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|Oracle VM Server for SPARC 2.1 Administration Guide Oracle VM Server for SPARC|
A virtual network (vnet) device is a virtual device that is defined in a domain connected to a virtual switch. A virtual network device is managed by the virtual network driver, and it is connected to a virtual network through the hypervisor using logical domain channels (LDCs).
A virtual network device can be used as a network interface with the name vnetn, which can be used like any regular network interface and configured with the ifconfig command .
You can add a virtual network device to a domain, set options for an existing virtual network device, and remove a virtual network device by using the ldm add-vnet, ldm set-vnet, and ldm rm-vnet commands, respectively. For more information, see the ldm(1M) man page.
Figure 8-1 Setting Up a Virtual Network
Following is an explanation for the example in Figure 8-1.
The virtual switch in the service domain is connected to the guest domains. This allows guest domains to communicate with each other.
The virtual switch is also connected to the physical network interface nxge0. This allows guest domains to communicate with the physical network.
The virtual switch network interface vsw0 is created in the service domain, so this allows the two guest domains to communicate with the service domain.
The virtual switch network interface vsw0 in the service domain can be configured using the ifconfig command.
The virtual network interfaces vnet0 in the guest domains can be configured using the ifconfig command.
Basically the virtual switch behaves like a regular physical network switch and switches network packets between the different systems, such as guest domains, service domain, and physical network, to which it is connected.
Until the Oracle VM Server for SPARC 2.1 release, the Logical Domains Manager would assign LDC channels in the following manner:
An LDC channel would be assigned between the virtual network devices and the virtual switch device.
An LDC channel would be assigned between each pair of virtual network devices that are connected to the same virtual switch device (inter-vnet).
The inter-vnet LDC channels are configured so that virtual network devices can communicate directly to achieve high guest-to-guest communications performance. However, as the number of virtual network devices in a virtual switch device increases, the number of required LDC channels for inter-vnet communications increases exponentially.
Starting with the Oracle VM Server for SPARC 2.1 release, you can choose to enable or disable inter-vnet LDC channel allocation for all virtual network devices attached to a given virtual switch device. By disabling this allocation, you can reduce the consumption of LDC channels, which are limited in number.
Disabling this allocation is useful in the following situations:
When guest-to-guest communications performance is not of primary importance
When a large number of virtual network devices are required in a virtual switch device
By not assigning inter-vnet channels, more LDC channels are available for use to add more virtual I/O devices to a guest domain.
Note - If guest-to-guest performance is of higher importance than increasing the number of virtual network devices in the system, do not disable inter-vnet LDC channel allocation.
The following figure shows a typical virtual switch that has three virtual network devices. The inter-vnet-link property is set to on, which means that inter-vnet LDC channels are allocated. The guest-to-guest communications between vnet1 and vnet2 is performed directly without going through the virtual switch.
Figure 8-2 Virtual Switch Configuration That Uses Inter-Vnet Channels
The following figure shows the same virtual switch configuration with the inter-vnet-link property set to off. That means that inter-vnet LDC channels are not allocated. You can see that fewer LDC channels are used than when the inter-vnet-link property is set to on. In this configuration, guest-to-guest communications between vnet1 and vnet2 must go through vsw1.
Note - Disabling the assignment of inter-vnet LDC channels does not prevent guest-to-guest communications. Instead, all guest-to-guest communications traffic goes through the virtual switch rather than directly from one guest domain to another guest domain.
Figure 8-3 Virtual Switch Configuration That Does Not Use Inter-Vnet Channels