A virtualized server might contain multiple virtual NICs over the same physical link. You can assign these VNICs to VMs. Traditionally, a switch does not transmit packets back on the same link on which it receive the packets. Packets between VMs are looped back by the virtual switch within the host itself. Therefore, any policies that are configured on the external switch are not applied to inter-VM packets. With the support for EVB, Oracle Solaris and the switch enable inter-VM packets to be switched by the external switch after enforcing any policies on the inter-VM packets. For more information about VNICs, see Chapter 2, Creating and Managing Virtual Networks.
In addition, Oracle Solaris with the support of EVB can exchange information about VNICs with the switch. This exchange of information enables the switch to automatically configure the VNIC properties such as bandwidth limits, bandwidth shares, and MTU on the network. In the absence of this feature, the server administrator and the network administrator must coordinate with each other to make changes on the switch every time a VNIC is created, modified, or deleted on the server. Extending the VNIC properties into the network leads to an efficient use of networking resources based on VNIC properties. For example, enforcing a bandwidth limit on packets after they arrive at the host is not very helpful because the packets might have already used up the link bandwidth.