my $n (1..$num){
    my $ip = $server->{'CoreLanIP_'.$n.'__1'};
    if ($ip eq $br_ip){
      my $mask = $server->{'CoreLanNetmask_'.$n};
      # do what you want here with $n $ip or $mask
      my $block = new Net::Netmask($ip,$mask);
      push @block,$block unless $seen{$block}++;
    }
  }
}

print $_."\n" for @block;

__DATA__
<xml>
<server NodeName__1="blr92-nds-rds"
CoreLanNum="8"
CoreLanIP_1__1="192.169.72.3"
CoreLanNetmask_1="255.255.255.0"
CoreLanIP_2__1="192.169.72.3"
CoreLanIP_3__1="192.169.75.1"
CoreLanNetmask_3="255.255.255.0"
CoreLanIP_4__1="192.169.75.1"
CoreLanNetmask_4="255.255.255.0"
CoreLanIP_5__1="192.169.74.1"
CoreLanNetmask_5="255.255.255.0"
CoreLanIP_6__1="192.169.74.1"
CoreLanNetmask_6="255.255.255.0"
BR_IP="192.169.73.3"
BRLAN="y"
CoreLanIP_7__1="192.169.73.3"
CoreLanNetmask_7="255.255.255.0"
CoreLanIP_8__1="192.169.73.3"
CoreLanNetmask_8="255.255.255.0"
RouteIP_1__1="192.169.75.0"
RouteNetmask_1__1="255.255.255.0">
</server>
</xml>