Connecting to two Ethernet networks simultaneously


Thread Starter


The IT guys have configured my PC (NT4.0) to connect to the 'office' LAN using their domain and DHCP. The SCADAs on the 'control' LAN are configured (NT4.0) as a workgroup with static IPs. I've got both networks at my desk. Can my PC be configured to login to the 'office' LAN and still have access to the 'control' LAN (SCADAs and PLCs) at the same time? Is there a problem with the Domain/Workgroup difference? Thanks in advance.

Hunter Farris

Get a static IP address from your IT guys. Then configure the subnet mask so that it will access the addresses on the SCADA network based on subnet assignment.

David Wooden Omron

>Can my PC be configured to login to the 'office' LAN and still have
>access to the 'control' LAN (SCADAs and PLCs) at the same time? Is there
>a problem with the Domain/Workgroup difference?

I'm currently using a PC with 2 network cards, one DHCP and one using static IP addresses. Use the latest service pack(6) so that changing the IP
address will not force you to restart Windows. Not sure on the workgroups as our control network mostly uses TCP/IP directly, but TCP/IP addresses
resolve themselves to the proper network. If you ping on an address which maps to the network that one or the other card is on, the proper card will
be accessed.


David Wooden
Senior Software Engineer, Systems Integration
Automation and Enterprise Solutions Group
TAS Division of Omron Electronics LLC
Office: (847) 884-7034 Extension 432
Fax: (847) 884-9383
E-mail: [email protected]

Robert Dusza


You can modify the host file in the winnt\system32\drivers\etc directory. Just follow the instructions. With the SCADA PCs using static IP addresses, you will be able to see them form this network as well as from any other system (if there is a connection to yours). We have a WAN here that encompasses 12 VLANs and I am able to see both of the SCADA systems ( Water and Wastewater) without any problems. This includes through our dial-up server.

With this setup you don't have to use two networks cards on your PC.

Any questions, let me know.


Robert J. Dusza, Jr.
Treatment Manager
(V) 1-860-647-3219
(F) 1-860-647-3150
E-mail - [email protected]
Manchester Water & Sewer Dept.
125 Spring St. P.O. Box 191
Manchester, CT 06045-0191

Ronald Nijssen

As far as I know there are two separate paradigms you are dealing with
1. Domain vs. Workgroup
2. DHCP vs. fixed IP addresses

1. It should be no problem to have your scada systems on a workgroup, tip:
if the name of the workgroup is the same as the domain name then after one succesfull usage of a network resource (e.g. mapped network drive) the User - Password as it has been configured in the workgroup, and actively used, is applied to subsequent access to domain resources (e.g. printers)
You will have to keep the User Administration synchronized manually
2. A DHCP server will provide an IP address regardless if you are member of a domain or in your own workgroup. connectivity is sufficient. A problem may be that PLCs can not deal with the potentially (most of the time not, depending on the lease term) changing IP addresses of connected hosts. If this is the case then you can: a. get a static IP from your MIS group, they
can reserve an IP in their DHCP for you, b. install a second IP adapter and set a static IP on that adapter, separating your networks

Ronald Nijssen