Source Nat VS Destination Nat | Key Differences

Source Nat VS Destination Nat | Key Differences 

Network Address Translation or Nat is a method by which Ip Address information is modified in IP packet headers while it is in transit across a traffic routing device. It is used to gain access with an internal or external network to an external or internal network and having control over the network access. That being said, what are Source NAT and Destination NAT? What are their functions?

Source NAT and Destination NAT are two different types of NAT. Source NAT translates the IP address coming from a secured private network when it connects to the internet. Destination NAT translates the IP address of a public host as it enters the router of a secured network.

Source Network Address Translation (SNAT) and Destination Network Access Translation (DNAT) are two types of Nats based on translation mode. Both of these Nats are unique and have their differences. The usage also varies for both these depending on what Ip addresses are being translated. Both types of network address translations are going to be discussed and compared for better understanding.

What Is Source NAT?

Source Network Access Translation otherwise known as SNAT is the process of translating the source’s private IP address into a public IP address to connect to the internet. As the name suggests, the whole process is about translating the source IP address. It is mostly used by private users for getting public access such as the internet. SNAT might also change the source port present in the TCP/UDP headers.

It is how a user bypasses the firewall inside a LAN to get connected to the internet. It keeps changing the source IP packets continuously through the NAT device. It only operates after a user chooses to get connected to the internet. So if the user is not connected to the internet, SNAT is not activated. SNAT is only activated when the user is inside a secured network and is looking to make the connection to the internet. The source IP is then translated for access.

SNAT is also operated when multiple hosts are trying to get access to any public host outside. All this process keeps the source NAT private and protected. Source NAT can be divided into 3 types. They are given below:

Dynamic IP And Port (DIPP) 

Dynamic IP And Port is otherwise known as DIPP is the process by which multiple hosts translate their source IP addresses to the same public IP address by assigning port numbers to each user. Instead of generating multiple IP addresses, it chooses to use the same IP address with different port numbers. By this, a lot of users are allowed to connect to the internet by the same routing device. By doing this DIPP allows the user to specify the address of the interface locally. This is why it is also known as Interface-Based NAT or Network Address Port Translation (NAPT).

Dynamic IP 

Dynamic IP, unlike the DIPP, allows one-to-one translation of source IP addresses only. This means there is no port number and the dynamic translation of source IP is only to the next available address that can be found in the NAT address pool. It requires an equal number of NAT pool size to the number of internal hosts for address translation.

Static IP 

In static IP, 1-to-1 static translation of source IP is done but it doesn’t change the source port. For this, an internal server must be available to the internet for a static IP translation.

What Is Destination NAT?

Destination Network Access Translation otherwise known as DNAT is a process where the destination address is changed in the IP header of a packet. Unlike the Source NAT, Destination NAT deals with the IP address of the public access or internet. It changes the IP address from the destination as it passes through a router. It can also change the port translation in the TCP/UDP headers. It is used to redirect traffic from an internet host to a private host.

Destination NAT’s main job is to redirect the IP address packets that are being received from an external source to an internal source or network. It only allows connections for network connections that are incoming to the private network. It translates a single IP address to a different IP address to bypass a private network firewall. It translates the destination IP and Port to a different one for access. It also translates blocks of addresses of the same size.

Destination NAT is used by the websites that are on the internet which needs to allow access to the private networks for usage. For that, it changes the destination when it passes through the router. Destination NAT is performed before the user chooses to get connected to the website. Thus it can give you access to the information. It establishes the connection of an unsecured network to the secured network that the users are inside.

Key Differences Between Source NAT And Destination NAT

The key differences between the Source NAT and Destination NAT are given below:


Source NAT performs inside a secured network while Destination NAT is performed outside a secured network.


Source NAT is used by a client that is inside a secured network to get access to the internet. Destination NAT is used by a website to give access to the users behind a secured network.

Number Of Hosts 

Source NAT allows multiple private hosts inside the same network to make connections to an outside host. Destination NAT allows any hosts outside a secured network to make connections to one inside host.


Source NAT is used to translate the user IP inside a private network to gain access to the internet. While Destination NAT is used to translate the IP of a public host before it enters a secured private network.

Address Translation

Source NAT translates the address of the source IP. Destination NAT changes the address of the Destination IP.

Order of Access 

Source NAT is activated after the user decides to perform routing. While Destination NAT is activated before the user decides to perform routing.

Connection Target 

Source NAT’s targeted access is to the public hosts or internet from a secured network. Destination NAT’s targeted access is the private hosts inside a secured network from an unsecured network.

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