Had a school that reported that several computers were unable to get new IP addresses and therefore unable to logon to the domain. Their DHCP was handled by their local domain controllers with each server handling half of the /23 address space which equates to 510 total usable address for local devices on that subnet. Checked DHCP on the primary domain controller and found that their were 450+ BAD ADDRESS items in the scopes lease, so deleted these to free up space. Checked on the secondary domain controller and found that the DHCP server had a blue exclamation point on it which meant that the scopes leases were exhausted. Tried to look at the lease list and it had a red X on it and no entries listed. So how to fix this? Here is a method that I found to perform a DHCP repair / rebuild in this kind of situation:
How to Perform DHCP Repair / Rebuild
1. On the Windows DHCP server open a command prompt with administrative privileges
2. Type the following command to backup all the DHCP configurations settings:
netsh DHCP server dump>DHCPdump.txt
3. Stop the DHCP server service
4. Delete the contents of the c:\Windows\System32\DHCP folder including all subfolders.
5. Start the DHCP server.
6. In the same administrative command prompt type to restore the DHCP configuration settings:
netsh exec DHCPdump.txt
7. Then in the administrative command prompt type to run diagnostics on the DHCP scope:
netsh DHCP server initiate reconcile
8. Open up the DHCP administrator tool and check that all of the options are intact and the Reservations are present.
9. In the same administrative command prompt type to export all DHCP information to a file:
netsh DHCP server export DHCP.txt all
10. Copy this file and the DHCPdump.txt file somewhere else as a backup.
This DHCP repair worked immediately and client workstations started to register for DHCP leases again.
If your company is using Windows DHCP Servers or need help with a DHCP repair / rebuild, then contact us for assistance.