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dhcp server 2008

Posted on 2011-04-29
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Last Modified: 2012-05-11
Here is the situation:
I have 2 2003 server DCs and I just added 2 2008 DC Servers in my domain (same site).

I exported and then imported the dhcp scope settings from the 2 2003 servers to 2 of the 2008 servers and everything is running fine - so it's like a mirror now so to speak. ALL dhcp servers are authorized.
After a few days of no reported problems, everything running fine, I decided today to unauthorize both of the 2003 dhcp servers. Soon after a few clients were having problems, no ip address. I saw active leases on all 4 dhcp servers. I performed an ipconfig /release and /renew. Restarted the clients, restared the dhcp services, restarted the servers and still they cant get an ip address from a certain subnet on the 2008 dhcp server.Nothing in my infrastructure has changed.
I have 7 scopes on each dhcp server. What can be the problem???

I read that I may need to enable the 2008 relay boot agent? But it says it cannot be done on the server that is hosting dhcp. So where does this need to be enabled? Also, this is on a lan that has vlans on switches but there is no router dividing the clients from the dhcp servers and I did see many active leases on the 2008 server so it leads me to belive this 2008 relay boot agent is not the issue.

Also, yes there is a scope of the ip range that is the same as the ip address of the dhcp server.

Help, thanks!

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Question by:tolinrome
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laloceh earned 1000 total points
ID: 35495050
DHCP clients find DHCP server via broadcast.

Broadcast does not pass through VLANs, as you don´t have a router you need to have a DHCP server per VLAN or configure a DHCP relay agent to send the DHCP messages to the DHCP server on another VLAN

DHCP Relay Agent
http://technet.microsoft.com/en-us/library/cc783103%28WS.10%29.aspx
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by:Adam Brown
Adam Brown earned 1000 total points
ID: 35495060
You probably need to take a look at the relay settings for your routers. In order for DHCP relay to go into a subnet, a BOOTP capable device needs to know where the DHCP server is. More than likely, the subnet that is having issues is still trying to relay DHCP info from the old server instead of the new.
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by:Adam Brown
ID: 35495079
Short quick lesson on DHCP: DHCP broadcasts on a single subnet. In order for clients on a second subnet to obtain a DHCP lease, there needs to be a DHCP Relay agent *between* the subnets. This is usually a router. The DHCP Relay agent will detect DHCP Request broadcasts and forward them to the DHCP server that it is configured to send it to. From there, the DHCP server is able to determine which scope the client is on and therefore which address it will need.

In short, you will never need to install DHCP Relay Agent on windows 2008 unless you are (for some crazy reason) using Windows as a router between subnets.
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by:tolinrome
ID: 35495497
hmm alot of good information here, thanks.
im still wondering though the 2003 servers are on the same subnet as the 2008 servers so if were using dhcp relay (which i assume we are) then it should work since all I did was add 2 new dc's (w/dhcp server). I havent touched the vlans in the cisco switches...
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Expert Comment

by:Adam Brown
ID: 35495531
Well, that's the thing, if you have VLANs between your subnets, then you have to have some routing for the subnets to communicate with one another. If the Routers that are providing that communication have the old server configured as the destination for DHCP Relay, DHCP won't pass to any subnets but the ones it can see (and vice versa).
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by:tolinrome
ID: 35495543
Ok, now I see..I'll have to wait until monday to chack it out. thanks.
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by:tolinrome
ID: 35508161
That was it, thanks guys.
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