How do I configure my DHCP server correctly in this network?

IntoFOS
IntoFOS used Ask the Experts™
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Hi all,

I have a strange problem.
I have installed a new DHCP server in windows server 2008 but the clients are not receiving any addresses.

Possible strange points:
The server has only 1 NIC and this is configured with 2 IP addresses
Their network uses a switch that routes all of their traffic between several subnets.
They have a broadband router with DHCP configured that clients can receive IP addresses from.

I thought it was a network issue so I did the following:
stopped the DHCP service on the server and plugged the broadband router into the same switch that the DHCP server is plugged into.
Then I plugged my laptop into the same switch and I was able to get an IP through the DHCP of the broadband router.

However when I deactivate the DHCP in the router and start the DHCP server service on the windows 2008 server I cannot get an IP from the server.
So the problem is the windows server.

The DHCP role installed perfectly when I added it and there are no errors in the logs.

Can this be an error with the fact that there are 2 IP addresses configured for the NIC?
When I look at the binding for the server I can only see 1 IP listed.

During the installation I remember it asked me which IP to bind to but it only gave me 1 IP in the list and this IP was different from the IP I can see listed as being bound.

Can I get this configuration to work (DHCP on a server with 2 IPs on the same NIC) by changing the binding somehow?

Does anyone have any ideas?

Tomorrow I will be attempting to completely reinstall DHCP on this server again.

Cheers
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AkhaterSolutions Architect

Commented:
when you say the server has 2 IPs are they from the same subnet or from different subnets ?

Is your DHCP server part of an Active Directory domain? if so have you authorize it ?

Commented:
Yes, as Akhater said, DHCP in domain has to be authroised before it can assign IP address in domain.

DHCP register it services into AD by making it authorize & in domain withpur authorization dhcp will not work.

You can check is there any other dhcp cconfigured into domain,if yes remove the old authorised dhcp server from ADSIEDIT.MSC

The article apply for windows 2008 also.
http://support.microsoft.com/kb/306925

Note: In a domain two dhcp server can't be authorised at a time for single subnet.


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AkhaterSolutions Architect

Commented:
"Note: In a domain two dhcp server can't be authorised at a time for single subnet."

I am sure you mean "should not" because technically speaking there are no restrictions for this

Author

Commented:
Hi all,
Thanks for the comments.
The server has been configured exactly per the links provided, is authorized in AD and the scope is activated.
I reinstalled the DHCP role after removing one IP address (so there is now only 1 IP to bind to) but clients still will not get an IP from the scope.
I installed the DHCP service on a Windows 2003 server outside the domain but on the same switch and clients could receive IPs from that server.
I have been told that both servers are on the same LAN (with different IPs) but DHCP just will not work on the Win 2008 server.
There are no errors in the event log and the server appears as though it has been setup correctly but it won´t work.
Does anyone have any other ideas as I am completely lost.
I still think it is a problem with the routing but I cannot prove it at the moment.
Regards
AkhaterSolutions Architect

Commented:
if your DHCP is authorized and you didn't remove it there is no way the other windows 2003 server outside the domain be able to lease IPs.

Taking a wild guess is the 2008 server in the same subnet (what you would call LAN) as the clients it is trying to server? I think not. if this is the case then you need to define a relay agent/ip helper address in each subnet

Author

Commented:
Hi Akhater,
Sorry for the confusion.
 
I have done some more tests.
They have a router that has static routes configured between all subnets.
The Win 2008 DHCP server connected to the domain = 10.202.52.x
The Win 2003 DHCP server standalone = 172.15.3.x
The test that was carried out before was with a scope configured for the same subnet as the Win 2003 server and it worked.
I then tried the same scope (172.15.10.x) on the Win 2008 DHCP server (10.202.52.x) without success.
Then I tried a new test scope on the 2008 DHCP server using 10.202.52.x and the clients could receive an IP.
Looks like I need to enable the DHCP Relay service somewhere.
This needs to be enabled on the router so I will ask them to do it.
Thanks for all your help and I will let you know what happens.
Cheers
Solutions Architect
Commented:
exactly my thoughts the DHCP server and the clients trying to get the IP are not on the same subnet,

so yea you need to configure your router with ip helper address the IP of your DHCP server and it will work

Author

Commented:
Hi again,
I got the people here to configure the DHCP Server IP address on the router as the IP Helper-Address and now progress has been made.
Using wireless it is working fine.
However using the LAN, the server assigns an IP address but the client never receives it. It appears that the DHCP Offer packet is never reaching the client.
Is it possible that the router is not allowing this packet to pass for the LAN?
I am getting confused now as the Offer packet is a broadcast too isn´t it?
Thanks

Author

Commented:
Akhater,
I have closed this question as it does not seem to be a DHCP issue any more. Thank you for your help and thanks to the other posters as well.
The issue is routing between the subnets that exist in this network. They need to sort this out before DHCP can start functioning as expected.
Cheers
Mark
AkhaterSolutions Architect

Commented:
keep us posted and thanks for the followup

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