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One of my Windows Server 2003 Domain Controller seems to have died this morning. This was the only DHCP server for this particular office. I have another DC in this office.

If I set up a new DHCP server on this other DC:

  • Will it know the leases? (Maybe the information is stored in AD?)
  • Am I going to have to make everyone reboot so there are no conflicts?
  • Anything else I should consider?

3 Answers 3

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If I set up a new DHCP server on this other DC:

* Will it know the leases? (Maybe the information is stored in AD?)

The lease are stored in %systemroot%\system32\dhcp as dhcp.mdb and temp.mdb. (Reference) They are not stored in AD, and will not be replicated.

* Am I going to have to make everyone reboot so there are no conflicts?

No need. Just configure Windows DHCP to check for an existing client on that IP (right click on the server in the DHCP tool, there is an option to have Windows DHCP check up to 5 IP's before handing one out).

* Anything else I should consider?

Configure a secondary backup DHCP server using the 80/20 rule. Printers should have their IP's statically assigned (now is a great time to check!), as should other essential system hardware (routers, WAP's, etc).

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  • like your second point
    – Chopper3
    Aug 17, 2009 at 13:28
  • Due to how Windows DHCP server works -- you are likely to get clients who will fail to retrieve an IP address due to the reserveration checking. I believe Windows is stupid and will check 5 sequential IP's, which might all be in use. If you have users who "can't get an IP", have them reboot (or, alternatively, issue a ipconfig /renew all on their machine) so Windows will re-query your DHCP server for another IP. This might happen a couple of times depending on the size of your network until Windows has a good list of in-use IP addresses.
    – SirStan
    Aug 17, 2009 at 13:33
  • Anyone know if a recovery (windows recovery console) would overwrite the dhcp file? Aug 17, 2009 at 13:34
  • Any when you say check 'on that IP', that means I can only set 5 ip address to check first? Or does it mean it will always check an ip before handing it out ... Aug 17, 2009 at 13:35
  • Kyle, I'd say that recovery would leave it in place myself, besides even if it doesn't you're no further back, give it a try - how dead is the server?
    – Chopper3
    Aug 17, 2009 at 14:01
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I'm pretty sure the scopes aren't stored in AD sorry but if you can duplicate them quickly and accurately enough then you shouldn't need to force any reboots/manual-DHCP-renews on your users. The main thing I'd consider is whether there were any reservations in place as they'll screw you over if they're for servers/printers/other-important-devices; which they often are.

I'll try to add some more information to this answer in the next few minutes, just didn't want to leave you panicking :)

Just found that the data is stored at %systemroot%\system32\dhcp\dhcp.mdb, might you have a backup?

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  • Ya, I think I remember where the reservation cut off was. But won't I get DHCP conflicts? Since users already have reservations. If user A doesn't restart and user B does, what stops user B from getting user A's IP. I didn't think DHCP checked first ... but maybe windows dhcp does? Aug 17, 2009 at 13:22
  • No backup for this one. Aug 17, 2009 at 13:24
  • good point, if you have a wide enough IP range (say 200 IPs for 100 clients) then you could start the new scope at 101 assuming that the existing users are 1-100 and when everyone's within 101-200 then open up the scope back to 1-200 and they'll migrate to the larger scope. Of course if you're tight on IP addresses that's of no use sorry.
    – Chopper3
    Aug 17, 2009 at 13:25
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if you get bad addresses coming up, these are just because the dhcp server has detected a conflict (because it previously didn't know the address was already allocated). this is normal, they will disappear as those machines connect up and re-request their current IP.

You might get some lingering bad addresses from machines that don't rerequest their IP, in this case after a few days, just delete the other bad addresses

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