The Ip Nat Outside Cisco command

The Cisco command 'ip nat outside' is used to configure the IP address and interface that will be used for outbound Network Address Translation (NAT). This command is typically used in conjunction with the 'ip nat inside' command, which specifies the IP address and interface used for inbound NAT. The 'ip nat outside' command allows network administrators to define the public IP address that will be used for outbound traffic from a private network.

Syntax:

ip nat outside interface-type interface-name [static | dynamic] ip-address

Parameters:

• interface-type: The type of interface to be used for outbound NAT. This can be one of the following:
  • ethernet
  • serial
  • dialer
  • frame-relay
  • async
  • tunnel
  • loopback
  • vlan
• interface-name: The name of the interface to be used for outbound NAT.
• static | dynamic: Specifies whether the IP address to be used for outbound NAT will be static or dynamic.
  • static: The IP address will be manually configured.
  • dynamic: The IP address will be obtained from a DHCP server.
• ip-address: The IP address to be used for outbound NAT.

Use Cases:

The 'ip nat outside' command is commonly used in the following scenarios:

• NAT Overload: This is a technique used to allow multiple private IP addresses to share a single public IP address. The 'ip nat outside' command is used to specify the public IP address that will be used for all outbound traffic from the private network.
• NAT Port Address Translation (PAT): This is a technique used to translate the port numbers used by private hosts to avoid port number conflicts when accessing public networks. The 'ip nat outside' command is used to specify the public IP address and port number that will be used for outbound traffic from the private network.
• Virtual Private Networks (VPNs): This is a technology that allows private networks to be interconnected over a public network. The 'ip nat outside' command is used to specify the public IP address that will be used for outbound traffic from the VPN.

Supported Devices:

The 'ip nat outside' command is supported on a wide range of Cisco devices, including routers, switches, and firewalls. The specific devices that support this command can vary depending on the IOS version being used.

Configuration Example:

The following is an example of how to configure the 'ip nat outside' command:

ip nat outside interface ethernet0/0 static 192.0.2.1

This command will configure the Cisco router to use the IP address 192.0.2.1 as the outbound NAT address for traffic originating from the Ethernet interface ethernet0/0.

Conclusion:

The 'ip nat outside' command is an essential tool for network administrators who need to configure NAT on Cisco devices. This command allows administrators to define the public IP address and interface that will be used for outbound traffic from a private network. The 'ip nat outside' command is supported on a wide range of Cisco devices and can be used in a variety of scenarios, including NAT overload, PAT, and VPNs.

ip nat outside Usage Examples

The Cisco command 'ip nat outside' is used to configure the IP address and interface that is used for Network Address Translation (NAT) outbound traffic. Here are some examples of how the 'ip nat outside' command can be used:

1. Configure an Outside Interface with a Static IP Address:

ip nat outside interface GigabitEthernet0/1 address 192.0.2.1

In this example, the 'ip nat outside' command is used to configure the GigabitEthernet0/1 interface as the outside interface for NAT. The static IP address 192.0.2.1 is assigned to this interface, which will be used as the source IP address for translated outbound traffic.

1. Configure an Outside Interface with a DHCP-Assigned IP Address:

ip nat outside interface GigabitEthernet0/1

When using a DHCP-assigned IP address for the outside interface, the 'address' parameter is not specified. In this case, the router will automatically obtain an IP address from the DHCP server and use it as the source IP address for NAT outbound traffic.

1. Configure an Outside Interface with a Range of IP Addresses:

ip nat outside interface GigabitEthernet0/1 range 192.0.2.10 192.0.2.20

This command configures the GigabitEthernet0/1 interface as the outside interface for NAT and specifies a range of IP addresses (192.0.2.10 to 192.0.2.20) that can be used as the source IP addresses for translated outbound traffic.

1. Configure an Outside Interface with a Specific Virtual IP Address:

ip nat outside interface GigabitEthernet0/1 virtual-address 192.0.2.1

In this example, the 'virtual-address' parameter is used to specify a specific virtual IP address (192.0.2.1) that will be used as the source IP address for translated outbound traffic. This is useful when you want to use a specific IP address for NAT, even if the outside interface has a different IP address.

1. Configure an Outside Interface with a Translated Port:

ip nat outside interface GigabitEthernet0/1 translated-port 80

The 'translated-port' parameter is used to specify a specific port number that will be used for translated outbound traffic. In this example, port 80 is specified, which is commonly used for HTTP traffic. This means that all outbound HTTP traffic will be translated to use port 80 on the outside interface.

These are just a few examples of how the 'ip nat outside' command can be used to configure NAT on a Cisco router. The specific configuration will depend on your network requirements and the desired behavior of NAT.