DNAT (Destination NAT) is a type of NAT that allows inbound traffic to be redirected from a public IP address to a private IP address. DNAT is typically used when a server on a private network needs to be accessed from the internet. When a request is made to the public IP address, the NAT device will translate the public IP address to the private IP address of the server and forward the request to the server.

Use cases for DNAT:

Remote access: DNAT can be used to enable remote access to a server on a private network. For example, a company might use DNAT to allow employees to access a company server from home or when traveling.
Load balancing: DNAT can be used to distribute inbound traffic across multiple servers on a private network. This can help improve performance and ensure that traffic is handled efficiently.
Website hosting: DNAT can be used to host a website on a private network. When a request is made to the public IP address of the website, the DNAT device will redirect the traffic to the private IP address of the web server.

On the other hand, SNAT (Source NAT) is a type of NAT that changes the source IP address of outbound traffic. SNAT is typically used when multiple devices on a private network need to access the internet using a single public IP address. When a device on the private network sends a request to the internet, the NAT device will translate the private IP address to the public IP address before forwarding the request to the internet.

Use cases for SNAT:

Internet sharing: SNAT can be used to enable multiple devices on a private network to share a single public IP address. This is common in home networks where multiple devices (such as smartphones, tablets, and laptops) need to access the internet.
Security: SNAT can be used to hide the IP addresses of devices on a private network from the internet. This can help improve security by making it harder for attackers to target individual devices on the network.
Compliance: SNAT can be used to comply with certain regulations that require all outgoing traffic to have the same source IP address. For example, some financial institutions might use SNAT to comply with regulations that require all outgoing traffic to originate from a specific IP address.

Now that you have understood the differences between SNAT and DNAT, why don’t we go through a set of commands we can use to achieve this on Cisco equipment?

SNAT (Source NAT) and DNAT (Destination NAT) are two commonly used features in Cisco networking to manipulate network traffic. Here are the commands for configuring SNAT and DNAT in Cisco devices:

SNAT:

To configure SNAT on a Cisco router or firewall, use the following command:

ip nat inside source static  

This command tells the router/firewall to translate the source IP address of traffic leaving the “inside” interface to the specified “public” IP address.

DNAT:

To configure DNAT on a Cisco router or firewall, use the following command:

ip nat outside source static  

This command tells the router/firewall to translate the destination IP address of traffic arriving at the “outside” interface to the specified “local” IP address.

Note: The above commands are just examples, and the actual syntax may vary depending on the specific device and operating system version.

In summary, DNAT is used to translate inbound traffic to a private IP address, while SNAT is used to translate outbound traffic to a public IP address. Both DNAT and SNAT are useful techniques for managing IP addresses in a network and ensuring that devices on a private network can access the internet using a single public IP address.

I have another article demonstrating the real use case of NAT here – https://www.expertnetworkconsultant.com/configuring/how-to-configure-nat-the-cisco-and-vyos-way/

Here are some links to Cisco’s website that explain how to configure SNAT and DNAT:

SNAT:

Configuring Network Address Translation: https://www.cisco.com/c/en/us/support/docs/ip/network-address-translation-nat/26704-nat-faq-00.html

Configuring Static NAT: https://www.cisco.com/c/en/us/support/docs/ip/network-address-translation-nat/26704-nat-faq-00.html#anc13

DNAT:

Configuring Port Address Translation: https://www.cisco.com/c/en/us/support/docs/ip/network-address-translation-nat/26704-nat-faq-00.html#anc11

Configuring Dynamic NAT: https://www.cisco.com/c/en/us/support/docs/ip/network-address-translation-nat/26704-nat-faq-00.html#anc12

These links provide detailed information on the configuration of SNAT and DNAT, along with examples and best practices.