| ## ipfw/natd
## Dan Langille <>
Gateways: Installing natd/ipfw, firewall, dual-homed host
A gateway allows one computer to talk to an outside network and channel
requests from other computers. If you have more than one computer, it
makes sense to have one of them act as the gateway to your ISP. It allows
all of your computers to share a single modem. It's easy and it's cheap.
You don't want to do this if you are running ppp. See the man pages for
information on -alias.
One of the best ways to create a gateway is by using ipfw and natd.
ipfw is an Internet Packet Firewall. Even though you may not want a
firewall, it's the best way to achieve a gateway.
These instructions are taken directly from the
Please refer to that document for further information. This section assumes
that the network card which is attached to your ISP is ed0. You should
substitute your own interface if necessary.
1) You need FreeBSD version 2.2 or higher
Obtaining FreeBSD is not covered in this section. Please refer to the
section of the .
2) Build a custom kernel
I highly recommend you read Configuring the FreeBSD Kernel section of the
. Please pay
special attention to the Building and Installing a Custom Kernel section.
The rest of this section contains the highlights for those that know how to
build a kernel.
Include these options in your new kernel:
If this is the first time you've created a new kernel, you may wish to
reboot and install that new kernel. Make sure your kernel reboots safely
with no error messages. If all you have done is the above changes, it
should go very smoothly.
3) Create a gateway/firewall
Ensure your machine acts as a gateway and a firewall by including the
following lines in /etc/rc.conf:
4) Configure your interface
Make sure your network cards are already configured. Sorry, but I
don't cover that here. If you're using ppp, make sure you start ppp
before running natd.
5) Add natd to your services
Ensure the following line appears in /etc/services:
natd 8668/divert # Network Address Translation socket
6) Start natd
This can be added to /etc/rc.local:
natd -interface ed0
7) Redirect the traffic to natd
You will need at least the following commands:
/sbin/ipfw -f flush
/sbin/ipfw add divert natd all from any to any via ed0
/sbin/ipfw add pass all from any to any
See for more information.
In order for the changes you've made to take effect, you'll need to
reboot. Things should run smoothly now.
If it doesn't work
If the above does not get things working for you, then
. Perhaps my
instructions are defective. I don't think so, but please tell me of any
problems you had and what you did to correct them.
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