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2 domains same network same DHCP

Posted on 2015-02-02
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Last Modified: 2015-02-09
Hi Want to know because im not 100%, Is possible have 2 domains in the same network and use the same DHCP? or i need to separate them and use 2 different dhcp?
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Question by:PLCITS
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by:Cliff Galiher
ID: 40584324
It is possible, but not easy. Because AD relies on DNS working properly, you must statically assign DNS or manage to get the different settings to the appropriate clients (via user classes or similar.) It is often not productive to try.
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by:Lee W, MVP
ID: 40584340
First, no network even needs to use DHCP.  It does generally make things easier, but it's not a requirement.
Second, the problem with two domains sharing one DHCP server on the same logical subnet is that (in most cases) both domains have their own DNS server.  Active Directory is based on DNS for name resolution and the way DNS works, you can't have a "primary" and a "secondary" and have one fill in the blank for the other.  

There are a few ways two domains can work peacefully on the same network:
1. Install a SINGLE DNS server and have it respond to queries from all systems (ALL servers and ALL workstations must use this DNS server.  That SHOULD work (it's not a method I've done since I wouldn't be advising you to try to use two networks on the same network anyway nor would most professionals, I believe, but LOGICALLY, it should work.  (It's a common misunderstanding that Windows MUST use Windows DNS servers and DCs MUST be DNS servers - they do not - generally speaking, they SHOULD, but it's not a REQUIREMENT.  
2. Set one or both networks with static IPs or DNS servers.  Then it won't matter.
3. Properly separate the networks with separate switches and (if the purpose is to share the internet) then do so with a "double-NAT" configuration - connect your internet to one router and then each network to a separate router that shares the first one.
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Will Szymkowski earned 500 total points
ID: 40584448
A good rule of thumb is to keep your services separate from each other. If you are going to use 1 DHCP server for 2 domains you this is quite risky as now both domains are relying on a single server. Personally if you are going to do this I would be setting up a DHCP load balancing scenario where you are using split scope from each DHCP server to ensure availability.

A side from separating other services I personally like to have my DHCP roles on my domain controllers. I do this because DC's are the most critical servers in an environment. Having DHCP on them allows me to monitor AD and DHCP closely without additonal servers.

I personally would be installing a seperate DHCP servers in each domain. If resources permit i would also be installing mutliple DHCP server role and have them load balanced.

Take a look at the link following link which will illustrate in detail how to setup load balancing scopes for DHCP.

Load Balancing DHCP

Will.
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Expert Comment

by:Mahesh
ID: 40584594
One possible way:
U could separate all network switch port into TWO VLANs
May be VLAN 100 (Domain A) and VLAN 200 (Domain B)
Then installed DHCP server in each VLAN which would suffice your requirement

Another way:
Set DHCP server in any one domain with preferred dns as its own dns server only in scope options
Set conditional forwarder in both domain DNS servers pointing to each other
Suppose, if client is part of domainB, it will get directed by dns server in domainA to dns server in domainB while machine logon due to conditional forwarder
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