Microsoft Network Load Balancing (NLB) on VMware ESX
The other day I went into a Microsoft Network Load Balancing issue. The customer had configured a Microsoft NLB cluster in Unicast mode with 4 nodes (VMs) in a ESX farm. One could say it works out of the box, just go for the default configuration and voila. Well not true in that particular ESX and physical network environments.
So let me explain the 2 main cast modes when deploying a NLB cluster:
- UNICAST mode
- MULTICAST mode (prefered)
Here are the following steps to configure NLB in MULTICATS mode:
- Install Microsoft NLB and set MULTICAST mode (more at VMware KB 1006558)
- Disable DDNS/WINS. Network Load Balancing does not support dynamic Domain Name System (DNS) resolution, where the name of the cluster is automatically registered by the host when the host starts. This functionality must be disabled on the Network Load Balancing interface for both DNS and Windows Internet Name Service (WINS); otherwise, each host’s computer name will be registered with the cluster IP address. When using Network Load Balancing with DNS, you will need to directly configure the DNS server to register the name.
- Add a static ARP entry in your default router (more at VMware KB 1006525)
- Turn on MULTICAST support on your physical switches. If your switches do not support MULTICAST, you will have to setup Microsoft NLB in UNICAST mode.