#!/usr/bin/perl
use strict;
use warnings;

#### untested ####

open my $fh_transfile, '<', "filename" 
    or die "unable to open translation file $!";

my %table;

while my $line (<$fh_transfile>)
{
   my($nat_ip, $real_ip) = split ' ', $line;
   $table{$nat_ip} = $real_ip;
}
close $fh_transfile;


open my $fh_bigfile , '<', "filename" or die
    "unable to open big input file $!";
open my $fh_out, '>', "filenameout" or die
    "unable to open big output file $!"

while my $line (<$fh_bigfile>)
{
   chomp $line;
   my @tokens = split ',',$line;
   
   if ($table{$tokens[8]})
   {
       $tokens[8] = $table{$tokens[8]};
   }

   print $fh_out join(",",@tokens),"\n";
}