DHCP Requests Fail on Logically Multihomed Server (Single NIC)

• Microsoft Windows NT Workstation version 3.5, 3.51, and 4.0
• Microsoft Windows NT Server version 3.5, 3.51, and 4.0

SYMPTOMS

Windows NT Dynamic Host Configuration Protocol (DHCP) client IP address lease requests fails on a multihomed server configured with multiple logical IP networks on a single network interface card (NIC).

This logical multihomed system is a Windows NT Server with a single NIC configured with multiple IP addresses for one physical segment. If this server is also functioning as a DHCP server with active scopes configured for each logical IP network, DHCP client requests are filled until the scope defining the first logical IP address pool is exhausted. Further DHCP client requests fail to be filled from the pool of IP addresses available from the second or higher logical IP network scopes.

RESOLUTION

To resolve this problem, install a NIC in the DHCP server for each logical segment. Each NIC should be connected to the same physical segment and assigned only one logical IP address. As DHCP scopes are created they will be made available to the clients via the network interface card at this IP network. Also verify that IP routing has been enabled on this multihomed DHCP server.

STATUS

This is by design. This forces clients residing on a physical segment to acquire IP addresses that are within the same IP network scope.

More Information Microsoft Windows NT Server 4.0 Service Pack 2 includes the ability to create DHCP superscopes, which allows the administrator to group scopes together. This eliminates the need of multiple adapters to service multiple scopes.

For more information on superscopes, please see the following article in the Microsoft Knowledge Base:

Article : Q161571 Description: Using DHCP "Superscopes" to Serve Multiple Logical Subnets