Cisco ASA double NAT with DNS translation

Cisco ASA Double NAT with DNS Translation

Network Address Translation (NAT) is a network security feature that is used to translate a public or private IP address to another public or private IP address. It is commonly used to hide private IP addresses from public view, which helps to protect a network from outside intruders. However, it can also be used to provide access to internal networks from the Internet. Double NAT is a configuration where two NAT devices are used in a network.

The Cisco ASA firewall is a popular and powerful security device that can be used to perform a variety of network functions, including NAT. In some scenarios, it may be necessary to configure a Cisco ASA firewall with two NAT devices. In this article, we’ll discuss how to configure a Cisco ASA firewall with double NAT and DNS translation.

The most common scenario for a double NAT setup is when two ISPs (Internet Service Providers) have provided Internet access to a network. In this situation, it’s often necessary to configure two NAT rules on the ASA firewall. The first NAT rule will be used to translate the public IP address of the first ISP to the private IP address of the internal network. The second NAT rule will be used to translate the public IP address of the second ISP to the same private IP address of the internal network. This setup allows both ISPs to provide access to the internal network from the Internet.

In addition to the two NAT rules, you will also need to configure a DNS translation rule on the ASA firewall. This rule will allow the ASA to translate the public IP address of the second ISP to the private IP address of the internal network. This is necessary in order for the internal network to be able to access the Internet.

When configuring the double NAT setup on the ASA firewall, it’s important to ensure that the internal network is using the same private IP address. If the internal network is using a different private IP address, the ASA will not be able to properly route the traffic between the two ISPs.

In addition to the double NAT and DNS translation rules, the ASA firewall must also be configured with static routes. These routes will be used to ensure that the traffic is properly routed between the two ISPs. It’s also important to ensure that the ASA is using the correct NAT rules for the traffic that is being sent and received.

Finally, the ASA firewall must be configured to use the appropriate security policies. This will ensure that the traffic is properly filtered and that the internal network is protected from external threats.

Overall, configuring a Cisco ASA firewall with double NAT and DNS translation is a fairly straightforward process. However, it is important to ensure that the configuration is done correctly in order to ensure that the network is safe and secure. Additionally, it’s important to ensure that the internal network is using the same private IP address in order for the double NAT setup to work properly. Once the ASA is properly configured, it should provide the necessary protection for the internal network from external threats.