A few concepts are essential for a thorough understanding of virtual networking. If you are new to ESX, it is helpful to review these concepts.

A physical network is a network of physical machines that are connected so that they can send data to and receive data from each other. VMware ESX runs on a physical machine.

A virtual network is a network of virtual machines running on a single physical machine that are connected logically to each other so that they can send data to and receive data from each other. Virtual machines can be connected to the virtual networks that you create when you add a network.

A physical Ethernet switch manages network traffic between machines on the physical network. A switch has multiple ports, each of which can be connected to a single machine or another switch on the network. Each port can be configured to behave in certain ways depending on the needs of the machine connected to it. The switch learns which hosts are connected to which of its ports and uses that information to forward traffic to the correct physical machines. Switches are the core of a physical network. Multiple switches can be connected together to form larger networks.

A virtual switch, vSwitch, works much like a physical Ethernet switch. It detects which virtual machines are logically connected to each of its virtual ports and uses that information to forward traffic to the correct virtual machines. A vSwitch can be connected to physical switches by using physical Ethernet adapters, also referred to as uplink adapters, to join virtual networks with physical networks. This type of connection is similar to connecting physical switches together to create a larger network. Even though a vSwitch works much like a physical switch, it does not have some of the advanced functionality of a physical switch.

A vNetwork Distributed Switch acts as a single vSwitch across all associated hosts on a datacenter. This allows virtual machines to maintain consistent network configuration as they migrate across multiple hosts.

A dvPort is a port on a vNetwork Distributed Switch that connects to a host’s service console or VMkernel or to a virtual machine’s network adapter.

A port group specifies port configuration options such as bandwidth limitations and VLAN tagging policies for each member port. Network services connect to vSwitches through port groups. Port groups define how a connection is made through the vSwitch to the network. Typically, a single vSwitch is associated with one or more port groups.

A dvPort group is a port group associated with a vNetwork Distributed Switch and specifies port configuration options for each member port. dvPort Groups define how a connection is made through the vNetwork Distributed Switch to the network.

NIC teaming occurs when multiple uplink adapters are associated with a single vSwitch to form a team. A team can either share the load of traffic between physical and virtual networks among some or all of its members, or provide passive failover in the event of a hardware failure or a network outage.

VLANs enable a single physical LAN segment to be further segmented so that groups of ports are isolated from one another as if they were on physically different segments. The standard is 802.1Q.

The VMkernel TCP/IP networking stack supports iSCSI, NFS, and vMotion. Virtual machines run their own systems’ TCP/IP stacks and connect to the VMkernel at the Ethernet level through virtual switches.

IP storage refers to any form of storage that uses TCP/IP network communication as its foundation. iSCSI can be used as a virtual machine datastore, and NFS can be used as a virtual machine datastore and for direct mounting of .ISO files, which are presented as CD-ROMs to virtual machines.

TCP Segmentation Offload, TSO, allows a TCP/IP stack to emit very large frames (up to 64KB) even though the maximum transmission unit (MTU) of the interface is smaller. The network adapter then separates the large frame into MTU-sized frames and prepends an adjusted copy of the initial TCP/IP headers.

Migration with vMotion enables a virtual machine that is powered on to be transferred from one ESX host to another without shutting down the virtual machine. The optional vMotion feature requires its own license key.