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Re: ADSL, routers firewalls etc.

On Mon, 2002-10-14 at 21:29, Tom wrote:
> I have already purchased a Hub for the network which consists of a Debian
> MySql and Apache server, another Debian firewall box and some Win boxes.
> My confusion lies in both terminology and setup.  I imagined before starting
> that I would need to set up a firewall machine with 2 network devices.  The
> firewall would then manage security and masquerading, where the external eth
> device will be allocated the static IP  (Non-NAT) I have been given by my
> ISP.
> However research of the most common Ethernet DSL modems (cheapest about $100
>  / £ 66) suggests that
> 1) the modem has NAT, firewall etc all built in.
> 2) many manufacturers combine a network hub and modem.
> 3) the modem itself must be assigned an IP not the machine it is fixed to????
> I'm assuming therefore that the firewall machine is not required.  I had
> previously thought that a gateway machine such as a firewall was necessary
> for me to be able to SSH to do remote admin.
> Also I have already purchased a hub and the firewall machine (old box
>  knocking around) therefore I was hoping to just get a modem.  I do not have
>  USB.
> Any comments welcome, and thanks in advance for reading this far!

It all depends on how your ISP configures your DSL. There are two ways
that ADSL ethernet modems operate. One is PPPoE (PPP over Ethernet) and
the other is Bridged. 

I always have a gateway with two Network cards. One will attach to the
DSL modem via cat5, the other connects to your inside network (your
hub/switch). This requires buying a DSL modem and a switch/hub (which
you already have).

If your ISP uses bridged mode then you'll assign the external ethernet
cad your allocated IP address/netmask/gateway etc. 

If your ISP uses PPPoE (by far the most common) then you wont configure
the external network card at all, and you will run a pppoe connection
that will be assigned your IP etc via a PPP connection over the ethernet

In both cases the modem is not assigned an IP. In PPPoE, neither is the
Ethernet card. If the modem were assigned an IP (or two, one for each
interface) it would be called a router (you can get DSL routers).

Kind Regards
Crispin Wellington

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