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Moving to DHCP 80/20

Posted on 2011-09-14
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Last Modified: 2012-05-12
We are splitting our windows  2003 DHCP scopes (20 scopes in total) and moving them to two new 2008 DHCP servers (to retire the old 2003 DHCP server)
We are trying to decide whether we need a maintenance window for our 24/7 1000 node environment.
Let’s say the scope 192.168.1.0 is already leased to DHCP clients by DHCP1, so we come and exclude it from DHCP1 and Add it to DHCP2 and DHCP3 (80/20) should we expect any interruptions or conflicts for the clients with such a move? Or is it gonna be completely transparent for the clients.

Any one can share a previous experience for a similar change?
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Question by:Maroin
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Expert Comment

by:jgibbar
ID: 36540807
**Note These suggestions are based on experiences with a DHCP Appliance and not Windows DHCP Services**

I would move a whole scope at a time as opposed to pieces of the whole from my recent experiences. Since you are using a different IP address for your server, the clients will still attempt to renew their IP address on the old server after the TTL expires. When the addresses are no longer active on that server, the client will initiate a new DHCP Request and get an IP address from which ever relay device answers. If you are trying to use all three at the same time, DHCP1 might reply before 2 or 3.

 If you want to ensure these clients get he same IP address, you may need to do MAC based Reservation for each host else it will hand out the addresses as the DHCP Server sees fit.
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pwindell earned 500 total points
ID: 37018201
I'd forget the 80/20 and go 50/50.  I have never thought 80/20 was ever a good idea,...what happens if you loose the one giving 80%?,...how long is the one with 20% going to hang on before it runs out?,...and that's assuming it doesn't already run out even while both are running.  

If you go to the Properties of the individual DHCP Server and look on the Advanced Tab you should see the settings for Conflict Detection Attempts. Mine is set to 3,...I assume it is the default because I don't remember ever changing it.  This item is supposed to have the DHCP Server ping an IP 3 times to see if it is not in use before giving it out to a Client.

So in the long run there shouldn't be any serious problems.  Your most important machine on the LAN (the Servers) should always be static entries anyway.  If a workstation has a conflict just reboot it and it should come up with a different IP#, it isn't going to be the end of the world.
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Author Comment

by:Maroin
ID: 37256864
I've requested that this question be deleted for the following reason:

Thanks for responding, unfortunatily my question was not answered, but it's OK since we have decided to go on another direction and change the IP address subnets so no conflict is expected anyway.
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Expert Comment

by:pwindell
ID: 37256866
I think the question was answered.  Just because the OP did not choose the follow our advise does not mean it wasn't answeres.   If the answer was just simply not what he wanted to hear, then that is an entirely different thing.
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Author Comment

by:Maroin
ID: 37256955
Thanks Pwindell for your feedback,

The question was not for you to provide solutions, the question was if you have done a similar change and did you end up having any downtime:

To explain, here is a quote from my question, if you can answer it I will consider it answered:
{
We are trying to decide whether we need a maintenance window for our 24/7 1000 node environment.
Let’s say the scope 192.168.1.0 is already leased to DHCP clients by DHCP1, so we come and exclude it from DHCP1 and Add it to DHCP2 and DHCP3 (80/20) should we expect any interruptions or conflicts for the clients with such a move? Or is it gonna be completely transparent for the clients.

Any one can share a previous experience for a similar change?
}


So:
1) do we need a maintanance window?
2) should we expect any interruptions or conflicts for the clients with such a move? Or is it gonna be completely transparent for the clients.
3) Did you have a previous experience for a similar change that you can share (i.e. did you split a scope)?

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Expert Comment

by:pwindell
ID: 37257886
I covered #1 and #2.  I did not mention anything about #3 although I have done it myself

At least that is the way I viewed what I was writing.
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Author Closing Comment

by:Maroin
ID: 37258809
Thanks
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