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Re: expose internal network to the outside world

I agree with Sanchez. I run an old Pentium II as a NAT box with iptables and it gives me much more flexibility than a ("standalone") router. Routers dont need to be a cutting edge machine, old ones will do it just great for home networks. If you are not sure how to set up one, try reading the masquerade howto on the net.


On 9/14/05, Roberto C. Sanchez <roberto@familiasanchez.net> wrote:
On Wed, Sep 14, 2005 at 10:16:49PM -0400, Matt Price wrote:
> hi folks,
> I have 2 computers on a home network, connected to DSL through a modem
> and a cheap SMC router (Barricade  g = SMC2804WBRP-g).  I would like to
> be able to ssh into both of them form the outside world.  I have
> successfully set up "inadyn" to associate a stable URL (x.dyndns.org)
> with my dynamic IP, which is great.  Now the problem is to tunnel remote
> ssh requests to the two local machines.  I don't really understand this
> very well (though I tried something similar about 2 years ago -- got
> stumped then).
> As I understand it, what I need to do is set up some kind of a table
> where external requests on particular ports are forwarded by the router
> on to corresponding (perhaps not identical) ports on one or the other
> local machine.  SO I imagine something like this:
> from work, I type:
> ssh -p 2000 -l me mydomain.dyndns.org
> which gets to the router; the router sees that it's supposed to forward
> requests on port 2000 to; picks up the
> request and an ssh tunnel is formed
> on the other hand, if I type
> ssh -p 3000 -l metoo mydomain.dyndns.org
> the router sends the request to instead.
> On my router confiugration screen, there seem to be 3 places where this
> sort of thing can be done:
> 1. "DDNS" -- here I'm allowed to have 1 static IP address designated as
> a "server" ; requests on ports 80,21,and 25 (http, ftp, smtp) are
> forwarded on to the "server".  I've tried this and it works fine for
> http at least (I get the standard debian default index page from my
> local machine).  But there seems to be no further flexibility.
> 2. "NAT".  This section comes with the following instructions:
> *Special Applications*
> Some applications require multiple connections, such as Internet gaming,
> video conferencing, Internet telephony and others. These applications
> cannot work when Network Address Translation (NAT) is enabled. If you
> need to run applications that require multiple connections, specify the
> port normally associated with an application in the "Trigger Port"
> field, select the protocol type as TCP or UDP, then enter the public
> ports associated with the trigger port to open them for inbound traffic.
> Note: The range of the Trigger Ports is from 1 to 65535.
> THen there's a tablei nwhich I can associate "trigger ports" with
> "public ports".  But I odn't think I really understand what this is
> about, as thre seems to be no way to associate a particular local
> machine with a forwarded port.
> 3. DMZ.  THis screen lets me associate a local IP address ( 192.168.2.x)
> with a public IP address.  But this isn't what I want, is it?  Because
> after all I only have one constantly-changing IP address available to
> me...
> Anyway -- I feel a little bit stumped.  I wondered whether anyone else
> had ideas about what I should do, whether I'm out of luck, etc.
I use shorewall for my firewall, which lets me specify in simple rules
any ports I want forwarded and to which hosts they should be forwarded.
Other than that, I am sure you could whip up a short iptables script to
do what you want.


Roberto C. Sanchez

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