diff -up e-smith-base-5.2.0/root/usr/lib/perl5/site_perl/esmith/console/configure.pm.checkIPOverlap e-smith-base-5.2.0/root/usr/lib/perl5/site_perl/esmith/console/configure.pm
--- e-smith-base-5.2.0/root/usr/lib/perl5/site_perl/esmith/console/configure.pm.checkIPOverlap	2008-08-20 23:17:24.000000000 +0200
+++ e-smith-base-5.2.0/root/usr/lib/perl5/site_perl/esmith/console/configure.pm	2009-10-24 20:32:00.000000000 +0200
@@ -1049,7 +1049,38 @@
     {
         if ( isValidIP($choice) )
         {
-            $db->set_value('ExternalNetmask', cleanIP($choice));
+            # Check for overlapping ranges in external and internal interface IP and netmasks
+
+            # Retrieve the local IP/mask setting
+            my $localAddress = $db->get_value('LocalIP');
+            my $localNetmask = $db->get_value('LocalNetmask');
+
+            # Retrieve the external IP/mask setting
+            my $externalAddress = $db->get_value('ExternalIP');
+            my $externalNetmask = cleanIP($choice);
+
+            if ( ipv4_in_network($localAddress, $localNetmask, $externalAddress, $externalNetmask) )
+            {
+
+                ($rc, $choice) = $console->message_page
+                (
+                    title => gettext("Invalid address ranges"),
+                    text  => gettext(
+                                 "Internal address range overlaps external address range" .
+                                 "\n\n".
+                                 "Local interface: $localAddress/$localNetmask" .
+                                 "\n" .
+                                 "External interface: $externalAddress/$externalNetmask" .
+                                 "\n\n".
+                                 "Please review your settings."
+                    )
+                );
+
+                goto STATIC_IP;
+
+            }
+
+            $db->set_value('ExternalNetmask', $externalNetmask);
             goto STATIC_GATEWAY;
         }
     }