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Redundant DHCP Server Setup on Windows 2003 Network

Posted on 2006-07-11
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Last Modified: 2010-04-18
I have Windows SBS 2003 and I have a member Windows 2003 server.  I have setup active directory on both servers (with SBS being primary of course) and also setup my member 2003 server to be a secondary DNS server.  I have two subnets for two virtual lans that SBS 2003 server acts as a DHCP server for.  

My question is how can I setup a redundant DHCP server on my 2003 member server in the event that my main server goes down.  I ask this because this recently happened and it created mass chaos for the client computers. From what I understand, SBS won't allow more than 1 DHCP server on the network.  Some people have said to setup two DHCP servers to dish out different ranges on the same subnet, but this won't work according to what I have heard from others since SBS supposedly has this 1 DHCP server limitation.

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Question by:benbecker
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by:NJComputerNetworks
ID: 17084692
Add the DHCP service on the second machine... authorize it.  setup two DHCP servers to dish out different ranges on the same subnet.  Just make sure these don't overlap.
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NJComputerNetworks earned 63 total points
ID: 17084702
To add more redundancy, make the member server a domain controller by running DCPROMO and add it as an additional DC of your domain.

(Things you can't do...  are like moving Exchange to a remote server...or SQL..etc...these must remain on the SBS server.)
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by:benbecker
ID: 17084737
When you say to authorize it, how is this done?  Also, will SBS allow more than 1 DHCP server on the network?  is that what authorizing will do?

Also on my member server, i added the server role of active directory, it had me go through a wizard and reboot, I am assuming I am good to go on the active directory side.  I also checked the global catalogue option as well, so I think I'm good there.  I just need redundant DHCP so I don't have to touch my clients in time of disaster.  Last time I was scrambling around assigning static IPs and messing with a bunch of piddly things that wasted my cycles that could have been sent assessing the disaster.  I'm trying to avoid this with the redundant DHCP.
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by:Steve Knight
Steve Knight earned 62 total points
ID: 17088880
To authorise you right click on the DHCP server in the DHCP MMC snap-in and choose authorise.  Gives a list of authorised servers and you can authorise others.  Can't say any of my SBS 200x shops have more than one DHCP server running so don't know if it will accept a second but it would be cray if it didn't.

With 2003 you can amend the scopes after they are created OK so no need to create a scope with lots of excluded addresses in, just one with x.x.x.50 to 100 and the other with 101 to 150 etc. for both subnets.  Your VLAN Layer 3 switch or routing device will have a DHCP helper setup which tells the clients on the other subnets where to send their DHCP requests.  That needs amending from your one current server to instead pointing to both -- normally you can just add multiple iP's.  Both servers will get the request, both will respond and the first to do so will be accepted by the client.

As you probably know with DHCP:

Initially the client broadcasts, then periodcially it sends a packet direct to the dhcp server that allocated the address a request for renewal.  If this fails all the way up to the end of the lease time then another broadcast is sent which would then be answered by the other server and the client gets a new address.

In theory if you set a long lease time then clients will retain the address but in practice Windows 200x and above by default release the address when shutting down afaik - really annoying when the dhcp server is down and some idiot tells everyone who is happily working to shutdown...

Steve
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by:benbecker
ID: 17089781
Steve, I think we're all set and I can't agree with you more about how dumb it is that W2k and above go out to get a new IP on the reboot.  I was able to authorize the second DHCP server and used the 80/20 rule to setup the exlcusion ranges and everything seems to be functioning.  We unplugged and our main server from the network and did a test and it looks like my backup domain controller, dns and dhcp server kicked in.  We did notice that logging in did seem to take longer than usual, but at least we didn't get the dreaded no domain controllers can be reached issue.

Thanks a ton for the help!
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