NDIS 5.x Intermediate Filter drivers are incompatible with Network Load Balancing (NLB.SYS)

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The Microsoft Network Load Balancer (NLB.SYS) is incompatible with NDIS 5.0 and NDIS 5.1 Intermediate Filter drivers.

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Use of any product that employs an NDIS 5.x Intermediate Filter driver, based on the DDK/WDK sample PASSTHRU, will cause the Microsoft Network Load Balancer (NLB) driver to fail.  NDIS IM Filter drivers are used in many firewall, antivirus and VPN products.  Windows Vista, Windows Server 2008 and all operating systems following, use NDIS 6.  While NDIS 5 components are supported in NDIS 6 environments, there are limitations.  A NDIS IM filter should be ported to either a NDIS 6 Lightweight Filter (LWF) or use the Windows Filtering Platform (WFP), depending on the driver’s purpose.


NLB.SYS is a NDIS Lightweight Filter driver (LWF).  When a NDIS 5 IM driver is layered in the same stack, NLB.SYS’ FilterAttachHandler is called twice.  The second call to attach fails, so initializing NLB fails.


After installing a product that uses a NDIS 5.x IM driver when NLB is also installed, network icons disappear and IPconfig does no longer show network adapters.  The Network Load Balancer will record Event IDs 34, 88 and 98 to the System Event Log from “Microsoft-Windows-NLB”.

Note This is a "FAST PUBLISH" article created directly from within the Microsoft support organization. The information contained herein is provided as-is in response to emerging issues. As a result of the speed in making it available, the materials may include typographical errors and may be revised at any time without notice. See Terms of Use for other considerations.

Article ID: 2021976 - Last Review: 12/12/2015 07:26:45 - Revision: 1.0

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