How to configure separate networks for SBS and Win2k Servers

How do I configure separate networks for a windows Small Business Server 2003 server and a Win2k Server. We have two organizations that are currently sharing a Win2k server that is attached to a Cisco 1721 router and an HP 4100 switch . We have a T1 line with dedicated Internet services. We have 13 IP addresses but we only use one IP Address.

Because of changes in the business we have put the the organizations on separate servers but we want to continue to share the Internet Connection. We have purchased a new SBS Server Machine with two NIC Cards for one of the organizations. We plan to leave the other orgranization on the existing Win2k Server.

What do we have to do to separate the two networks but still share the ISP services? For legal reasons I cannot route traffic through the same server. . . . .
Who is Participating?
Its easy. Here is how you can do it.

Old Network:
New Network:

                                                /Network 1
Internet Router---------Switch/-----------------------------SBS-------------------------Network 2
                                                           External IP             Internal IP

For network-2  SBS internal IP would be Default Gateway and DNS server.

For SBS itself, router would be the default gateway.
Do not put default gateway on internal NIC on SBS.
Also, on SBS box, do no specify ISPs DNS in any of the network cards.
Instead use Forwarders in the DNS server.

One more thing, Goto the properties of the External NIC.
Choose TCP/IP and click properties button.
On General Tab,Click Advanced.
Then on new windows, Click on DNS tab.
Here in bottom, uncheck "Register this connections address in DNS".

This has to be done for external NIC only.

It will prevent your network for having two entries for your domain.

SBS would Run either ISA or RRAS for internet access.


Internet - Switch -- Router -- oldWin2k - Network
                  ------- Router - newWin2k - Network

What about something like the above?
The 1721 supports multiple eth modules so you could seperate the traffic behind the router. Best if you only want to manage one router.

Internet - Router -- switch 1 -- oldWin2k - Network
                   ------- switch 2 -- newWin2k - Network

An alternative is to seperate the traffic on a managed switch behind the router. Best if you don't want to buy another switch.

Internet - Router -- switch -- VLAN 1 -- oldWin2k - Network
                                 ------- VLAN 2 -- newWin2k - Network

It largely depends on whether you need seperate services for both networks exposed to the outside. Such as email and web servers.
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The easy way to seperate the networks is to give a different range of IP Addresses to each network.

Network1 - 192.168.0.x
Network2 - 192.168.1.x

Then set the router as the default gateway on each network.

Make sure you dont create a router between the two networks and that way they wont be able to interact.

Of course this approach means the router must have two NIC's or if its Cisco you can create a virtual networks on the one port.
> Make sure you dont create a router between the two networks and that way they wont be able to interact.

Should be
> create a static or dynamic route between the two networks
xpressaccountsAuthor Commented:
Thank all you guys for the suggestions. I'm a novice when it comes to networks so please excuse if my questions lack understanding of what you are suggesting I do. I'm still a little foggy but this dialog has helped.

First let share some more background. My current Win2k server and LAN uses static ip addresses and it is configured as Workgroup not a Domain. What I want to do is take about 12 of my users and put them on the new SBS 2003 Server, leaving the rest of my users on the win2k server and LAN.

Here are the current Windows XP PC Configurations:
Default Gateway for PC's:
Static IP Address for PC's to each PC)
Server IP -

WAN/ Router IP Addresses from SBCIS:
Available IP's -
Router Lan Interface Address -
SBCIS WAN Interface Serial Address -
Customer WAN Interface Address
What are the specific changes I have to make to my router? if any? What are the specific changes I need to make to the switch? if any? What changes do I need to make to the server? Old or New?

Thanks I appreciate the help.
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