Question : Virtual IP address on Win2003 Network Load Balancing (NLB) not available across VLANs/switch

Dear Experts,

We have just installed 2 new servers -serverA and serverB.  They are both running Win2003 Server standard with all latest patches etc.  We have installed the NLB component and configured as per MS's online documentation.  The aim is that they will recieve http requests from internal and external clients.  The servers are located on a subnet defined as a separate VLAN on our stacked Cisco 3750s.  All servers are located on the same VLAN.  All workstations are located on a separate VLAN/subnet on the same stacked 4 x 3750s.

The problem is that the virtual IP address of the NLB "cluster" is not contactable from any other VLANs.  Within the server VLAN, it is possible to connect to the virtual IP and access the web page hosted on the boxes.  No clients on the workstation VLAN (or any other location) can access the NLB cluster address and it is not pingable either.  It is as if the switch is not aware of the virtual address.

We have a little networking knowledge but not enough it seems.  We logged onto the switches and did "show arp" command and saw the address was not listed.  Do we need to add a static ARP address perhaps?  I should add that we already have a separate "true" MS Cluster running on the server VLAN, with which we had no problem with.

Any ideas would be great - thanks!

Answer : Virtual IP address on Win2003 Network Load Balancing (NLB) not available across VLANs/switch

You're running the NLB cluster in multicast mode; in this case, you'll indeed have to create static ARP entries to access the clustered IP address from another subnet.
Other than that, if you have two NICs in each machine, you can run the cluster in unicast mode without losing inter-cluster communication.

Network Load Balancing Frequently Asked Questions
http://www.microsoft.com/technet/prodtechnol/windowsserver2003/technologies/clustering/nlbfaq.mspx

Network Load Balancing: Configuration Best Practices for Windows 2000 and Windows Server 2003
http://www.microsoft.com/technet/prodtechnol/windowsserver2003/technologies/clustering/nlbbp.mspx