diff --git a/README.md b/README.md
index 5f13daa..a287937 100644
--- a/README.md
+++ b/README.md
@@ -185,6 +185,26 @@
 
 iface br-lan inet6 static
     address fd99:23eb:1682::1/64
+
+# Optional
+# VLAN4: Compatibility Layer for /24 Devices
+auto br-compatdev
+iface br-compatdev inet static
+    bridge_ports eno1.4
+    bridge_stp off
+
+    bridge_hw 8f:5e:21:bc:9c:0b
+
+    address 10.3.0.1
+    netmask 255.255.255.0
+
+    # DNAT & allow established connections
+    post-up iptables -t nat -A POSTROUTING -o $IFACE -j MASQUERADE
+    post-up iptables -A FORWARD -i $IFACE -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
+    # remove rules
+    post-down iptables -t nat -D POSTROUTING -o $IFACE -j MASQUERADE
+    post-down iptables -D FORWARD -i $IFACE -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
+
 ```
 
 # 域名