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Setting up a secondary DHCP server in a single subnet network.

Posted on 2008-09-30
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We are looking to create a backup DHCP server on a single subnet network. I set server1 to give out IPs in range 10.0.0.100 to 10.0.0.195 and server2 to give out 10.0.0.196 to 10.0.0.220. Is there a way to delay the response of server2 so that server1 will always respond first to IP request, unless of course it is down?

We have a 6 day lease setup on IPs. The OS is windows 2003 standard. Both DHCP servers act as DC.

We do not want to create mutliple subnets or have to route traffic.

Thanks
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Question by:EJC9999
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by:Justin Durrant
ID: 22609011
I wouldn't worry to much about setting up another DHCP server. Best thing for you to do is create a backup of your DHCP database and keep it handy in case you will ever need to restore it (I very much doubt you will ever use it though, DHCP is quite reliable).

You are going to waste your time and resources by trying to provide some kind of redudancy given the size of your network.

There is no "primary" or "Secondary" DHCP. If you create and enable a scope in a server(s) and  then they all will respond to clients with a DHCPoffer packet the client then accepts the offer in a"first come first accept basis".
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by:MikeKane
ID: 22609068
You can deploy a 2nd DHCP in the same subnet.   Microsoft has an 80/20 rule for this scenario and a DHCP cluster solution as well.  

Read this to get started:
http://technet.microsoft.com/en-us/library/cc778572.aspx

Also has good info:        
http://www.madboa.com/geek/dhcp-failover/
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by:KCTS
ID: 22609084
If you do set up two DHCP servers then why bother about a delay - why does it matter which server responds
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by:EJC9999
ID: 22609431
It matters if  server2 is answering first to all request. Then it will give out the 20% of IPs that it has. When and IF server1 fails, server2 will not have any IPs to lease because it is full.

If it was possible to estable a secondary/primary or delay, then server2 would only give out an IP if server1 was down.

I didnt think there was a good solution or easy fix to this but I wanted to be sure. I know we will probably never need the second DHCP server but if we could have it , we want it.

Thanks for the responses.
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by:MikeKane
ID: 22609661
Its usually just better to add a decent lease time and get good backups of the database.   Restoring it to a working DHCP is a pretty straightforward process...
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KCTS earned 350 total points
ID: 22609730
If you have two DHCP servers on the same same subnet you can split the scope 50/50. If you have two subnets with a DHCP server on both then you can use a DHCP relay agent where you can incorporate a delay, and where it makes sense to split the scope 80/20
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