Firstly, I'll admit that my networking knowledge is limited so as people request more information I'll update this question accordingly.
I am trying to create a NLB Cluster across 2 Windows Server 2008 Web Servers. Neither of the machines are members of a domain, and both have 2 NICs (one for processing external web traffic, and one for communicating internally).
I have installed NLB on both machines, and have created a cluster on Host A and added itself to it. However, when I try and add Host B (using the address from the external NIC) I get the following error : "The RPC server is unavailable on the specified computer".
On Host B I can see that the RPC service is running fine. I can also ping and RDP from Host A to Host B with no problems either. I have disabled the windows firewall on both machines but that had no effect
Best Answer
My guess is your problem is that the two servers are on different domains and you are initiating this from a domain account. If you want to create an NLB between the two servers you must do it from a local administrator account that exists on both servers.
"NLB can have mixed of Domain Controllers, Member Servers, Workgroup servers etc. This is not the limitation of NLB actually. NLB should be able to access the computer using the built-in administrator account."
http://support.microsoft.com/kb/556067