Welcome to the Monastery, deep27ak!

At a glance, it appears as though you've got numerous issues with your code, including undefined variables, an erroneous }, repeatedly reassigning over a variable without using it in loops etc.

Please post enough of a sample of the XML file you're using as input that will satisfy a single pass of the script. Without that, it's too time consuming to reconstruct the code properly.

Also, get in the habit of using proper indenting. It'll help you greatly, and it'll help us work with what you've got.

Here's an example:

use strict;
use warnings;
use XML::Simple;

my $xml = do {local $/='';'network.xml'} ;
my $servers = XMLin($xml, ForceArray => 1);
my %seen;

foreach my $server (@{$servers->{server}}) {

    my $brlist;
    my $corebrip;
    my $brmask;
    my $brip;
    my $num;
    my $brlan;

    my @node =  $server->{NodeName__1} . "\n";
    my $lanip = $server->{CoreLanIP_1__1}  ;
    my @mask = $server->{CoreLanNetmask_1} . "\n";

    my $network = join("/", $lanip, @mask);
    $network =~ s/.[0-9]*\//.0\//g;
    push(my @networklist, $network) if ! $seen{$network}++;
    $brlan = $server->{BRLAN} ;

    if ( $brlan eq "y" )  {
        $brip = $server->{BR_IP};
        $num = $server->{CoreLanNum} ."\n" ;
    }

    my  @brnwlist;

    for my $n (1..$num){
        $corebrip = $server->{'CoreLanIP_'.$n.'__1'} ;
        $brmask  = $server->{'CoreLanNetmask_'.$n} ."\n";
    }

    if ( $corebrip eq $brip ){

        $brlist = join ("/", $brip, $brmask) ;
        $brlist =~  s/.[0-9]*\//.0\//g;
        push( @brnwlist, $brlist) unless $seen{$brlist}++;
    }
    else {
        print "coreip doesnot matches brip\n";
    }
}

for $a (@brnwlist) {

    if ( $a ne "") {
        print "empty array";

        my $vnum = $server->{CoreVlanNum} ."\n" ;

        for my $i (1..$vnum){

            my $vlanip = $server->{'CoreVlan_IP_'.$i} ;
            my $vmask  = $server->{'CoreVlan_Netmask_'.$i} ."\n";

            if ($vlanip eq $brip){

                my $vlist = join ("/", $brip, $vmask) ;
                $vlist =~  s/.[0-9]*\//.0\//g;
                push(my @vnwlist, $vlist) if ! $seen{$vlist}++;
                print @vnwlist;
            }
        }
    }
}
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-stevieb