Port forwarding behind two routers

Luke Dean LukeD at pobox.com
Sat Nov 15 10:42:46 PST 2008

On Sat, 15 Nov 2008, Jakub T wrote:

> Good day people,
> I'm trying to get wireless Internet access for my laptop and to use this
> wireless router as a switch  for my FreeBSD box at the same time. This
> wireless router has one Internet plug and for Ethernet plugs for wired
> boxes. Now I have this situation:
>        |
> telephone/adsl-wire
>        |
>        |
>    ADSL router
> wan : xx.xx.xx.xx                          FreeBSD box (wired)
> lan :                          ip:
>        |                 laptop            gateway:
>        |                 (wireless)                |
>   [internet plug]        ip:         |
>  Wireless router         gateway:      |
>  lan :  . . . . . :                    |
>   [ethernet plug]                                  |
>        |                                           |
>        +-------------------------------------------+
> The wireless router software configured the router like this:
> Destination     LAN IP Subnet   Mask Gateway    Interface
>     WAN (Internet)
>     LAN & Wireless
>     WAN (Internet)
> ... so it works as a switch for two boxes and as a router at the same time.
> The FreeBSD box is configured like this:
> ifconfig_XXX0="inet netmask"
> defaultrouter=""
> Now I have Internet connection on both computers. However, I can't get aMule
> and other apps that need port forwarding working on FreeBSD box.
> First, I tried to configure ADSL router ( just to forward 4662
> port to, doesn't work.
> Then, I tried this:
> router: forward 4662 to
> router: forward 4662 to
> not working again.
> I have a feeling that I'm missing something very simple, but can't figure
> out what.
> (A note: before I acquired a wireless router, forwarding with one router was
> just working, with FreeBSD box configured as, so that side of
> things is ok. And, no, it's not possible to use just wireless router because
> I can't plug telephone wire in it.)
> Can anyone help me? Should I post more details? TIA,
> Jakub

Port-forwarding through two NATs is something I've never had any success 
with.  I have a few suggestions that have worked for me and my 
friends with this setup.

A) Disable NAT on the ADSL router.  I think the term is "bridged mode". 
Turn it into a dumb box and shift all the NAT/firewall/routing 
responsibilities over to your wireless router.  Depending on your ISP, the 
hardware, and the protocols involved, this may not be an option for you.

B) Disable NAT on the wireless router.  This allows it to be a simple 
switch and wireless access point.  The price is that you're probably 
relying on the DHCP server in the wireless router for your wireless 
devices and you'll have to disable the DHCP when you disable NAT.  This 
creates new problems to be solved.

C) Plug the FreeBSD box into the ADSL router, skipping the wireless 
router.  Your wireless devices will still be double-NATted, but if you're 
not running servers on them, you might be able to live with that.

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