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Can I have a DHCP server in each non-contiguous tree in the same forest??

Can I have 2 different DHCP servers if I have 2 trees in the same forest and route between the 2??  The DHCP server would not interfere with each other would they??  The forest root domain will be running exchange which the other domain needs to use.  Is it a bad idea to have them on two different subnets??
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debbiez
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debbiez
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1 Solution
 
LauraEHunterMVPCommented:
Multiple DHCP servers in a single AD forest are a non-issue.  DHCP operates at the network level, and so really doesn't care much about AD as long as each server is authorized within AD.

Not only is it not a bad idea to have them on 2 different subnets, it is actually a much worse idea to have them on the -same- subnet, as they will interfere with one another.
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cj_1969Commented:
Just make sure your network is not setup to relay DHCP requests.
Even on the same network multiple DHCP servers are fine as long as the range of addresses they are assigning do not overlap ... this is actually the only way to implement redundancy for DHCP that I know of.  When I set them Up I just configured the same scope of address on each and excluded the first half of the addresses in the scope from one machine and the second half from the second machine ... worked like a charm  :)  You just want to make sure that the 1/2 range is enough to handle all the machine in the subnet in the case of a failure of one of the servers ... so you would use a x.x.x.254 subnet for a normal class C range for best results.

For the other part of your question, this should not have any effect on Exchange.
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debbiezAuthor Commented:
I know this may sound stupid but how do the PC's in domain 2 now not to obtain an IP address from domain 1??  Is based on the domain they are joined in??
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debbiezAuthor Commented:
So I can still have them on different subnets but have domain 2 use the exchange server on domain 1 correct??
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LauraEHunterMVPCommented:
> Is based on the domain they are joined in??

Nope.  AD has no relevance to a PC obtaining an IP address from TCP/IP.  Client boots up, broadcasts for a DHCP server and obtains an address before it even thinks to go looking for a domain controller to log into.

DHCP configuration is a function of the physical network, not the network operating system that's in use.
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Zenith63Commented:
"I know this may sound stupid but how do the PC's in domain 2 now not to obtain an IP address from domain 1??  Is based on the domain they are joined in??"
They won't know if you have the two DHCP servers in the same network segment (ie. if all your clients and both DHCP servers are connected to a single LAN.).

Generally you use multiple DHCP servers giving addresses in seperate subnets when you have more then one network segment (eg. you have two buildings or your LAN is split in two by a router).  In this case PCs in site 1 can't talk to the DHCP server in site 2 so can only get an IP from their local DHCP server.
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klulue123Commented:
As it has been said before, it is best to have separate DHCP servers on the separate subnets, the only thing you need to make sure of is that you have a router between the subnets so that traffic can flow  in both directions.  Then yes, domain 2 can use the same Exchange server as domain 1.
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LauraEHunterMVPCommented:
If it has been said before, why the need to re-iterate without adding any additional information?
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debbiezAuthor Commented:
So if there is a router in place between the 2 sites, and both sites have a DHCP server... how is it that clients from site B will never get answered from the DHCP server in site A if there is routing going on and the 2 networks can talk to each other?
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klulue123Commented:
DHCP requests are a broadcast and the router blocks broadcasts.
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cj_1969Commented:
You can use a single DHCP server though ...
on your router you can configure it to pass the DHCP request on to the DHCP server.
In this configuration you tell it what subnet the request is for.
In your DHCP server you set up a set of addresses for that subnet.  
The DHCP server is smart enough to know to pull an address from the correct pool of addresses depending on if it received the request directly or as a relay message.

That said ... DHCP and IP address assignment has no bearing on accessing Exchange.  As long as the client machine has an IP address and your network is set up to route packets to the LAN that Exchange is on you'll be good.

So, to summarize ...
If the LAN segments are serperated by a router then the simplest solution is a DHCP server on each LAN segment.  The LAN segments do not affect your ability to impliment AD or Exchange.
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You can configure both DHCP subnet scopes on one DHCP server and set up your router to forward DHCP requests.

As long as your domain controllers and any other servers are configured in WINS/DNS so that they can be looked up by name to get the IP and the IP is reachable, either onthe same subnet or via router, then you are fine.

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