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DHCP Renewal Failures on Switched Networks

This article was previously published under Q168455
SYMPTOMS
A client connected to an Ethernet switch may not receive a renewed DHCP IPaddress during startup. Releasing and renewing the IP address manuallyworks.

Or, a client attempting use the preboot-execution (PXE) capabilities of a network adapter to install Windows 2000 Professional from a Windows 2000-based remote installation server may not be able to receive a DHCP or Bootp offer.
CAUSE
Some Ethernet switches have a feature that checks ports for a loopcondition when ports become active (this is the learning mode for spanningtree algorithm). If a loop is found, traffic is not allowed across theport. This process of checking for a loop condition takes approximately 10-15 seconds during which the Windows NT Workstation computer appears to beon the network, yet no traffic is being passed. Additionally, some newer switch features such as Port Trunking or Port Aggregation may increase the problem. 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 broughtthe port up. You will only fail when connected directly to the switch.
RESOLUTION
To resolve this problem, disable the spanning tree algorithm feature ofyour Ethernet switch. This may not be necessary on all manufacturesswitches, some vendors may allow you to simply move spanning treeinitialization to the background. This enables the switch port to almostimmediately become functional, but still preform spanning tree discovery inthe background (non-blocking). Please note that spanning tree is onlynecessary on ports that connect to other switches (or bridges). Additionally, if Port Trunking or Port Aggregation is enabled on ports attched to DHCP clients, then either disable these features or convert the client to a static IP address if these features are required. Ports thathave only clients connected do not need spanning tree enabled. Forinformation on how to do this, please contact the switch manufacturer.
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Article ID: 168455 - Last Review: 02/20/2007 21:33:35 - Revision: 1.1

  • Microsoft Windows 2000 Server
  • Microsoft Windows 2000 Advanced Server
  • Microsoft Windows NT Server 3.51
  • Microsoft Windows NT Server 4.0 Standard Edition
  • kbnetwork kbprb KB168455
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