DHCP Server Performance Degraded by Large Number of Scopes

• Microsoft Windows NT Workstation version 4.0
• Microsoft Windows NT Server version 4.0

SYMPTOMS

When a large number (hundreds) of scopes are configured on a Windows NT 4.0 DHCP server, performance degrades to where it cannot keep up with large client loads such as those experienced after a power failure, or at peak network startup times.

CAUSE

A list of scopes is maintained in the registry. When a DHCP DISCOVER or DHCP REQUEST is received, it must be matched against the configured scopes to see if the server is able to provide services to the client subnet. This process of searching through the scopes was not optimized for large numbers of scopes. Additionally, some database calls could experience suboptimal performance caused by nonoptimal database buffer initialization.

RESOLUTION

To resolve this problem, obtain the following fix or wait for the next Windows NT service pack.

This fix should have the following time stamp:

   03/03/98  03:52p              118,544 Dhcpssvc.dll (Intel)
   03/03/98  03:49p              189,712 Dhcpssvc.dll (Alpha)

NOTE: This hotfix supersedes the fixes referred to in the following articles in the Microsoft Knowledge Base:

   ARTICLE-ID: Q141496
   TITLE     : DHCP Client Comment Disappears When Obtaining IP Address

   ARTICLE-ID: Q167708
   TITLE     : BootP Client Names Disappear in DHCP Manager

   ARTICLE-ID: Q163055
   TITLE     : DHCP Client May Fail with WinNT 4.0 SP2 Multinetted DHCP
               Server

   ARTICLE-ID: Q175035
   TITLE     : Diskless Workstations Cannot Find BOOTP Server with DHCP

STATUS

Microsoft has confirmed this to be a problem in Windows NT version 4.0. A supported fix is now available, but has not been fully regression tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Technical Support for more information.

MORE INFORMATION

The updated file caches the entire scope list in memory, and uses a binary search to quickly determine if the server has a scope that is relevant to each client request. This update dramatically reduces the number of times that registry keys are opened and searched. It also provides more buffers for interaction with the database, which improves database throughput.