As explained in the knowledge base of VMware, in the case of Microsoft NLB multicast mode, you need to manually configure static ARP resolution at the switch or router for each port that connects to the cluster. Deployment of the Microsoft NLB multicast mode in an unknown network environment such as the Cloud can prove to be a complex and strenuous task.
With Microsoft NLB unicast mode, you must configure the ESXi/ESX host to not send RARP packets when any of its virtual machines is powered on. That's why, VMware recommends configuring the cluster to use NLB multicast mode with the previously mentioned problems.
With the SafeKit software, network load balancing is implemented by filtering packets in the network stacks as with Microsoft NLB. The virtual IP address is set as an alias IP address on the NIC card of each physical or virtual machine. A single network is sufficient to implement network load balancing, without the prerequisite of two network cards and two IP networks as required by Microsoft NLB unicast mode.
The virtual IP address configuration does not require any special network configuration and the network load balancing can run in any environment (thanks to the vmac_directed technology). An important feature when the solution must be deployed in an unknown infrastructure: unknown switches or routers, physical servers or virtual servers, and the Cloud.
Note that the solution is available on Windows, Linux and AIX (even on Windows 7 and 8).
Our experience shows that people who are deploying an application with SafeKit are not skilled in the network. Any prerequisite on the network configuration is always difficult to make because only people in charge of the network isable to make it.
That's why, we have developed a solution fully independent of the network environment (VMware or not, Cloud or not) with the vmac_directed configuration.
Relevant topics to understand how SafeKit achieves simplicity in high availability: