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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. In order to fully appreciate how the VMware Server virtual network architecture fits together it is first necessary to understand the concepts of ''Virtual Network Switches'', ''Virtual Network Adapters'', ''Host Virtual Adapters'' and ''DHCP'' and ''NAT'' servers, each of which will be covered in detail in this chapter.
== 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 forwards 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.
== VMware Server 2.0 Virtual Network Adapter (NIC) ==
In order to communicate with the virtual network configurationnetworks, virtual machines need at least one virtual network adapter. Although these are software components running the the VMware Server environment, they appear as physical hardware devices to the guest operating systems, specifically an AMD PCNet adapter on 32-bit guest operating systems, and an Intel Pro/1000 MT adapter for 64-bit and Windows Vista guests. In each of the network configuration modes (Bridged, HostOnly and NAT), the virtual network adapters connect to a ''virtual network switch'', which in turn connects to other network components such as the ''host network adapteradapters'', or ''host virtual adapters'' and a DHCP or ''NAT '' and ''DHCP'' server. With VMware Server 2 it is possible to configure up to 10 virtual network adapters into a single virtual machine. == Host Virtual Adapter == Host virtual adapters are installed on the host operating system and serve to provide communication between the host and any virtual machines in ''NAT'' and ''HostOnly'' virtual network configurations. Two host virtual adapters are installed by VMware Server, one for communication with the NAT virtual network and the second for communication with the HostOnly virtual network. Host virtual adapters are not, by default, connected to any physical network adapter devices on the host system, thereby allowing access solely to the internal virtual networks.
== VMware Server DHCP Server ==
