ADSL modem & ip addresses

[Luke Kearney]

On Fri, 10 Oct 2003 11:41:01 -0400
"liquid" <liquid at homebass.ca> granted us these pearls of wisdom:

> 
> 
> > -----Original Message-----
> > From: owner-freebsd-questions at freebsd.org [mailto:owner-freebsd-
> > questions at freebsd.org] On Behalf Of Ian Moore
> > Sent: October 10, 2003 9:59 AM
> > To: freebsd-questions
> > Subject: ADSL modem & ip addresses
> > 
> > Hi,
> > I'm organising an ADSL connection and I'm a bit confused about our
> > options.
> > 
> > We need to provide web, ssh and mail access to our network for users
> > from home
> > across the Internet with an ADSL connection.
> > I figure the best way to do this is to setup a new machine to act as a
> > firewall and run a web server & sendmail on this box. (or I have seen
> > something about using socket to divert these services to our existing
> > server
> > which has a private address).
> 
> It's not a wise move to run the services on the same machine as your
> firewall.  You can setup an openbsd machine to serve as your firewall on
> a very inexpensive old machine, running it as a gateway as well.  You
> can then forward specific ports (80, 25, 110 in your case) to your
> services machine running either in a DMZ or behind the firewall.
> Regarding the whole diverting issue, I encourage you to google "dual
> homed hosts"  I had some pretty favourites on my windows machine but I
> lost them all when a hard drive died or I'd have some good ones for you.
> 
> > The firewall would have a NIC with a private IP address to connect to
> > the rest
> > of our network.
> > 
> > What's the best way then to connect it to the ADSL line?
> > Do we have a second NIC in the firewall machine with a real IP address
> > connected to an ADSL modem and use ppp -natd on that interface? Does
> > that
> > mean we'd need 2 static IP addresses - one for the firewall & one for
> > the
> > modem? (We really don't want to pay for 2 addresses)
> 
> If you use pppoe, you can run ppp -ddial -quiet on startup by including
> that in rc.conf.  Checkout /etc/defaults/rc.conf.  I setup a machine to
> act as a gateway/firewall for 5 PC's on a 3mbit dsl line once... on a
> P120 and it ran flawlessly.
> 
> You don't need two IP's.  Your modem *shouldn't* have to have an IP.  If
> it does, it's because it also acts as a router and hence does the pppoe
> auth.  I suppose you can use that as a router instead.. it's your
> network ;)  I like the flexibility my router provides me however.  It's
> remarkably easy to setup as well.  Again I don't have any links right
> now off-hand, but if you search for pppoe + freebsd + ipnat or something
> you'll find some very good tutorials.  There was this one for a cable
> connection I used as a guide the first time, and just followed the steps
> from other sources for setting up PPPoE.
> > 
> > Or can we use a USB connection instead - are there FBSD drivers for
> > ADSL
> > modems? I can't see any in the supported hardware list.
> 
> AFAIK, there is no support (yet?) for a usb modem.  I don't like them
> anyway - I keep my apples with my apples, my oranges with... you guessed
> it, the oranges.  ADSL = network related stuff = runs on Ethernet.
> > 
> > Or do we use a combined modem/router device to do the nat &
> > firewalling and
> > have it redirect mail, web & ssh access to our main server? (is that
> > possible
> > or do such devices not allow access into the network from the 'net?)
> > 
> by default they will not.  As I said they work, but I'm not sure the
> devices that are a modem + router built-in will also include
> firewalling.

Actually quite a few of the SOHO DSL routers I've seen do include simple
firewalling but often enough they are only configurable via a browser
and have a kind of all or nothing stance. For fine granular control over
the firewall it is hard to beat FBSD and IPFilter / IPFW for the price -
it just doesn't come with a pretty web interface ( not that you couldn't
build one if you had the time or the energy I suppose.