Name Resolution Fails on Multihomed Laptop and Docking Station

• Microsoft Windows NT Workstation versions 3.5 and 3.51
• Microsoft Windows NT Server versions 3.5 and 3.51

SYMPTOMS

Typically, this occurs in a laptop with a docking station (DS), with a network interface card (NIC) in the DS and another NIC in the laptop. With the laptop docked, both NIC drivers load. Name resolution works as expected.

If the laptop is undocked and restarted, the NIC driver for the DS fails to load and the laptop NIC loads, which is the expected behavior. Ipconfig reveals that this is now a single-homed system, with one IP address. However, name resolution has been affected.

If you are using Windows Internet Name Service (WINS) for resolution, pinging by name will generate the error 'Bad IP Address', but a NET USE will be successful.

If you are using LMHOSTS for name resolution, both PING and NET USE fail.

If the laptop is redocked and restarted, name resolution once again behaves normally. If you undock, remove the NIC driver for the DS and restart, name resolution works fine.

This problem can only be seen if both NICs have addresses on the same subnet. If they are assigned addresses from different subnets the problem does not occur, whether your laptop is docked or undocked, or whether you are using WINS or LMHOSTS for name resolution.

This problem has been reproduced in a PC where the second NIC was removed (as opposed to just undocking).

NOTE: Pinging an IP address always works in all scenarios. Only name resolution seems to be affected.

RESOLUTION

To work around this problem, use the HOSTS file instead of the LMHOSTS file for name resolution. Be sure to check the "Enable DNS for Windows Name Resolution" in the Advanced Microsoft TCP/IP Configuration dialog. You will now have names resolved no matter if the computer is docked or undocked. But, if a domain controller is not on the local subnet you will not be able to log on to the domain.

STATUS

Microsoft has confirmed this to be a problem in Windows NT version 3.51. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.