Книга: Iptables Tutorial 1.2.2

The final stage of our NAT machine

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The final stage of our NAT machine

As a final step, we should bring all of this information together, and see how we would solve the NAT machine then. Let's take a look at a picture of the networks and how it looks. We have decided to put a proxy just outside the NAT/filtering machine as described above, but inside counting from the router. This area could be counted upon as an DMZ in a sense, with the NAT/filter machine being a router between the DMZ and the two company networks. You can see the exact layout we are discussing in the image below.


All the normal traffic from the NAT'ed networks will be sent through the DMZ directly to the router, which will send the traffic on out to the internet. Except, yes, you guessed it, webtraffic which is instead marked inside the netfilter part of the NAT machine, and then routed based on the mark and to the proxy machine. Let's take a look at what I am talking about. Say a http packet is seen by the NAT machine. The mangle table can then be used to mark the packet with a netfilter mark (also known as nfmark). Even later when we should route the packets to our router, we will be able to check for the nfmark within the routing tables, and based on this mark, we can choose to route the http packets to the proxy server. The proxy server will then do it's work on the packets. We will touch these subjects to some extent later on in the document, even though much of the routing based part is happening inside the advanced routing topics.

The NAT machine has a public IP available over the internet, as well as the router and any other machines that may be available on the Internet. All of the machines inside the NAT'ed networks will be using private IP's, hence saving both a lot of cash, and the Internet address space.

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