DHCP Renewal Failures on Switched Networks

• Microsoft Windows NT Server versions 3.51 and 4.0

SYMPTOMS

A client connected to an Ethernet switch may not receive a renewed DHCP IP address during startup. Releasing and renewing the IP address manually works.

CAUSE

Some Ethernet switches have a feature that checks ports for a loop condition when ports become active (this is the learning mode for spanning tree algorithm). If a loop is found, traffic is not allowed across the port. This process of checking for a loop condition takes approximately 10- 15 seconds during which the Windows NT Workstation computer appears to be on the network, yet no traffic is being passed. The DHCPREQUEST packet (along with any other traffic during that time) is lost.

If you have a hub at the end of the port, the hub will have already brought the port up. You will only fail when connected directly to the switch.

RESOLUTION

To resolve this problem, disable the spanning tree algorithm feature of your Ethernet switch. For information on how to do this, please contact the switch manufacturer.