VMware Server Virtual Network Architecture
Just as with physical networks, the VMware virtual networking architecture is comprised of multiple components which can be configured in different ways to achieve a variety of network configurations. A physical network consists of both software (for example a DHCP server) and hardware devices such as network adapters and switches. The key difference between a physical network and a virtual network is that in a virtual network the hardware devices are represented in software within the virtualizaion environment.
The object of this chapter of VMware Server 2.0 Essentials is to provide an overview of the various components which combine make up virtual networks within a VMware Server 2.0 based environment.
VMware Server Virtual Network Switch
In a physical network configuration, a switch is typically a hardware device which is used to provide a central point of network connectivity for network clients. The devices on a network connected to a switch using twisted pair cabling. When a client sends a network packet to another device on the network, the switch checks the packet for the MAC address of the destination device and fowards the packet to the port to which that device is connected.
VMware Server includes a virtual network switch which. although entirely software based, performs the same task as physical switch, in that it allows virtual devices, such as virtual machines and other virtual network components, to be connected together to form a virtual network. According to VMware, Inc., VMware Server 2.0 supports a total of 10 virtual switches on Windows hosts and 255 on Linux hosts. In addition, while virtual switches on Windows hosts can have an unlimited number of ports, Linux based switches are limited to 32 ports per switch.
Virtual switches are used in Bridged, NAT and HostOnly virtual network configurations, under which the virtual switches are named vmnet0, vmnet1 and vmnet8 respectively. Additional virtual switches may be added, up to the allowed host platform maximum, using the names vmnet2, vmnet3 etc.
A list of currently configured network, and switches to which they are assigned may viewed via the VI Web Access management interface, by selecting the host system from the Inventory panel and locating the Networks panel in the Summary workspace. The following figure illustrates the Networks panel with three virtual switches configured:
In the the above example, there are three networks named Bridged, HostOnly and NAT. These are assigned to virtual switches vmnet0, vmnet1 and vmnet8 respectively.
The switches available by default are the result of choices made during the initial VMware Server installation and configuration process as described in the Installing VMware Server 2.0 on Linux Systems and Installing VMware Server 2.0 on Windows Systems chapters of this book. if, for example, vmnet8 is not listed this is most likely due to the fact that NAT was not selected as a network configuration option during the VMware Server installation.
To identify the switch to which a particular virtual machine is connected, select the machine from the Inventory and refer to the Hardware panel of the Summary page. Any Network Adapter entries will list the name of the network to which that virtual network adapter is connected, which may then be cross referenced with the host information obtained above to identify the corresponding virtual switch (in this case vmnet0).
