These are Instructions for Configuring A FreeBSD Box For NAT 
After you have installed IpFilter.

You will need to change three files:

/etc/rc.local
/etc/rc.conf
/etc/natrules

You will have to:

1) Load the kernel module
2) Make the ipnat rules
3) Load the ipnat rules
4) Enable routing between interfaces
5) Add static routes for the subnet ranges
6) Configure your network interfaces
7) reboot the computer for the changes to take effect.

The FAQ was written by Chris Coleman <chris@@bbcc.ctc.edu>
This was tested using ipfilter 3.1.4 and FreeBSD 2.1.6-RELEASE
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1) Loading the Kernel Module

If you are using a Kernal Loadable Module you need to edit your
/etc/rc.local file and load the module at boot time.
use the line:

        modload /lkm/if_ipl.o

If you are not loading a kernel module, skip this step.
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2) Setting up the NAT Rules

Make a file called /etc/natrules
put in the rules that you need for your system.

If you want to use the whole 10 Network. Try:

map fpx0 10.0.0.0/8 -> 208.8.0.1/32 portmap tcp/udp 10000:65000

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Here is an explaination of each part of the command:

map starts the command.

fpx0 is the interface with the real internet address.

10.0.0.0 is the subnet you want to use.

/8 is the subnet mask.  ie 255.0.0.0

208.8.0.1 is the real ip address that you use.

/32 is the subnet mask 255.255.255.255, ie only use this ip address.

portmap tcp/udp 10000:65000 
        tells it to use the ports to redirect the tcp/udp calls through


The one line should work for the whole network.
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3) Loading the NAT Rules:

The NAT Rules will need to be loaded every time the computer
reboots.

In your /etc/rc.local put the line:

ipnat -f /etc/natrules 

To check and see if it is loaded, as root type
    ipnat -ls
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4) Enable Routing between interfaces.

Tell the kernel to route these addresses.

in the rc.local file put the line:

sysctl -w net.inet.ip.forwarding=1

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5) Static Routes to Subnet Ranges

Now you have to add a static routes for the subnet ranges.
Edit your /etc/sysconfig to add them at bootup.

static_routes="foo"
route_foo="10.0.0.0 -netmask 0xf0000000 -interface 10.0.0.1"


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6) Make sure that you have your interfaces configured.

I have two Intel Ether Express Pro B cards.
One is on 208.8.0.1 The other is on 10.0.0.1

You need to configure these in the /etc/sysconfig

network_interfaces="fxp0 fxp1"
ifconfig_fxp0="inet 208.8.0.1 netmask 255.255.255.0"
ifconfig_fxp1="inet 10.0.0.1 netmask 255.0.0.0"
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