Since version 12.3(14)T, Cisco introduced a new feature. Nat Virtual Interface ( NVI for short). It removes the need of specifying inside and outside interfaces. We configure the interface for use or not use NAT.

This makes easier translation configurations on the devices. Using the older version we did this kind of configurations:

Router(config)# int f0/0  
Router(config-if)# ip nat outside  
Router(config-if)# exit  
Router(config)# int f0/1  
Router(config-if)# ip nat inside  
Router(config-if)# exit  
Router(config)# ip nat inside source static 172.17.172.17 10.100.10.100

Now, with this feature:

Router(config)# int f0/0  
Router(config-if)# ip nat enable  
Router(config-if)# exit  
Router(config)# int f0/1  
Router(config-if)# ip nat enable  
Router(config-if)# exit  
Router(config)# ip nat source static 172.17.172.17 10.100.10.100

As we can see, we could use interface ranges, just in case we need more interfaces with NAT enabled so we can configure all with only one command:

Router(config)# int range fo/0 -1  
Router(config-if)# ip nat enable

Now, although is very easy, will see how to configure different kinds of translations using the new command set. I will not show the old way because there’s already a post in this blog.

Static NAT

Router(config)# ip nat source static 172.17.172.17 10.100.10.100  
Dynamic NAT  
 
Router(config)# ip nat pool dynpool 10.100.10.1 10.100.10.16 prefix-length
29  
Router(config)# ip access-l stan lan_nat  
Router(config-std-acl)# permit 172.17.0.0 0.0.0.15  
Router(config-std-acl)# exit  
Router(config)# ip nat source list lan_nat pool dynpool

Static PAT

Router(config)# ip nat source static tcp 172.17.172.17 80 10.100.10.100 80  
NAT Overload  
 
Router(config)# ip access-l stan lan_nat  
Router(config-std-acl)# permit ip 172.17.172.0 0.0.0.255  
Router(config)# ip nat source list lan_nat int fo/0 over

In order to check that translations and stats are Ok an working properly we can use the following commands:

show ip nat nvi translations  
show ip nat nvi statistics