Update configuration-frontend-ip.md

Author: jaesoni

articles/application-gateway/configuration-frontend-ip.md

@@ -5,7 +5,7 @@ services: application-gateway
 author: greg-lindsay
 ms.service: application-gateway
 ms.topic: conceptual
-ms.date: 09/09/2020
+ms.date: 02/26/2023
 ms.author: greglin
 ---
 
@@ -33,6 +33,17 @@ Only one public IP address and one private IP address is supported. You choose t
 
 A frontend IP address is associated to a *listener*, which checks for incoming requests on the frontend IP.
 
+>[!NOTE] 
+> You can create private and public listeners with the same port number (Preview feature). However, be aware of any Network Security Group (NSG) associated with the application gateway subnet. Depending on your NSG's configuration, you may need an inbound rule with **Destination IP addresses** as your application gateway's public and private frontend IPs.
+> 
+> **Inbound Rule**:
+> - Source: (as per your requirement)
+> - Destination IP addresses: Public and Private frontend IPs of your application gateway.
+> - Destination Port: (as per listener configuration)
+> - Protocol: TCP
+> 
+> **Outbound Rule**: (no specific requirement)
+
 ## Next steps
 
 - [Learn about listener configuration](configuration-listeners.md)