Network Virtualization - Virtual Switches
What is Virtualization?
Virtualization is the process of creating an abstract hardware layer over the physical hardware.
When is Network Virtualization Used?
Where the traditional server model requires a one to one relationship between physical hardware and the operating system a virtualized model allows for many virtual instances of the abstract hardware layer to be presented so that many operating systems can be installed on the one physical machine. These virtual instances are known as virtual machines.
As the number of virtual machines on the one physical host increases, the network communication demands between the virtual machines also increase. In order to address these demands, vendors such as Cisco Systems and VMware have created network virtualization components to share the resources of the physical host. The Cisco Systems virtual switch offering is a Nexus 1000V, this switch adds functionality to the VMware virtual .switch as well as a more familiar management interface for those with Cisco IOS backgrounds.
Virtual switches provide a virtual network within the physical host so that if virtual machines need to communicate with each other they can do so without traversing the physical network cards and a physical switch.
Virtualization Diagrams
Figure 1. Illustrates a number of virtual machines connected to a virtual switch. The connections are via virtual nics (Virtual Network Interface Cards) and are usually represented with a preceding letter 'V'. For example veth0 stands for virtual Ethernet port 0.
Figure 2. All virtual devices on the physical host have been installed over an abstract hardware layer. In the case of the Virtual machines, the hardware layer emulates x86-compliant server hardware. In the case of the Virtual switch, the hardware layer emulates an Ethernet switch. Over the top of these hardware emulations, operating systems are installed. The operating systems interact with the virtual hardware as if it were physical hardware.
Virtual Network Switch Considerations
Resource Sharing. Sharing physical resources is more efficient because there is very little waste of unused memory or CPU clock cycles. In terms of network virtualization sharing CPU cycles between the Virtual Machines and the Virtual Switch can lead to higher CPU utilization. A busy VM (Virtual Machine) not only requires CPU cycles for the PC/Server operating system, but it can also indirectly cause higher CPU requirements because of the additional work that the virtual switch is required to complete. Virtual switches require CPU cycles to complete packet (Layer 2 frames) switching operations between the virtual ports and the uplink ports.
MAC Address Tables. Virtual Switches do not learn MAC addresses like a normal physical switch. They populate their TCAM tables by adding the MAC address of the virtual machine that is associated with the vethernet port. Virtual switches do also support VLANS and 802.1q trunking, network administrators should ensure that the correct VLANs are configured in the virtual switch.
Virtual Device Manager. VMware virtual switches use a concept of a Virtual Device Manager, this VM is used to configure virtual switches that cannot be managed directly. Cisco Nexus virtual switches are managed by a VSM (virtual switch management) device. Virtual switches can continue to forward packets without an available virtual device manager, however, they cannot be configured without this device. Therefore the network virtualization design should cater for redundant virtual device managers and suitable backups of these VMs.
Shared Storage. A crucial component of virtual machines is shared storage. Virtual machines, their operating systems and the data on the operating systems are all stored on shared storage. This allows the VM the flexibility to move between physical hosts provided that the hosts have access to the same physical storage. The virtual device manager is presented on a virtual machine and therefore enjoys the same benefits as other VMs and suffers the same constraints as other VMs.
Virtual Network Organizational Role Considerations
Unlike other types of virtual network technologies such as VLANs, VPNs and VRFs, virtual networks blur the lines between the traditional network administrator and the virtualization teams. The configuration of VLANs and switchports traditionally belonged in the networks teams, however, by virtue of using a virtual device manager to configure the virtual switches a traditional networking task now requires virtualization skills.
This problem is aleviated with the introduction of the Nexus 1000V by Cisco systems. Although the configuration is still reliant of a virtual device manager, the Nexus provides a traditional IOS look and feel to the configuration allowing the network team to create port profiles that can then be used by VM administrators without requiring any more knowledge of the network.
Custom Search
