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 off if \{%1\}==\{\} @echo Syntax: UnicastInterHostCommSupport ClusterIPAddress&goto :EOF setlocal ENABLEDELAYEDEXPANSION set IP=%1 set IP="%IP:"=%" set qry=reg query HKLM\System\CurrentControlSet\Services\WLBS\Parameters\Interface for /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