Mail Servers and VPN for two Networks

I currently have a fully functional SBS 2003 network running ISA 2004 as proxy, VPN access, OWA, Hosted Websites, Intranet and SharePoint Services.
I am in the process of setting up a R&D network with Mail Server and web server which is entirely Linux based to run similar services but on a difference network address. This is simple to achieve if I install a separate DSL line with static IP for the R&D network to access the Internet.
My question is can these services be achieved on the Linux network without the introduction of a second Internet connection and without disturbing the services on the current SBS Network? If so what devices or configuration is required?  Please advise on options – Thank you.
Compuit1Asked:
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chakkoCommented:
Do you have 2 Public IP addresses (or more) on your current Internet connection?
If you need the Linux stuff to use standard ports (eg SMTP 25) then you will need a different IP address for those services, either get an Internet package with additional IP's or you need another Internet connection
Then for your equipment, it depends on what capabilities/features you have.
I would create another network (or VLAN) for the Linux and in your router setup the new extra Network and routing.
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chakkoCommented:
You could also use your ISA to connect the networks, but if this is for R&D it may be better to not do that so you don't complicate your ISA configuration.

I would something like this

Internet
   |
Router   ---    ISA/LAN
   |
Network for Linux
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Compuit1Author Commented:
Yes the configuration you show is exactly what I have setup. So the problem with two networks – Let’s say mail servers listening on port 25 will fail. Can it be redirected using FQDN? I do not think the SMC Router used in the DMZ can redirect as required. I know having a separate public address for each network will be the solution but before going down that channel I want to be certain. Can you confirm please?
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Compuit1Author Commented:
Just wondering if some like this could be done:

Internet
      |
 Router
      |
DMZ Multi NIC device (Windows or Linux routing)
      |    192.168.10.XXX                             |      192.168.20.xxx
ISA 2004                                                Linux Mail - R&D Network abc@bbb.co.nz
SBS 2003 Exch Mail abc@aaa.co.nz            
192.168.45.xxx
Production Network      
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chakkoCommented:
with only 1 IP address I don't think it's going to work.  I don't know of any router that can forward SMTP protocol on some rule basis such as FQDN.

Not sure of your requirements exactly, but you could change the Linux SMTP listening port to something like TCP 26.  Then route the mail that way.  If you need inbound email you could buy a hosted email filtering/AV/Spam service and have them as the MX record then they would forward mail to your linux box on port 26

If you only need SMTP service on the internet side then I have an idea to setup a Mail Gateway type of box for incoming SMTP.  It would receive the mail for both domains an then do a domain level forwarding to either Exchange or Linux.  But it would have to be the email gateway system in front of your Exchange.

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Compuit1Author Commented:
OK Chakko - Thank you - You have confirmed my thoughts I will wait a little longer to see if there is another opinion - Then close and assign the points - Thank you.
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Compuit1Author Commented:
Right no further input. I accept your advice - Thank you.
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