Lesson 46: Configuring PAT (NAT Overload)

PAT (Port Address Translation), also known as NAT Overload, is the most common configuration. It allows thousands of private hosts to share a single public IP address.

PAT Configuration Steps

1. Identify Inside and Outside Interfaces: Define which interface faces the private network and which faces the public Internet.
2. Define the Traffic to be Translated: Use an Access Control List (ACL) to specify which inside addresses are allowed to be translated.
3. Apply the Translation Logic: Use the public interface IP as the inside global address, overloading it.

ios ! Step 1: Interface Definitions Router(config)# interface GigabitEthernet 0/0 Router(config-if)# ip nat inside Router(config)# interface GigabitEthernet 0/1 Router(config-if)# ip nat outside

! Step 2: Define traffic to be translated (ACL 1 allows 192.168.1.0/24) Router(config)# access-list 1 permit 192.168.1.0 0.0.0.255

! Step 3: Apply PAT, using the outside interface IP, enabling overload Router(config)# ip nat inside source list 1 interface GigabitEthernet 0/1 overload

Verification

• show ip nat translations: Shows the active mapping table (inside local IP/port mapped to outside global IP/port).
• clear ip nat translation *: Clears the dynamic NAT table entries.