A virtual network is a type of logical network that allows devices and services to communicate with each other without being physically connected. A virtual network is created through software-based techniques, enabling a more flexible and efficient use of resources. In a virtual network, multiple devices or services can be connected and managed independently, allowing for better security, isolation, and performance. Virtual networks can be implemented using technologies such as virtual local area networks (VLANs), virtual extensible local area networks (VXLANs), or software-defined networking (SDN).

A virtual machine (VM) is a software-based representation of a physical computer, that can run an operating system and applications, while sharing the resources of a physical host computer. VMs enable efficient use of computing resources, as multiple VMs can run on a single physical host. A hypervisor or virtual machine monitor (VMM) manages the allocation of resources to the VMs and isolates them (memory, CPU, storage, etc.) from one another, ensuring that they function independently. VMs can be used in networking scenarios to host network services, isolate network environments, or run network simulations and testing.

Network Functions Virtualization (NFV) is the process of abstracting network functions, such as routing, firewalls, load balancing, or WAN optimization, from dedicated hardware appliances to run on virtual machines. NFV enables the deployment of these services dynamically and on-demand, improving scalability, and reducing the need for dedicated hardware. It simplifies network management, reduces costs, and increases flexibility. NFV can be used in combination with software-defined networking (SDN) to provide end-to-end control and optimization of the network infrastructure.

Network virtualization tools are software applications or platforms that enable the creation, management, and monitoring of virtual networks and related components. These tools can range from hypervisors, such as VMware ESXi or Microsoft Hyper-V, which manage virtual machines and their resources, to SDN controllers, such as OpenDaylight or ONOS, which provide control over the network's traffic flow and resource allocations. Additionally, network virtualization tools may include network simulators, monitoring tools, or configuration management tools, all of which assist in the deployment and management of virtual networks and their components, helping to optimize performance, security, and reliability.

Software-Defined Networking (SDN) is an approach to networking that centralizes the control plane, thereby enabling network administrators to manage and control the network through software applications. This is in contrast to traditional networks where the control plane is distributed across multiple devices. SDN separates the forwarding plane (data forwarding) and the control plane (decision-making) of the network. This separation allows for a more agile and flexible network with improved management, automation, and orchestration capabilities. SDN controllers serve as the brain of the network, providing an interface for administrators to program and configure the network. By leveraging this centralized control, network administrators can quickly respond to changing business needs and dynamically provision network resources.

Virtual LANs (VLANs) are logical subnets created within a physical network, allowing the segregation of network traffic without the need for separate physical switches or routers. VLANs provide improved network security, traffic management, and resource allocation by allowing administrators to group devices, users, or applications on the same LAN into distinct broadcast domains. This facilitates better control over network traffic, reduces the chance of network congestion, and improves overall network efficiency. VLANs can span multiple switches, enabling network administrators to efficiently allocate resources, manage network growth, and enforce security policies based on organizational requirements. VLANs are typically created and managed using VLAN tagging, where unique tags are appended to network packets to identify their corresponding VLANs.

Virtual Routing and Forwarding (VRF) is a technology that allows multiple instances of routing tables to coexist in a single router. Each instance of VRF can have its own set of routes, interfaces, and routing protocols, providing complete network segmentation and isolation between virtual environments. This is particularly useful for multi-tenant environments, such as data centers and service providers, where each customer must have their own isolated routing domain within the shared infrastructure. VRF enhances security by preventing data leakage and network visibility between unrelated networks. It also improves scalability by allowing network administrators to easily expand their infrastructure to accommodate new customers or services without affecting existing routing configurations.

Overlay networks are virtual networks that are built on top of a physical network using software-defined tunneling protocols. These networks abstract the underlying physical infrastructure and allow for the creation of flexible, scalable, and programmable virtual network topologies that can span multiple data centers or cloud providers. Overlay networks use encapsulation to transport virtual network packets within the underlying physical network packets, thereby allowing the virtual network to operate independently of the physical network's topology or configurations. Common examples of overlay networking technologies include Virtual Extensible LAN (VXLAN) and Network Virtualization using Generic Routing Encapsulation (NVGRE). Overlay networks enable network administrators to simplify complex networking structures, improve resource utilization, and efficiently manage network resources in modern cloud and data center environments.

Virtual Network Services (VNS) are network services typically provided by physical appliances, such as firewalls, intrusion prevention systems, load balancers, and wide area network (WAN) optimization devices, that have been virtualized and are deployed as virtual appliances or software instances. By decoupling these services from the underlying hardware, network administrators can achieve greater flexibility, scalability, and cost savings. Virtual network services can be deployed on-demand, typically through an orchestration platform, and can be easily scaled up or down based on dynamic requirements. This leads to better resource utilization and easier management of network infrastructure. Additionally, VNS can be incorporated into other virtualization software, such as Network Functions Virtualization (NFV) or Software-Defined Networking (SDN), to provide integrated and automated network solutions tailored to the specific needs of an organization.

Virtual switches, also known as vSwitches or virtual network switches, are software-based network devices that manage and control the traffic between virtual machines (VMs) and physical network devices. They function similarly to physical switches but provide added flexibility and scalability. Virtual switches facilitate communication and data transfer between VMs by using network virtualization techniques to create isolated, logical network connections. They also offer advanced management features such as traffic shaping, VLAN tagging, and Quality of Service (QoS) to optimize and prioritize network traffic between VMs.

Virtual Network Adapters, also known as virtual NICs, provide connectivity for virtual machines within a virtualized environment. These software-based network interface cards enable the VM to communicate with physical or virtual network resources. Virtual network adapters help maintain separate IP configurations for each VM, ensuring efficient resource allocation and flexibility within the network. They support various virtualization features such as VLANs, network segmentation, and network traffic management. Additionally, virtual network adapters provide advanced configurations options, such as MAC address spoofing and Dynamic Host Configuration Protocol (DHCP) guard, which can enhance network security in virtualized environments.

Virtualized network security refers to the methods and technologies used to protect virtualized networks and their components, such as virtual machines, virtual servers, and other virtual network devices, from cyber threats and vulnerabilities. Implementing security measures for virtualized networks is essential to ensure the confidentiality, integrity, and availability of resources and data. In a virtualized environment, security policies and procedures must account for data isolation, access control, hypervisor security, and network segmentation. Virtual security appliances, such as virtual firewalls, intrusion detection systems, and intrusion prevention systems, can be deployed to enhance the security posture of virtualized networks and offer advanced threat protection capabilities.

Cloud networking is a concept in network virtualization that leverages cloud computing resources to deliver network services and infrastructure. This approach centralizes management, reduces hardware dependency, and provides scalability and flexibility to users. Cloud networking includes various technologies such as Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS), which enable users to access computing resources on demand without the need for maintaining physical hardware. Cloud networking also promotes the use of software-defined networking (SDN) and network functions virtualization (NFV) to enable better network management and automation across various cloud-based services and applications.