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Retire old DHCP server

We have two DHCP servers in use each with it's own separate scope.   A Windows Server 2000, and 2008 R2.  

We would like to retire the Windows 2000 server and transfer all leases to the 2008 server.  

There are currently about 100 leases on the 2000 server and 50 on the 2008 server.   There are not currently enough available IP address to add to the 2008 server to accommodated the clients currently leased out by the 2000 server.

What is the recommended way to do this without overwriting the current scope on the 2008 server?  (which transferring the database would do correct?)

We do not plan to add a second dhcp server to replace the ageing 2000 server.   We want to remove the 2000 server before it has any hardware issues since we do not have a support contract for it.

to make the problem more clear:

It is my understanding that a dhcp client will keep it's lease until it expires, and if we add the scope to the new server it will try assigning IP's that are still in use from un-expired leases on the old server.   This would result in IP conflicts which we absoutly can not have.  This needs to be seamless and without having to log on to each PC and do a ipconfig /renew.

Thanks!

ANY thoughts or comments are appreciated,  but I am looking for a step-by-step plan that we can follow and have the least amount of potential things to go wrong as possible.  
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sonic4269
Asked:
sonic4269
1 Solution
 
sonic4269Author Commented:
I will reward points within 24 hours to the best answer.  
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maxxmyerCommented:
If both servers are on the same network, Add the new scope to the newer server and set “conflict detection attempts” from 0 to 2.
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lrpageCommented:
one lazy way to handle this.  Shorted your dhcp leases to 1 day.  Then on Friday or Saturday make all your changes.  By the time people come in on Monday their lease is up and they get a new one from the new server.  You can change the lease back later.

could always put ipconfig /release then /renew in your login scripts to ease the transition

not sure what your scopes are but here is a scenerio that may work

server 2008 hands out 1-50
server 2000 hands out 51-150

setup the 2008 to also do 151-250.  Then there are enough for everyone and no overlap
Turn off the 2000 at will
you can adjust the scopes later if you want it to be more organized.
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sonic4269Author Commented:
Yes same network. Upon reading about this option this solution looks to be acceptable,  however would you mind providing more information?    What are some possible downsides to this?  I see it can add a delay to the leasing  process,  along with generating "Bad Address" leases in the server.  

Would you recommend disabling this option after all PC's renew on the new server?  

Would you recommend setting the lease period on the old server to 1 day ahead of time,  so all clients will transfer as soon as possible or would it be better to leave the lease duration at default and let them slowly migrate over?

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Stelian StanCommented:
What you can do is to create a new scope on the 2008 server and shrink the one is already there. Change the lease on the old scope (2008 DHCP server) to couple of hours. Wait till all the leases from old scope are migrated to the new one.

On the 200 DHCP server you can execute this command to export the reservations.
netsh dhcp server <serverIPAddress> scope <scopeAddress>  dump>reserv.txt

Copy the reserv.txt file to Windows 2008 box. Open up the text file and replace changing the IP address from the old to the new Windows 2008 server, and then save the file.
Now on the target machine, do a
netsh exec reserv.txt
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sonic4269Author Commented:
My last comment was directed at maxxmyer.

lrpage:  I have thought of your solution,  but we have to many static address's all over the place that this would be a headache to manage(adding a an additional scope) if not imposable.  

I don't want to cause delays or issues with batch scripts.   that would mean until all computers reboot and the script removed all pc's would renew on every reboot.  I can see to many issues with that going wrong or causing delays on login.

I am worried that even if done on a Friday and leases expire in 1 day we may still end up with "ip address conflict messages" on the client.   This is a physicians office also with some physician working during the weekend and not wanting to be disturbed.    this really needs to be as painless as possible.
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maxxmyerCommented:
More information? of course. I will answer in order, the “Bad Address” will be coming from already leased addresses.  I don’t set “conflict detection attempts” to 0 my complicated networks, I do set to 1. I would recommend shorting the lease period on the old server right away. In addition, on the new server, include the entire scope when defining your available address pool.  Then use exclutions for those addresses that should not be included in the lease pool, and add any appropriate reservations.
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sonic4269Author Commented:
What if a machine is turned off so a new client passes the conflict resolution check,  then the old client is turned back on?  Will the old machine that was off automatically request a new lease/ip?

I think i know the answer to this but if it's not clear by now I am trying to be 100% sure before I do anything, so I appreciate being humored here.  :)


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maxxmyerCommented:
I understand your ‘what if’ concerns. I personally don’t think computers are an exact science. With that, I cannot give a 100% guarantee for the powered off workstations. It also would not concern me too much.
The default lease duration is 8 days. (don’t know what your old one currently is). The workstation will start looking to renew after 4 days. Resetting the old DHCP scope to 1 day will affect the workstations that renew. After which they will start looking to renew after 12 hours. When an IP Address lease is release, the DHCP server will hold the IP address for another 4 hour grace period, then will release the address during the next cleanup cycle (every 60 minutes). With all that, I would answer YES to the machine requesting a new lease.
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sonic4269Author Commented:
So we could be looking at some IP's that get temporarily held and can't be used right?   With the old leases expiring so quickly I could see running out when "bad address's" are generated since we are very close to the max as it is.

Not sure if there is a solution to that but I don't think it would be a major issue.    I would be able to do on the weekend and have most machines turned off before hand to help control how fast new leases are created if it's getting to close.  (right?)



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maxxmyerCommented:
Are you doing this, this weekend?
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sonic4269Author Commented:
yes but the office will still be running skeleton crew.  
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maxxmyerCommented:
A little late to change the old DHCP to 1 dy lease.
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maxxmyerCommented:
I wont be availble to assist over the weekend, many others will tho friend.
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