Cisco IOS Dynamic NAT Configuration

It’s time to configure dynamic NAT where we use a pool of IP addresses for translation. I’ll use a fairly simple topology with two hosts and 1 router that will perform NAT:

This time we have 2 host routers on the left side and I’m using another subnet. Let’s prepare the host routers:

Host1(config)#no ip routing
Host1(config)#default gateway 192.168.123.3

Host2(config)#no ip routing
Host2(config)#ip default-gateway 192.168.123.3

Next step is to configure NAT:

NAT(config)#interface fastEthernet 0/0
NAT(config-if)#ip nat inside 

NAT(config)#interface fastEthernet 1/0
NAT(config-if)#ip nat outside

First we’ll configure the correct inside and outside interfaces. Now I will create a pool with IP addresses that we can use for the translation:

NAT(config)#ip nat pool MYPOOL 192.168.23.10 192.168.23.20 prefix-length 24

The ip nat pool command lets us create a pool. I’m calling mine “MYPOOL” and I’m using IP address 192.168.23.10 up to 192.168.23.20. We can now select the hosts that we want to translate: