NAT and PAT configuration on Router

 Network Address Translation (NAT) and Port Address Translation (PAT) are typically configured on routers and firewalls rather than on switches. These technologies are used to allow multiple internal devices to share a single public IP address to access resources on the internet. Switches, on the other hand, primarily operate at the data link layer (Layer 2) and do not perform NAT or PAT functions.

However, if you have a Cisco router connected to a switch and you want to configure NAT or PAT on that router to provide internet access to devices connected to the switch, here are the commands to do so:

Use Case: Assume you have a Cisco router with an Ethernet interface connected to a switch. You want to configure NAT or PAT on the router to allow devices connected to the switch to access the internet using a single public IP address.

1. Access Configuration Mode:

• Description: Access the router's command-line interface (CLI) and enter configuration mode.

bash
Router> enable
Router# configure terminal

2. Configure NAT or PAT:

• Description: Configure either NAT or PAT based on your requirements.

NAT (Dynamic NAT):

bash
Router(config)# ip nat inside source list access-list-number pool pool-name
Router(config)# interface interface_type interface_number
Router(config-if)# ip nat inside

PAT (Overloading):

bash
Router(config)# interface interface_type interface_number
Router(config-if)# ip nat inside
Router(config-if)# exit
Router(config)# interface interface_type interface_number
Router(config-if)# ip nat outside

• Description:
  • For NAT, you'll need to create an access control list (ACL) specifying the internal addresses that should be translated.
  • For PAT, you typically configure the inside and outside interfaces, and PAT is applied automatically to all inside devices.

3. Create Access Control List (NAT Only):

• Description: If you are configuring NAT, you'll need to create an ACL specifying the internal addresses to be translated.

bash
Router(config)# access-list access-list-number permit source source-wildcard

• Example:

bash
Router(config)# access-list 10 permit 192.168.1.0 0.0.0.255

4. Verify the NAT/PAT Configuration:

• Description: To verify the NAT or PAT configuration on the router, you can use the following commands:

bash
Router# show ip nat translations
Router# show ip nat statistics

• Description: These commands display information about the current NAT or PAT translations and statistics.

5. Save the Configuration:

• Description: After configuring NAT or PAT, be sure to save the configuration to the startup configuration to ensure it persists after a reboot.

bash
Router# write memory

In this use case, the router is configured to perform NAT or PAT functions to allow devices connected to the switch to access the internet using a single public IP address. The switch itself does not perform NAT or PAT; it's the router connected to the switch that handles these tasks.