Cisco ASA Dynamic NAT with DMZ

In a previous lesson I explained how to configure dynamic NAT from the inside to the outside. In this lesson we add a DMZ and some more NAT translations. Here’s the topology that we will use:

In this example we have our INSIDE, OUTSIDE and DMZ interfaces. The security levels of these interfaces are:

• INSIDE: 100
• OUTSIDE: 0
• DMZ: 50

We can go from a “high” security level to a “low” security level so this means that hosts from the INSIDE can reach the DMZ and OUTSIDE. Hosts from the DMZ will also be able to reach the OUTSIDE. We will configure NAT for the following traffic patterns:

• Traffic from hosts on the INSIDE to the OUTSIDE, we’ll use a “public” pool for this.
• Traffic from hosts on the INSIDE to the DMZ, we’ll use a “DMZ” pool for this.
• Traffic from hosts on the DMZ to the OUTSIDE, we’ll use the same public pool for this.

Here’s what a visualization of these NAT rules look like:

Let’s start by configuring the interfaces:

ASA1(config)# interface e0/0
ASA1(config-if)# nameif INSIDE
ASA1(config-if)# ip address 192.168.1.254 255.255.255.0
ASA1(config-if)# no shutdown

ASA1(config)# interface e0/1
ASA1(config-if)# nameif OUTSIDE
ASA1(config-if)# ip address 192.168.2.254 255.255.255.0
ASA1(config-if)# no shutdown

ASA1(config)# int e0/2
ASA1(config-if)# nameif DMZ
ASA1(config-if)# security-level 50
ASA1(config-if)# ip address 192.168.3.254 255.255.255.0
ASA1(config-if)# no shutdown

The INSIDE and OUTSIDE security levels have a default value, the DMZ I configured to 50 myself. Now let’s look at the dynamic NAT configuration…

Dynamic NAT with three Interfaces

First we will create the pools:

ASA1(config)# object network PUBLIC_POOL
ASA1(config-network-object)# range 192.168.2.100 192.168.2.200

ASA1(config)# object network DMZ_POOL
ASA1(config-network-object)# range 192.168.3.100 192.168.3.200

I will use a range of IP addresses from the subnet that is configured on the OUTSIDE and DMZ interface. Now we can create some network objects for the NAT translations: