Troubleshooting TCP/IP Address Conflicts

Kenn's
Tech
Notes

19991009: Troubleshooting TCP/IP Address Conflicts

October/1999
Tech Note #9

For the most part, we don't have to worry too much about TCP/IP addresses on our networks, since we use DHCP to assign the addresses automatically. Every once in awhile, however, it is possible to get a conflict. This can happen if you copy a master hard drive image that was created on a machine had an active IP lease (you should always release your IP configuration before mastering a hard drive). When Windows starts it gives a message saying that there is a "conflict for the IP address aaa.bbb.ccc.ddd with the system at hardware address ee:ff:gg:hh:ii:jj. The interface will be disabled." The final statement means that TCP/IP will not work on the workstation. If no other network protocol is installed, you will not have network connectivity. Otherwise, you will only lose network access in TCP/IP-dependent apps such as web browsers and e-mail clients.

This is a DHCP problem. This happens when more than one workstation claims a lease for the same IP address. It is not always that easy to fix. There are a number of different strategies.

a. Use winipcfg to "release all" on both systems claiming the same address. You already know one of them (the one with the error). To find the other, run the following command at the DOS prompt on a workstation that is functioning:

nbtstat -A aaa.bbb.ccc.ddd

(where aaa.bbb.ccc.ddd is the address shown in the error message.) Note that that line is case-sensitive.

Or, you can generally find the computer name for an IP address by checking active leases in DHCP Manager on the DHCP server, or by viewing the database in WINS Manager on a WINS server.

Once both workstations have released the addresses, power them both down. After they have both shut down, power them both up. If you're lucky, they will take different addresses.

If you still get the error proceed to step b.

b. Run DHCP Manager on your DHCP server and reserve the address aaa.bbb.ccc.ddd in your DHCP scope. Reboot the two workstations again. If the problem is solved, you should still leave the reservation in place for a week or two. After that time, you can remove the reservation.

If you still get the error proceed to step c.

c. On both the problem workstations, run REGEDIT. Go to HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Vxd

Delete the key DHCP and delete the key DHCPOptions. Power both workstations down. When they have both shut down properly, power them up.

If you still get the error proceed to step d.

d. Reinstall Windows clean on one of the two workstations. Make sure you delete the existing Windows directory.

If you still get the error proceed to step e.

e. Reinstall Windows clean on the other workstation. Make sure you delete the existing Windows directory.

If you still get the error proceed to step a. ;-)

DISCLAIMER: This document is intended for the reference of computer support personnel within Winnipeg School Division No. 1. There is no warranty or liability if procedures recommended here have an adverse affect on any systems. Use them at your own risk. Any trademarks mentioned are the property of their owners, none of whom have certified any information provided here. Opinions expressed here are personal only and do not represent the policy of Winnipeg School Division No. 1 or any other organization anywhere.

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2001 June 9

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