DHCP Renewal Failures on Switched Networks

• Microsoft Windows NT Server versions 3.51, 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. This may not be necessary on all manufactures switches, some vendors may allow you to simply move spanning tree initialization to the background. This enables the switch port to almost immediately become functional, but still preform spanning tree discovery in the background (non-blocking). Please note that spanning tree is only necessary on ports that connect to other switches (or bridges). Ports that have only clients connected do not need spanning tree enabled. For information on how to do this, please contact the switch manufacturer.

Additional query words: prodnt renew catalyst

Keywords          : kbnetwork nthowto nttcp NTSrv 
Version           : winnt:3.51,4.0
Platform          : winnt 
Issue type        : 

Last Reviewed: July 8, 1999