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I manage two separate physical windows networks. I would like to allow access from one of the networks to the other as securely as possible. I am confident that the security within the respective networks is properly configured.

I want to allow access for two things specifically: exchange and server monitoring (snmp). Network "A" has exchange and the snmp monitoring software. For network "B" to get exchange, they need to go outside of the network through internet to get email. For monitoring, I currently have no way to monitor severs on Network "B", mostly due to licensing restrictions/budgeting.

The physical networks terminate in the same physical space with separate equipment. I have a Sonicwall NSA 2400 on network "A". My thought is to create an interface for network "B" on the sonicwall and NAT network "B" to network "A". This is a very simplistic overview. I would like to figure out if this would be a good way of connecting the two networks.

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Connect them on the routers, install routes, install firewall rules. Being a professional admin - what is the question about? I mean, every step is trainee baseline level. Only requirement: Unique IP Addresses, if those are not in place, happy renumbering of one network. – TomTom Jan 6 '13 at 16:27
I have unique ip's. Good thing we got rid of the people who kept telling us some backwards way of doing this...and they were self proclaimed beyond trainee! – IMAbev Jan 6 '13 at 17:06
up vote 5 down vote accepted

Yes, setting up a firewall interface makes sense. You will be able to assign that interface to a new zone and set up rules to allow and deny different types of traffic between the two LANs.

Using NAT does not make any sense at all in this context, unless both networks are using the same RFC1918 address space and neither can be renumbered. NAT would complicate matters tremendously.

If you can't monitor equipment due to budget and licensing restrictions, consider open-source monitoring solutions like Nagios and OpenNMS. They are more powerful than most of the commercial alternatives.

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