2.1 Describe device virtualization technologies
📘CCNP Encore (350-401-ENCORE-v1.1)
What Is a Virtual Machine (VM)?
A Virtual Machine (VM) is a software-based computer that runs inside another physical computer.
- A VM behaves like a real computer
- It has its own operating system
- It has virtual CPU, memory, storage, and network interfaces
- It runs applications independently
Even though many VMs run on the same physical server, each VM believes it is a separate computer.
Why Virtual Machines Are Used in IT Networks
Virtual machines are used to:
- Run multiple operating systems on one physical server
- Improve hardware utilization
- Reduce costs
- Improve scalability and flexibility
- Isolate applications for security and stability
In enterprise networks, VMs are widely used for:
- Servers
- Network services
- Security appliances
- Testing environments
- Cloud platforms
Relationship Between VMs and Hypervisors
A hypervisor is required to create and manage virtual machines.
Hypervisor Role:
- Allocates CPU, RAM, storage, and network
- Controls VM isolation
- Starts, stops, and monitors VMs
Key Point for Exam:
Virtual machines cannot run without a hypervisor
Components of a Virtual Machine
Each VM includes the following virtual components:
1. Virtual CPU (vCPU)
- A portion of the physical CPU
- Shared among multiple VMs
- Scheduled by the hypervisor
2. Virtual Memory (vRAM)
- Assigned from physical RAM
- Each VM has its own memory space
- Memory isolation prevents one VM from affecting another
3. Virtual Storage
- Stored as files (e.g., VMDK, VHD)
- Appears as a physical hard disk to the VM
- Can be moved, copied, or backed up easily
4. Virtual Network Interface Card (vNIC)
- Allows the VM to connect to networks
- Uses virtual switches
- Supports IP addressing, VLANs, and routing
Virtual Machine Isolation
One of the most important VM features is isolation.
- A problem in one VM does not affect other VMs
- Each VM has:
- Its own OS
- Its own applications
- Its own network identity
Exam Note:
Isolation improves security, stability, and fault tolerance
Virtual Machine Operating Systems
Each VM runs its own operating system, called a guest OS.
Examples:
- Windows Server
- Linux distributions
- Network operating systems
- Security appliances
The physical server OS (if present) is called the host OS.
VM Resource Allocation
The hypervisor controls how resources are assigned.
CPU Allocation:
- Fixed or shared CPU cores
- CPU scheduling ensures fairness
Memory Allocation:
- Static or dynamic memory
- Some hypervisors support memory optimization
Storage Allocation:
- Thin provisioning (use storage as needed)
- Thick provisioning (reserve storage in advance)
Virtual Networking in VMs
VMs use virtual networks, which behave like physical networks.
Virtual Networking Includes:
- Virtual switches
- Virtual NICs
- VLAN support
- IP routing and firewall rules
VMs can:
- Communicate with other VMs
- Communicate with physical devices
- Access external networks
VM Lifecycle Operations (Exam Important)
Common VM operations include:
- Create
- Start
- Stop
- Suspend
- Snapshot
- Clone
- Migrate
Snapshot:
- Saves the VM’s state at a point in time
- Useful for rollback
Live Migration:
- Moves a running VM to another host
- No service interruption
- Important in enterprise environments
Benefits of Virtual Machines
1. Hardware Efficiency
- Multiple VMs share one physical server
- Reduces unused resources
2. Scalability
- Easy to add or remove VMs
- Supports rapid deployment
3. High Availability
- VMs can be restarted on another host
- Used in data center redundancy
4. Simplified Management
- Centralized control
- Automated provisioning
Limitations of Virtual Machines
1. Performance Overhead
- Slightly slower than physical machines
- Depends on hypervisor efficiency
2. Resource Contention
- Too many VMs can overload hardware
3. Licensing Complexity
- OS and software licenses still apply
4. Not Ideal for All Workloads
- Some workloads require direct hardware access
Virtual Machines vs Physical Machines (Exam Comparison)
| Feature | Virtual Machine | Physical Machine |
|---|---|---|
| Hardware | Virtual | Physical |
| Flexibility | High | Low |
| Deployment | Fast | Slow |
| Isolation | Yes | No |
| Scalability | Easy | Difficult |
Virtual Machines in Cisco and Enterprise Networks
In CCNP-level networks, VMs are used for:
- Network controllers
- Management platforms
- Monitoring systems
- Security services
- Automation tools
VMs enable software-defined networking (SDN) and network virtualization.
Key Exam Points to Remember
✔ A VM is a software-based computer
✔ Requires a hypervisor
✔ Has its own OS and resources
✔ Provides isolation and flexibility
✔ Supports snapshots and migration
✔ Widely used in enterprise and cloud networks
Simple One-Line Summary (Exam Ready)
A virtual machine is a software-based system that runs its own operating system and applications using virtualized hardware provided by a hypervisor.
