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Firewall configuration for Domain controller communication?

Posted on 2011-02-14
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Last Modified: 2012-05-11
I've created a box to serve as my production domain controller at my data centre. The primary DCs sit at the office.

There is a VPN between the two locations and they sit on different subnets.

What modifications do I need to make to my new box's config to let it see the primary DC, and what firewall ports need opening to support full AD replication?
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Question by:Borgs8472
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by:Ryan Smith
ID: 34890364
If you have a vpn setup between the two sites it's safe to open all ports on the vpn policy.  You should probably use vpn encryption though.
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tigermatt earned 500 total points
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You have a number of options available to you:
Open all ports across the VPN link as previously suggested.
A quick and dirty fix, but also an insecure one. You should definitely use a high encryption connection between the two offices otherwise all your AD traffic is passing over the Internet in plain text, which is not secure. This also means that your data center servers could fairly easily be attacked on any weak / unpatched port, because all ports are allowed through the firewall.
Configure the server to use set RPC ports for Active Directory communications and then restrict the firewall to only allow the necessary ports.
Much more secure, a much smaller attack surface and you have complete control over what traffic passes between the two sites. It takes some additional time to plan, configure and document your AD setup using this method, but this is a more secure configuration and the one I prefer.

A document available at Microsoft explains in a lot more detail all the ports you need to open for the latter option and the registry changes required to fix the RPC ports at a particular value.
See http://technet.microsoft.com/en-us/library/bb727063.aspx for details.

Don't forget to set up Active Directory Sites and Services for the data center to ensure your DC situated there isn't contacted when the DCs at your main site are available.

-Matt
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