diff --git a/gestion/gen_confs/firewall_crans.py b/gestion/gen_confs/firewall_crans.py
index 394c9b66..53aed0b7 100755
--- a/gestion/gen_confs/firewall_crans.py
+++ b/gestion/gen_confs/firewall_crans.py
@@ -135,10 +135,26 @@ class firewall_crans :
         remove_lock('firewall')
 
     def nat_table(self) :
-        print 'bla'
+	self.anim = anim('    Structure de la table nat')
+	for chaine in [ 'TEST_MAC-IP', 'RESEAUX_NON_ROUTABLES_SRC', 'RESEAUX_NON_ROUTABLES_DST' ] :
+	    iptables('-t nat -N %s' % chaine)
+	    
+	iptables("-t nat -P PREROUTING -j ACCEPT")
+	iptables("-t nat -A PREROUTING -i lo -j ACCEPT")
+	iptables("-t nat -A PREROUTING -d 224.0.0.0/4 -j DROP")
+	iptables("-t nat -A PREROUTING -j RESEAUX_NON_ROUTABLES_DST")
+	iptables("-t nat -A PREROUTING -j RESEAUX_NON_ROUTABLES_SRC")
+	iptables("-t nat -A PREROUTING -j TEST_MAC-IP")
+	iptables("-t nat -P PREROUTING DROP")
+	print OK
+	
+    def nat_table_tweaks(self) :
         return
-
     def filter_table(self) :
+	self.anim = anim('    Structure de la table filter')
+	print OK
+	
+    def filter_table_tweaks(self) :
         return
 
     def start_fw_funcs(self) :
@@ -177,10 +193,10 @@ class firewall_crans :
         cprint("     -> fin de la procédure de démarrage",'vert')
                 
     def __start(self) :
-        self.anim = anim('    Structure de la table nat')
         self.nat_table()
-        self.anim = anim('    Structure de la table filter')
+	self.nat_table_tweaks()
 	self.filter_table()
+	self.filter_table_tweaks
         
     def reseaux_non_routables(self) :
         """ Construction de RESEAUX_NON_ROUTABLES_{DST,SRC} """