What you need to do is pick a internal IP range and stick to it.
10.0.0.0/8 (255.0.0.0)
172.16.0.0/12 (255.240.0.0)
192.168.0.0/16 (255.255.0.0)
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Then you will need think about DNS / HOST etc.
Take a look here before you get started:
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