Cisco®CCDA Exam Cram Notes : Concepts Of Virtualization Within A Network Design

4. Considerations for Expanding an Existing Network

4.2 Describe the concepts of virtualization within a network design

Physical elements (chassis, VSS, VDC, contexts): Virtual Device Contexts (VDCs): The Nexus 7000 NX-OS software supports Virtual Device Contexts (VDCs), VDC(s) allow the partitioning of a single physical Nexus 7000 device into multiple logical devices.

This logical separation provides the following benefits:

  • Administrative and management separation
  • Change and failure domain isolation from other VDCs
  • Address, VLAN, VRF, and VPC isolation

VPC and VSS: Both are used basically to support multi-chassis ether-channel that means we can create a port-channel whose one end is device A,however, another end is physically connected to 2 different physical switches which logically appears to be one switch.

VPC and VSS

The main differences between VPC and VSS are as below:

  • VPC is Nexus switch specific feature, however,VSS is created using 6500 series switches
  • Once switches are configured in VSS, they get merged logicaly and become one logical switch from control plane point of view that means single control plane is controlling both the switches in active standby manner, however, when we put nexus switches into VPC, their control plane are still separate.
  • In VSS, only one logical switch has be managed from management and configuration point of view. That means, when the switches are put into VSS, now, there is only one IP which is used to access the switch.

Virtual Routing and Forwarding (VRF) creates multiple logical Layer 3 route tables that can function on the same physical router

VDC Virtual Device Context - VDC allows the switches to be virtualized at the device level. Each configured VDC presents itself as a unique device to connected users within the framework of that physical switch. The VDC runs as a separate logical entity within the switch, maintaining its own unique set of running software processes, having its own configuration, and being managed by a separate administrator.

The Cisco Nexus 7000 Series Switches introduce support for the Cisco NX-OS Software platform, a new class of operating system designed for data centers. Based on the Cisco MDS 9000 SAN-OS platform, Cisco NX-OS introduces support for virtual device contexts (VDCs).

The following are true about virtualization technology

1. Virtual Switching System (VSS) allows two physical Cisco Catalyst 6500 series switches to act as a single logical virtual switch.

2. Virtual routing and forwarding (VRF) creates multiple logical Layer 3 routing and forwarding instances (route tables) that can function on the same physical router.

3. Virtual PortChannel (vPC) technology may be used to combine two Cisco Nexus 7000 series switches with 10GE links, which are then represented to other switches as a single logical switch for port channeling purposes.

4. Device contexts enable a single physical network device to host multiple virtual network devices.

Typical enterprise data centers contain a huge number of servers. Many of these servers sit idle as the workload is distributed to only some of the servers on the network. This results in a waste of expensive hardware resources, power, maintenance and cooling requirements. Server virtualization attempts to increase resource utilization by partitioning physical servers into several multiple virtual servers, each running its own operating system and applications. Server virtualization makes each virtual server look and act like a physical server, multiplying the capacity of every single physical machine.

The concept of server virtualization is widely applied in IT infrastructure as a way of minimizing costs by increasing the utilization of existing resources. Virtualizing servers is often a good solution for small- to medium-scale applications. This technology is widely used for providing cost-effective web hosting services.

Some of the virtual servers and manufacturers are given below:

a. VMware ESX Server

b. Citrix XenServer

c. Microsoft Hyper-V

Components of data center 3.0

Virtualization: Virtual local-area network (VLAN), virtual storage-area network (VSAN), and virtual device contexts (VDC) help to segment the LAN, SAN, and network devices instances.

Unified fabric: Virtual local-area network (VLAN), virtual storage-area network (VSAN), and virtual device contexts (VDC) help to segment the LAN, SAN, and network devices instances.

Unified computing: The Cisco Unified Computing SystemTM is unites compute, network, storage access, and virtualization into a cohesive system. The system integrates a low-latency, lossless 10 Gigabit Ethernet unified network fabric with enterprise-class, x86-architecture servers.

Logical elements (routing elements, tunneling, VRFs, VLANs):

VLAN: A VLAN is a group of devices on one or more logically segmented LANs. All devices working on a VLAN will have same broadcast domain. Like routers, switches (Layer 2) have the ability to provide domain broadcast segmentation called a VLAN. Using VLAN technology, you can group switch ports and their connected users into logically defined communities of interest. A VLAN operating on a Catalyst switch limits transmission of unicast, multicast, and broadcast traffic to only the other ports belonging to that VLAN, thereby controlling broadcasts.

A VLAN belongs to a specific network number. To move traffic from one VLAN (one broadcast domain) to another VLAN (another broadcast domain) a router is required.

Access layer protection includes private VLANs, port security, DHCP snooping, IPSource Guard, secure Address Resolution Protocol (ARP) detection, and dynamic ARP inspection. These features protect the network against attacks such as man-in-the-middle, spoofing, and infrastructure denial-of-service (DoS) attacks.

VRF: Stands for Virtual Routing and Forwarding is a technology that allows multiple instances of a routing table to co-exist within the same router at the same time.

VPC: A virtual PortChannel (vPC) allows links that are physically connected to two different Cisco Nexus 5000 Series devices to appear as a single PortChannel to a third device. The third device can be a Cisco Nexus 2000 Series Fabric Extender or a switch, server, or any other networking device. A vPC can provide Layer 2 multipathing, which allows you to create redundancy by increasing bandwidth, enabling multiple parallel paths between nodes and load-balancing traffic where alternative paths exist.

VSS: A Virtual Switching System is network system virtualization technology that pools multiple Cisco Catalyst 6500 Series Switches into one virtual switch, increasing operational efficiency, boosting nonstop communications, and scaling system bandwidth capacity to 1.4 Tbps. For example, VSS will allow two physical Cisco Catalyst 6500 Series Switches to operate as a single logical virtual switch called a virtual switching system

VDC: A Virtual Device Context allows the switches to be virtualized at the device level. Each configured VDC presents itself as a unique device to connected users within the framework of that physical switch. The VDC runs as a separate logical entity within the switch, maintaining its own unique set of running software processes, having its own configuration, and being managed by a separate administrator.

The Cisco Nexus 7000 Series Switches introduce support for the Cisco NX-OS Software platform, a new class of operating system designed for data centers. Based on the Cisco MDS 9000 SAN-OS platform, Cisco NX-OS introduces support for virtual device contexts (VDCs).

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