Configuring NAT

Configuring NAT
In this section, we will talk about the commands needed for the following NAT configurations:
 Static NAT
 Dynamic NAT
Configuring NAT 89
 Using overloading for NAT
 TCP load distribution
 Translation of overlapping addresses
We will also cover how to verify NAT operations, troubleshoot NAT problems, and clear
NAT translation entries. First, let’s talk about what all these configurations have in common.
Each interface involved in the NAT process must be designated either an inside or outside
interface, but not both at the same time. There must be at least one interface on the router configured
as inside and at least one configured as outside. This way the router knows how to handle
inbound and outbound traffic on an interface. In this example, the Ethernet0 interface is the
inside and the Serial0 interface is the outside. The ip nat inside and ip nat outside commands
must be used from interface configuration mode to tell the router which interface is performing
which role in the NAT process. The following commands show how to configure our
example router:
Border(config)#interface ethernet0
Border(config-if)#ip nat inside
Border(config-if)#exit
Border(config)#interface serial0
Border(config-if)#ip nat outside
Border(config-if)#exit
Border(config)#
As you can see from the following excerpt from the router configuration, the interfaces have
been designated as inside and outside:
!
interface Ethernet0
ip address 10.1.2.254 255.255.255.0
ip nat inside
!
interface Serial0
ip address 200.1.1.1 255.255.255.0
ip nat outside
!