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Precautions for changing subnet mask?

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I work at a waste water treatment plant in the Operations department which has a Windows 2003 server. There are two subnets in use, one which is and the other The second subnet is used by the SCADA system which monitors the activity of all the machines that treat the waste water. In a separate building is the administrative staff, which has a separate Windows 2003 network and IP addressing scheme. The subnet there is 192.168.0.x. We are planning on setting up a two-way trust to allow the two networks to communicate through the SonicWALL firewalls in use at both locations. I found that the best way to have the two separate subnets co-exist on the same network is to change the subnet mask to, but what I would like to know is: Are there any precautions to keep in mind when modifying the subnet mask?



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They should be able to communicate just fine the way they are, with

Testing in my lab with this config shows no problem:

Building A - 192.168.0.x
Building B - 192.168.1.x

Subnet on both:

Both buildings firewalled.

You'll be punching a couple holes in the firewall at both locations to set up the trust, though. IIRC, it is 135, 137,139, and 389. But not sure - I'll have to check that.

Check connectivity by attaching to a share on a remote machine:

Start, Run.

If you get an authentication box, then the path is open. If you are getting in to the share straight away, you have some credentials cached. Again, path is open.

If you get a loooong pause, then a "Not Found" error, then you have some other issues going on.

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