VLANs in VMware Infrastructure
VLANs provide for logical groupings of stations or switch ports, allowing communications as if all stations or ports were on the same physical LAN segment. Confining broadcast traffic to a subset of the switch ports or end users saves significant amounts of network bandwidth and processor time.
In order to support VLANs for VMware Infrastructure users, one of the elements on the virtual or physical network has to tag the Ethernet frames with 802.1Q tag, as shown in Figure 3. There are three different configuration modes to tag (and untag) the packets for virtual machine frames.
• Virtual switch tagging (VST mode) — This is the most common configuration. In this mode, you provision one port group on a virtual switch for each VLAN, then attach the virtual machine’s virtual adapter to the port group instead of the virtual switch directly. The virtual switch port group tags all outbound frames and removes tags for all inbound frames. It also ensures that frames on one VLAN do not leak into a different VLAN.
Use of this mode requires that the physical switch provide a trunk.
Virtual machine guest tagging (VGT mode) — You may install an 802.1Q VLAN trunking driver inside the virtual machine, and tags will be preserved between the virtual machine networking stack and external switch when frames are passed from or to virtual switches. The format for the header of a packet tagged in this way is shown in Figure 3.
Use of this mode requires that the physical switch provide a trunk.
• External switch tagging (EST mode) — You may use external switches for VLAN tagging. This is similar to a physical network, and VLAN configuration is normally transparent to each individual physical server.
There is no need to provide a trunk in these environments.
For details on using VLANs with VMware Infrastructure, see the white paper titled VMware ESX Server 3 802.1Q VLAN Solutions, available from the VMTN Web site (http://www.vmware.com/vmtn/).
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