Network Load Balancing – NLB – also known as Windows Load Balancing – WLB – has always been a little like living on the edge. It does the job but you are always wondering when and where the next issue is going to come from and what will you need to do to fix it pronto. We have had that issue a number of times in the last 6 months from a variety of causes, some even seeming unrelated changes messing everything up.
Our existing pool of TS Servers has 8 machines in it, using Multicast with IGMP to stay converged. This means loads of traffic everywhere and isn’t the most-recommended solution. So as part of the pre-testing for the Virtualisation, we have P2V’ed the Terminal Servers into a Virtual Sandbox and then created 2 NICs for the VMs and changed them to Unicast mode.
Boom… the WLBS query command showed them as Converged but the GUI management tool wasn’t able to add them. Considering we need the GUI for some of our lesser-skilled staff, we were racking our brains to work it out.. eventually, the light-Bulb went on.
Turns out in creating the VM’s, the automatic DNS registration was left on and the NIC designated as the NLB NIC (as opposed to the Management NIC) was being added to DNS. With the NLB IP being used by DNS, the TS Servers cannot communicate amongst themselves (hence the management NIC) and could not load the NLB GUI Tool.
All I had to do was uncheck the Register this connection’s Addresses in DNS checkbox (as shown on the left – taken from the production pool, not the test one) and then do an ipconfig /flushdns on the TS boxes and it was all good.
Now that this works, we are ready to go live on our Virtual TS pool for all. A simple problem but one that wasn’t readily obvious to us as we were all focusing on the NLB hosts and the Unicast/Multicast.
After I fixed it, I did a search on all the instructions and fault-finding stuff that I usually check and not one mentioned it as a potential “gotcha”. Either we were really unlucky or it is something that is just presumed…
So, if you you come across the same issue, those of you that are still using Windows 2003 NLB, check the DNS of your Terminal Servers.