In this configuration, load balancing is based on the number of physical network cards and the number of virtual ports used. With this configuration policy, a virtual network card connected to a vSwitch port will always use the same physical network card. If a physical network card fails, the virtual network card is redirected to another physical network card.

It does a reasonable job of balancing your egress uplinks for the traffic leaving an ESXi host as long as all the VMs using these uplinks have similar usage patterns.

It is important to note that port allocation occurs only when a VM is started or when a failover occurs. Balancing is done based on a port's occupation rate at the time the VM starts up. This means that which pNIC is selected for use by this VM is determined at the time the VM powers on, based on which ports in the vSwitch are occupied at the time. For example, if you start 20 VMs in a row on a vSwitch with two pNICs, the odd-numbered VMs would use the first pNIC and the even-numbered VMs would use the second pNIC, and this would persist even if you shut down all the even-numbered VMs; the first pNIC would have all the VMs and the second pNIC would have none. It might happen that two heavily loaded VMs are connected to the same pNIC; if this happens, load would not be balanced.

This policy is the easiest one, and we always call for the simplest one to map it to a best operational simplification.

Now when speaking of this policy, it is important to understand that if, for example, teaming is created with two 1 GB cards and if one VM consumes more than one card's capacity, a performance problem will arise because traffic greater than 1 Gbps will not go through the other card and there will be an impact on the VMs sharing the same port as the VM consuming all the resources. Likewise, if two VMs each wish to use 600 Mbps and they happen to go to the first pNIC, the first pNIC will not be able to meet the 1.2 Gbps demand, no matter how idle the second pNIC is.