Public / Private network setup

January 26, 2007 at 09:46:25
Specs: Win Xp Pro, Celeron 2.8
I've been asked to expand an existing network and need advice or pointers to tech articles on the best way to set up a dual network.
The existing, working setup:-
Intelligent tills and telephone switchboard are connected to a couple of WinXPpro PCs via a basic newtwork switch. This equipment forms a fairly secure "back office" network separate from the "public" network. The public area has a public PC and wireless access point connected by the broadband router. In-between these networks, we have a PC with two network cards, one connected to the back-office network switch, and the second NIC connected via a hardware firewall to the broadband hub/router provided by the ISP. This PC is able to browse the back-office network and surf the net via broadband. So-far-so-good, this is the (undocumented) set-up I took over and it all works OK.

I now want to provide internet connectivity to another PC on the "back-office" network, I tried to imitate the setup of the working PC by fitting a second NIC card and a cable through to the firewall / BB router. Using this, the internet works OK so long as I disconnect the first NIC's patch cable to the "back-office" hub. Likewise I can only browse the "back-office" network while the second NIC patch cable to the BB firewall / router is unplugged (i also tried without the firewall but the same thing happened).

I suspect some sort of confict with DNS / DHCP services but can't find good quality info that applies, most articles are talking about windows internet connection sharing.

The set-up I inherited might not have been done the best way to start with. Any suggestions?

"Back-office" switch - NETGEAR FS605
"Firewall" Netgear FVS114 ProSafeā„¢
"Public Hub" British Telecom 1800HG Wireless Home Hub ADSL Router

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January 26, 2007 at 13:51:46
So the existing networks use one pc as a bridge between the public network and the backend right? Sounds like you are trying to accomplish this bridge twice with the second dual nic pc. What you need is a way to make the back office PCs talk to the Public hub, thru the bridging pc. To do this u need some software to run on the bridging pc that will send a wan IP to the backend pcs.
A simpler solution might be to just dispense with the pc's two nics and get a router/switch to act aas the network bridge. This means joining the PC which formerly had two nics to use one nic and join with the backend pcs on that network with the new router betweent he backend and the public network.

Compaq Presario SR1720NX Desktop Computer
AT&T SBC Yahoo DSL Home
Linksys Router/2 computers

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January 27, 2007 at 02:49:32
Thanks for the reply. The public network is already based around a BB router. I was not intending to use the first PC as a bridge (since it may not always be switched on). Instead I wanted to connect the second PC to the BB router so that both PCs would have an independant direct link to broadband. For security, I am trying to avoid linking the back office switch with the BB router. If I could draw a network diagram on here, it would be 2 stars side by side, with 5 nodes nodes each - 2 nodes on each star are my 2 PCs. I think what you are suggesting is to go for a single star (based around a new router/switch) with 10 nodes and to connect the BB hub as the 11th node. This would put my tills and public PC on the same network (worry).

I know that the 2 stars scenario works, so long as both PCs are not connected to both networks concurrently. To get it working, I think that all I need to do is alter the network setup on each pc so that it uses one NIC for Internet addresses, and the second for internal addresses (possibly also disable bridging on both PCs?). This is where my weak knowledge of XP Pro is letting me down.

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