I apologise in advance for this, but I think that I have just gotten myself confused and would appreciate someone helping me to see the forest instead of the trees again.

I am setting up a home-based LAN connecting to the Net via an ADSL modem which in turn is connected to a firewall/router which in turn will be running a web server on a DMZ branch and a 3 machine LAN on the second branch. The firewall has 3 NICs and works as follows (I tried an ASCII diagram but that didn't work on the preview):

the LAN has 3 machines (box1, box2, box3) and connects to firewall via a switch to eth0;
the DMZ has 1 machine and connects to the firewall via a switch to eth1; and
the ADSL ethernet modem connects to the Internet and to firewall NIC (eth2) (running PPPoA because it is a UK ADSL provider)


IP Addresses:
box1 = IP 10.0.0.20
box2 = IP 10.0.0.40
box3 = IP 10.0.0.20
DMZ = IP 10.254.0.20
switchA -> firewall = IP 10.0.0.1
switchB -> firewall = IP 10.254.0.1

question:
Given the foregoing, my question comes down to this:
on the NIC that connects to the ethernet modem, do I assign the IP address and if so, what would that be, or is this automatically assigned by virtue of the ADSL ISP at boot up?
I do know that the ISP does not provide a static IP address, but I am not clear on whether or not this means that the IP address on the modem-facing NIC will be dynamically assigned as a consequence.

It could be the way I am asking this question, but Google provides loads of details that is unfortunately adding to my confusion, so if someone could help clear the fog, I'd be very appreciative.

TIA

Hi,

not sure if I can help you with this as I am not a networking expert but a few words that may/maynot be of help.

1. I would think the isp should provide the ip for the nic connected to the modem, since if there was only one machine (nic) on the network the ip address would be provided by the isp.

2. There may be a reason for this but should box1 and box3 have the same ip address? I have seen cases where if 2 machines/nics on the same network have the same ip address the router has no clue of what is going on and will simply leave those machines off the network.

it appears you do have a bit of complex setup which is hard to follow, what are the ip's of the nics on the firewall? Sorry I couldn't be of more help, I hope my suggestions help.

You modem will assign an IP to eth2 because it's your WAN port on you firewall/router.

the DMZ has 1 machine and connects to the firewall via a switch to eth1
Why are you using a switch for one machine? Doesn't make sense to me? Wouldn't it just be a cross over cat 3 cable?

Why does box1 and box2 have the same IP? Is that a typo?

Hey thanks chbin and schootdog for your responses. You are also quite correct - I made a typo for box 3. The correct IP for that box is actually 10.0.0.60 ... sorry I am using a switch on my DMZ so that at some point, if I want to I can add to it. Also, it doesn't lower performance any (afaik). Yep, a crossover could've worked just as well it is true, but oh well. Just a design decision basically, with an opportunity to expand should I wish at some point in the future.

After doing (yet) more reading, the dynamically assigned IP address would indeed be assigned to the NIC facing the modem/Internet so your responses and further digging around have confirmed what I suspected but wasn't certain about.

Many thanks people.