Hi farang,
The mySort routine looks like it's not doing it's job properly or efficiently..
Though, I don't know how the OP wants his/her data sorted, but really there is no need for the mySort subroutine. Because, all that that subroutine is doing can be done in a sort block like so:

use strict;
use warnings;

my %IP_Store = (
    "11.0.0.1"  => "UEH1_system_ip",
    "11.0.0.11" => "UEH11_system_ip",
    "11.0.0.3"  => "UEH25_system_ip",
    "11.0.0.25" => "UEH111_system_ip"
);

foreach my $Value (
    sort {
        $IP_Store{$a} =~ /(\d+)/;
        my $firstVal = $1;
        $IP_Store{$b} =~ /(\d+)/;
        my $secVal = $1;
        $firstVal <=> $secVal;
    } keys %IP_Store
  )
{
    print "$IP_Store{$Value}\n";
    print "System_ip = '$Value' \n";
}
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