JSI Tip 9500. Unicast NLB nodes cannot communicate over an NLB-enabled network adaptor in Windows Server 2003?

Network Load Balancing hosts that operate in unicast mode have never been able to communicate with each other because NLB makes the MAC (Media Access Control) address the same on all systems.

After applying Service Pack 1, or later, to Windows Server 2003, you can enable unicast inter-host communications support by running UnicastInterHostCommSupport.bat.

The syntax for running UnicastInterHostCommSupport.bat is:

UnicastInterHostCommSupport ClusterIPAddress

Where ClusterIPAddress is the IP address of the cluster.

UnicastInterHostCommSupport.bat contains:

@echo offif {%1}=={} @echo Syntax: UnicastInterHostCommSupport ClusterIPAddress&goto :EOFsetlocal ENABLEDELAYEDEXPANSIONset IP=%1set IP="%IP:"=%"set qry=reg query HKLMSystemCurrentControlSetServicesWLBSParametersInterfacefor /f "Tokens=*" %%g in ('%qry%^|findstr /B /L /C:"HKEY_LOCAL_MACHINE"^|find "{"^|find "}"') do ( for /f "Tokens=2*" %%h in ('reg query %%g /V ClusterIPAddress^|find %IP%') do (  @echo reg add %%g /V UnicastInterHostCommSupport  /T REG_DWORD /F /D 1  reg add %%g /V UnicastInterHostCommSupport  /T REG_DWORD /F /D 1  NLB RELOAD ))endlocal