Virtual Interface Management

Virtual Circuits

A virtual circuit or virtual path refers to the path that a frame takes from its source vNIC to its destination virtual switch port (vEth) or from a source virtual switch port to its destination vNIC. There are many possible virtual circuits that traverse through a physical cable. Cisco UCS Manager uses virtual network tags (VN-TAG) to identify these virtual circuits and differentiate between them. The OS decides the virtual circuit that a frame must traverse on a basis of a series of decisions.

In the server, the OS decides the Ethernet interface from which to send the frame.


Note

During service profile configuration, you can select the fabric interconnect to be associated with a vNIC. You can also choose whether fabric failover is enabled for the vNIC. If fabric failover is enabled, the vNIC can access the second fabric interconnect when the default fabric interconnect is unavailable. Cisco UCS Manager Server Management Guide provides more details about vNIC configuration during service profile creation.

After the host vNIC is selected, the frame exits the selected vNIC and, through the host interface port (HIF), enters the IOM to which the vNIC is pinned. The frame is then forwarded to the corresponding network Interface port (NIF) and then to the Fabric Interconnect to which the IOM is pinned.

The NIF is selected based on the number of physical connections between the IOM and the Fabric Interconnect, and on the server ID from which the frame originated.

Virtual Interfaces

In a blade server environment, the number of vNICs and vHBAs configurable for a service profile is determined by adapter capability and the amount of virtual interface (VIF) namespace available on the adapter. In Cisco UCS, portions of VIF namespace are allotted in chunks called VIFs. Depending on your hardware, the maximum number of VIFs are allocated on a predefined, per-port basis.

The maximum number of VIFs varies based on hardware capability and port connectivity. For each configured vNIC or vHBA, one or two VIFs are allocated. Stand-alone vNICs and vHBAs use one VIF and failover vNICs and vHBAs use two.

The following variables affect the number of VIFs available to a blade server, and therefore, how many vNICs and vHBAs you can configure for a service profile.

  • Maximum number of VIFs supported on your fabric interconnect

  • How the fabric interconnects are cabled

  • If your fabric interconnect and IOM are configured in fabric port channel mode

For more information about the maximum number of VIFs supported by your hardware configuration, see the appropriate Cisco UCS Configuration Limits for Cisco UCS Manager for your software release.

Virtual Interface Subscription Management and Error Handling

For fabric interconnects grouped in a port-channel, changes to the way you connect the fabric interconnect to the I/O module could result in a drastic change to the number of VIFs available to a blade server. To help you track the effect of these changes, Cisco UCS Manager maintains the following metrics:

  • Maximum number of VIFs supported by hardware

  • Connectivity type

If you change your configuration in a way that decreases the number of VIFs available to a blade, UCS Manager will display a warning and ask you if you want to proceed. This includes several scenarios, including times where adding or moving a connection decreases the number of VIFs.

Virtualization in Cisco UCS

Overview of Virtualization

Virtualization allows you to create multiple Virtual Machines (VMs) to run in isolation, side by side on the same physical machine.

Each virtual machine has its own set of virtual hardware (RAM, CPU, NIC) upon which an operating system and fully configured applications are loaded. The operating system sees a consistent, normalized set of hardware regardless of the actual physical hardware components.

In a virtual machine, both hardware and software are encapsulated in a single file for rapid provisioning and moving between physical servers. You can move a virtual machine, within seconds, from one physical server to another for zero-downtime maintenance and continuous workload consolidation.

The virtual hardware makes it possible for many servers, each running in an independent virtual machine, to run on a single physical server. The advantages of virtualization include better use of computing resources, greater server density, and seamless server migration.

Overview of Cisco Virtual Machine Fabric Extender

A virtualized server implementation consists of one or more VMs that run as guests on a single physical server. The guest VMs are hosted and managed by a software layer called the hypervisor or virtual machine manager (VMM). Typically, the hypervisor presents a virtual network interface to each VM and performs Layer 2 switching of traffic from a VM to other local VMs or to another interface to the external network.

Working with a Cisco virtual interface card (VIC) adapter, the Cisco Virtual Machine Fabric Extender (VM-FEX) bypasses software-based switching of VM traffic by the hypervisor for external hardware-based switching in the fabric interconnect. This method reduces the load on the server CPU, provides faster switching, and enables you to apply a rich set of network management features to local and remote traffic.

VM-FEX extends the IEEE 802.1Qbh port extender architecture to the VMs by providing each VM interface with a virtual Peripheral Component Interconnect Express (PCIe) device and a virtual port on a switch. This solution allows precise rate limiting and quality of service (QoS) guarantees on the VM interface.


Important

VM-FEX is not supported with Cisco UCS 6454 Fabric Interconnects.

Virtualization with Network Interface Cards and Converged Network Adapters

Network interface card (NIC) and converged network adapters support virtualized environments with the standard VMware integration with ESX installed on the server and all virtual machine management performed through the VC.

Portability of Virtual Machines

If you implement service profiles you retain the ability to easily move a server identity from one server to another. After you image the new server, the ESX treats that server as if it were the original.

Communication between Virtual Machines on the Same Server

These adapters implement the standard communications between virtual machines on the same server. If an ESX host includes multiple virtual machines, all communications must go through the virtual switch on the server.

If the system uses the native VMware drivers, the virtual switch is out of the network administrator's domain and is not subject to any network policies. As a result, for example, QoS policies on the network are not applied to any data packets traveling from VM1 to VM2 through the virtual switch.

If the system includes another virtual switch, such as the Nexus 1000, that virtual switch is subject to the network policies configured on that switch by the network administrator.

Virtualization with a Virtual Interface Card Adapter

A Cisco VIC adapter is a converged network adapter (CNA) that is designed for both bare metal and VM-based deployments. The VIC adapter supports static or dynamic virtualized interfaces, which includes up to 116 virtual network interface cards (vNICs).

There are two types of vNICs used with the VIC adapter—static and dynamic. A static vNIC is a device that is visible to the OS or hypervisor. Dynamic vNICs are used for VM-FEX by which a VM is connected to a veth port on the Fabric Interconnect.

VIC adapters support VM-FEX to provide hardware-based switching of traffic to and from virtual machine interfaces.