Windows DHCP Server Gives Incorrect Settings for the Default Gateway or the DNS Server

In Windows, you may experience the following behavior:

• When you use the Windows Dynamic Host Configuration Protocol (DHCP) service, the default gateway and the Domain Name System (DNS) server options may be randomly changed from the DHCP clients' configured values to the DHCP server's own IP address.
• DHCP clients may receive leases from a computer running Windows that is not running a DHCP server and does not currently have Internet Connection Sharing (ICS) enabled on any adapter.

These issues can be caused by a computer that previously had ICS enabled but from which the network adapter was removed without disabling ICS. Even though the network adapter that was being shared has been physically removed or disabled on the system, the service for ICS may still attempt to start. This attempt causes the DHCP allocator for ICS to offer leases to DHCP clients.

The ICS service needs to be stopped and disabled on the Windows-based computer providing the leases; doing this disables the DHCP allocator for ICS.

To disable the ICS service, follow these steps:

1. Click Start, point to Programs, point to Administrative Tools, and then click Services.
2. Right-click Internet Connection Sharing, and then click Properties.
3. Under Startup Type, click Disabled.
4. Under Service Status, click Stop.
5. Click OK and close the Services Microsoft Management Console (MMC).