> -----Original Message-----
> Hello,
>      I am looking to replace a proprietary DSL router/modem
> with the Sangoma S518 ADSL PCI Controller, thereby placing a
> FreeBSD (4.10-Stable) server running ipfw to handle access,
> firewall and nat duties.
> The ISP's DSL package includes 8 static ip addresses: -
> 1 - network addr
> 1 - broadcast addr
> 1 "router" address
> 5 usable ip addresses
> I have been reading up on NAT and address redirection in the
> HandBook
> (http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/net
work-natd.html) and have come accross section 19.13.5 Address
Redirection. Here it reads:

The -redirect_address syntax is as follows:
-redirect_address localIP publicIP
localIP         The internal IP address of the LAN client.
publicIP        The external IP address corresponding to the LAN client.

In the example, this argument would read:

What I would like to know is if it is possible to do to following: -
Given that the 5 usable public IP's are:,,, & 1] G'Way host is assigned its own public IP -
2] LAN hosts' (all) traffic is NAT'd using one of the other public IP's
- 3] Remaining 4 public IP addresses are left to be used other
purposes (eg: "true" address redirection to a DMZ-host, that is not a
member of the internal LAN subnet)

As you see, the g'way's public ip is not being used for NAT'ing internal
hosts' outgoing traffic, but another ip from within the assignied public
ip address range. My reading of the NAT chapter does not suggest that
there is a way to define the public IP with which traffic is to be
translate. Is this functionality not supported, or have I missed
something when reading the various sections?

I'd appreciate any pointers to where I might find more information that
might assist me, or an explanation of what it is that I am not
understanding when reading the HandBook.


The public IP address for the gateway WILL be used for NAT'ing, if you
choose to do so.  In order to get things to work correctly, you're going
to need three NICs installed in this machine (counting one of them as
the DSL PCI card).  Their use are as follows:

Sis0: This is your DSL interface (probably not going to be called sis0)
Sis1: This is your internal, non-DMZ interface, i.e. NAT'd.
Sis2: This is your DMZ interface, i.e. non-NAT'd.

If you read the man pages on NAT (man nat, iirc), you'll learn the
syntax and such to use within your rc.conf file to configure the correct

When I've got more time, if you can't figure it out, I'll post a more
elaborate configuration for you.


Eric F Crist
AdTech Integrated Systems, Inc
(612) 998-3588

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