A VNIC is a virtualized Network Interface Card, used by a Virtual Machine as its network interface. A VNIC is assigned a MAC address. Each MAC address corresponds with a single virtual NIC, which is used by a virtual machine. You can create a VNIC when you create or edit a virtual machine. There is no real limit to the number of VNICs available to any single virtual machine. Each VNIC must belong to a virtual machine and cannot exist independently of it. This requirement was implemented in version 3.3.1 of Oracle VM. Previous versions allowed you to create VNICs independently of virtual machines and then to assign them as required. This approach was frequently confusing and more difficult to manage.
VNICs are automatically related to a network bridge that is created on the hosting Oracle VM Server. It is possible to configure the network in such a way that virtual machines are able to only interact with each other on the same Oracle VM Server, with all of the virtual machines running across the server pool, or with all of the virtual machines and a public network such as the Internet.
Since MAC addresses need to be unique on a network, Oracle VM Manager dynamically creates MAC addresses to be allocated to each VNIC from a predefined range. Oracle VM Manager attempts to ensure that no two VNICs are able to have the same MAC address. It is possible to modify the MAC address range that Oracle VM Manager uses to allocate for VNICs. This is described in more detail in Virtual NICs in the Oracle VM Manager User's Guide.
Network configuration on a virtual machine can be achieved using the tools available in the guest operating system. If you require DHCP configuration, you equally require a DHCP server to be configured on a network that is attached to the virtual machine network. For this reason, along with the benefit of added security, it is often useful to implement full network separation particularly for the function of the virtual machine network. This can be achieved using VLANs, or separate physical network ports or bonds.
Different network configurations and network separation are discussed in more detail in Chapter 5, Understanding Networks.