Linux 2.4 NAT HOWTO: The Two Types of NAT

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## 3. The Two Types of NAT

I divide NAT into two different types: Source NAT (SNAT) and Destination NAT (DNAT).

Source NAT is when you alter the source address of the first packet: ie. you are changing where the connection is coming from. Source NAT is always done post-routing, just before the packet goes out onto the wire. Masquerading is a specialized form of SNAT.

Destination NAT is when you alter the destination address of the first packet: ie. you are changing where the connection is going to. Destination NAT is always done pre-routing, when the packet first comes off the wire. Port forwarding, load sharing, and transparent proxying are all forms of DNAT.

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