diff --git a/files/interfaces-troisdorf4.j2 b/files/interfaces-troisdorf4.j2
index ff9d7f1..c1c7fea 100644
--- a/files/interfaces-troisdorf4.j2
+++ b/files/interfaces-troisdorf4.j2
@@ -24,6 +24,10 @@ iface {{ sn_interface_name }} inet static
         post-up iptables -A OUTPUT -o $IFACE -d 172.16.0.0/12 -j DROP
         post-up iptables -A OUTPUT -o $IFACE -d 169.254.0.0/16 -j DROP
         post-up iptables -A OUTPUT -o $IFACE -d 192.168.0.0/16 -j DROP
+        post-up iptables -A FORWARD -o $IFACE -d 10.0.0.0/8 -j DROP
+        post-up iptables -A FORWARD -o $IFACE -d 172.16.0.0/12 -j DROP
+        post-up iptables -A FORWARD -o $IFACE -d 169.254.0.0/16 -j DROP
+        post-up iptables -A FORWARD -o $IFACE -d 192.168.0.0/16 -j DROP
         post-up iptables -t nat -A POSTROUTING -o $IFACE -j MASQUERADE
 auto 6to4
         iface 6to4 inet6 6to4