**1. Introduction**

The concept of virtual has different connotations, depending on the domain in which it is used: philosophy [1], current speech [2], creation of artificial ambients of virtual reality type [3], etc. Most of the time, the term usually refers to applications and services from the Internet. *The virtual experiment* represents an alternative, or better said a complementary, resource in the study of phenomena and processes.

The basis of the concept of *hardware virtualization* (also known as platform virtualization) consists in the use of software in order to simulate the existence of a hardware component. This allows the use of multiple independent Information and Communications Technology (ICT) systems within a single physical computational system. The term 'virtualization', in this sense, was used even in the 1960's mainframes, and it represented as a method of partitioning the resources of a mainframe to all its diverse applications [4].

A *virtual machine* (VM) is a software application that completely simulates all the functions of all hardware components of an informatics system (particularly, a computer). If on a real hardware system (further named as host) are installed multiple virtual machines, each one of them will function as an independent computational system, complete with its own processor,

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its own RAM memory, its own Hard Disk Drive (HDD), etc. The operating system that allows the creation and continued simulation of more virtual machines is called a *Hypervisor* or a virtual machine manager.

At first, hypervisors can be classified into two distinct types: hypervisors of type 1 and hypervisors of type 2. Those of type 1 represent a hypervisor that runs directly on the host. Those of type 2 run within an operating system, which in turn runs on the host [5]. Hypervisors of type 1 are therefore more efficient, but because of this, their monetary cost increases considerably. Thus, in order to experience virtualization, it is often preferred to use a type 2 hypervisor, before entering in the possession of a type 1 hypervisor.

VMware vSphere (known also under the name of ESXi) [6] represents a type 1 hypervisor for servers. ESXi runs directly on the server (the host) and allows the creation and utilization of multiple virtual servers. VMware Workstation [7] is a type 2 hypervisor; it allows the user to create and run in parallel, multiple instances of virtual machines with operating systems compatible to x86 or x86-64 architectures on the same physical host.

Depending on the level of virtualization, hypervisors can be classified [7] as having:


Desktop (work area) virtualization represents the concept of separation between the logical desktop and the physical machine. A form of desktop virtualization is represented by virtual desktop interface (VDI) that represents a more advanced form of hardware virtualization. Instead of having to interact with a host directly with a mouse, a keyboard and/or a monitor, the user can interact with the host via another machine—another desktop computer, or a smartphone, etc. This can be accomplished through a LAN network connection or a wireless LAN network connection or even the Internet. In this situation, the host becomes a server computer capable of running several virtual machines at the same time for multiple users. As a first example, the TeamViewer application, developed by TeamViewer GmbH [8], allows remote access and control of a desktop and file transfer between the two devices (a host PC (personal computer) and another device such as a PC or a smartphone). As a second example, more advanced than a connection to a single desktop (TeamViewer's situation), HP and IBM companies offer a VDI hybrid, with a series of virtualization software, in order to improve the computational limitations of a client [9].

Session virtualization allows multiple users to connect and authenticate simultaneously to a more powerful computer via a network. Each user has a personal desktop and a personal folder in which he can store his data [10]. With the multi-seat configuration, session virtualization can be achieved by connecting more input/output devices to a single personal computer.

Another form of virtualization consists in the movement of all the desktops to a cloud, thus creating hosted virtual desktops (HVDs) in which the desktops are stored and maintained by a hosting specialized business. Here, the benefits include a drastic decrease of the investment funds (in informatics equipment), which is replaced by a monthly 'rent' towards the hosting business [11].

In the second section of this paper, the application HypeRSimRIP ('hypervisor de Rețele cu simulator RIP' [Ro]—network hypervisor with integrated RIP simulator [Eng.]) is presented. This application is a type 2 hypervisor with full virtualization, which was developed by the authors in order to allow the construction, management and observation of a virtual system of Internet Protocol (IP) networks. The HypeRSimRIP application is useful in realizing virtual experiments dedicated to the study of IP networks. Moreover, the subject is of huge interest, considering that the world has embraced the Internet of Everything (IoE) concept—the connection of the Internet to all humans, processes, data and objects. The theoretical aspects, specific to IP networks, like the Open Systems Interconnection model (OSI) and TCP/IP models, the TCP/IP protocol suite, IPv4 addressing (sub-netting and variable length sub-net mask (VLSM) methods), the routing process, the RIPv1, RIPv2 and RIPng protocols are considered known, and they will not be presented in this paper. For further references, please consider [12–17].

In the third and final section of this paper, the functionality of the HypeRSimRIP application is described, alongside with some utilization examples. The application allows the simulation of notable experiments from the IP network domain. The results obtained by HypeRSimRIP are similar to the theoretical results obtained in the literature.
