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Active Directoy Design Advice Needed for a School

Posted on 2014-04-25
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I am the IT Manager at a school and need some advice on how to re-design/optimize the network and active directory structure.

In the past before VLANs were common, it was a requirement to seperate the Staff and Student domains for security purposes.  This resulted in 2 physically seperated lans as well as Active Directory Domains.  While this setup gives additional security, it is an outdated concept and generates a lot of administrative overhead.

I would like to merge the Staff and Student Active Directories into a single AD forest.  However, I need to prevent that the students will be able to access specific servers as well as any staff workstations.  We have Layer 3 VLAN capable switching equipment, so I suppose the best solution is to create seperate VLANs and restrict access between the VLANS.  For example:

VLAN 100 = Servers used by Staff and Students
VLAN 200 = Servers only for Staff
VLAN 300 = Staff Workstations
VLAN 400 = Student Workstations

I would then prohibit VLAN 400 to access any resources in VLAN 200 and 300.   Would this be the best practice?

For the students we're also using Google Apps and sync the passwords from our Student Domain controller.  However, internal security regulations prohibit us from installing Google Apps Password Syncs on any Domain Controller which is used for staff activities.

My question:  is there a common way to prevent a certain user group (e.g students in our case) to contact a certain Domain Controller?  

Thank you for your appreciated advice & opinions!
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Question by:MrFortune100
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Red-King earned 500 total points
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It sounds like you've got your hands full there.

I'd agree in taking the VLAN approach. It gives you much more control over your network.
Check if your Layer 3 switch can apply ACLs to the IP traffic. This way you can restrict access between the VLANs.

I'm not sure about the procedure for migrating the 2 domains into a single forest but I'm sure you'll be able to find a guide for that.

Regarding the Domain Controller for the  students, I would configure a RODC (Read Only Domain Controller) in VLAN400.
This RODC would receive AD schema updates from your other DCs but wouldn't be able to update AD itself.
You would need to ensure that the ACLs allow traffic from VLAN200 to VLAN400 but not from VLAN400 to VLAN200

To help focus your security planning it might be helpful to think of your VLANs as;

VLAN 100 = General Servers
VLAN 200 = Secure Servers
VLAN 300 = Secure Access Workstations
VLAN 400 = General Access Workstations
VLAN 500 = IT Workstations

You can then think of your ACLS as;
IT Workstations can access everything (VLAN 500 -> All VLANs)
General can access General (VLAN 100 <-> VLAN 400)
Secure can access Secure (VLAN 200 <-> VLAN 300)
Secure Servers can access General Servers (VLAN 200 -> VLAN 100)
Secure Servers can access General Workstations (VLAN 200 -> VLAN 400)
General Servers cannot access Secure Servers (VLAN 100 x VLAN 200)
General Workstations cannot access Secure Servers (VLAN 400 x VLAN 200)
General Workstations cannot access Secure Workstations (VLAN 400 x VLAN 300)
Secure Workstations cannot access General Workstations (VLAN 300 x VLAN 400)

You could also add a Wifi VLAN in the future which you would treat as either the General Workstations or as a new  even more restricted category such as guest users.

Rory
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by:MrFortune100
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Dear Rory,

Thank you very much for your advice, much appreciated.  

Yes, we have Cisco SG300 switches which support ACLs.  The "merge" will not be a problem, I'm setting up everything from scratch over the summer holidays.

Regarding the RODC, do I need to setup a separate AD site for the student LAN?

Thanks for the VLAN and ACL suggestions, this will help me a lot!
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by:Red-King
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You don't necessarily need a separate AD site for the students LAN.
While you certainly can do this, the biggest effect it will have will be to segregate your DCs. It will reduce the frequency of replication between the RODC and the other DCs.
You can assign the Student LAN subnet to your main site in the "AD Sites & Services" console.

I also remembered about this Technet article which is quite useful.
AD TCP/IP Ports: http://technet.microsoft.com/en-us/library/dd772723(v=ws.10).aspx
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by:MrFortune100
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Thank you very much for your advice!
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by:Red-King
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Glad to have helped.
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