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From: "Lawrence Farr" <freebsd-isp@epcdirect.co.uk>
To: "'Aled Treharne'" <aled@thinknuts.org>, <freebsd-pf@freebsd.org>
Date: Mon, 25 Oct 2004 16:59:44 +0100
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Subject: RE: NAT with IP != primary external IP
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> -----Original Message-----
> From: owner-freebsd-pf@freebsd.org 
> [mailto:owner-freebsd-pf@freebsd.org] On Behalf Of Aled Treharne
> Sent: 23 October 2004 12:15
> To: freebsd-pf@freebsd.org
> Subject: NAT with IP != primary external IP
> 
> Hi guys.
> 
> I'm trying to set up a firewall on a box for a friend. The 
> arrangement is
> fairly simple, bunch of machines behind the FBSD box, FBSD 
> box connected to
> ADSL. What I'd like to do (because I wanted to in the first 
> place, and now
> it's annoying me) is to have 2 Ips on the external i/f on the 
> FBSD box, and
> have one as the machine's primary IP and t'other solely as 
> the NAT IP. I've
> tried putting various Ips in the places that make sense to 
> me, but I just
> couldn't get it to work[1].
> 
> Is this possible, and if so, would someone be so kind as to 
> tell me how? I'm
> trying to move over to pf from ipfw, and if I can get it 
> working, I've got a
> strong case for using it at work as well. 
> 
> Thanks in advance for your sage advice. :)
> 
> Cheers,
> Aled.
> 
> [1] This is just one place where I prefer linux's eth0:alias1 
> type labelling
> of sub-interfaces over FreeBSD's 
> just-put-multiple-ips-on-one-interface way.

I use the following:

ext_ipa="1.2.3.4"
axt_ipb="1.2.3.5"
net_if="fxp0"
table <inets> { 7.8.9.0/24, 4.5.6.0/24 }

nat on $net_if from <inets> to any -> $ext_ipb

So traffic matching <inets> gets sent out via $ext_ipb,
all other traffic comes out on $ext_ipa. 

Regards,

Lawrence Farr