VPN is more relevant now than ever before. Even home routers are starting to feature not just VPN servers, but ones with hardware-accelerated encryption. So what exactly is VPN and what's it for? Let's try to explain it in simple terms.

What is VPN?

Somehow, even textbooks don't provide an extended and in-depth definition of what VPN is. They say it's obvious anyway: the abbreviation VPN stands for Virtual Private Network, that is, a virtual private network. And why discuss anything else? What a «network» is — is clear: at a primitive level, it's the combination of two or more nodes by some type of connection so that they can exchange information. Naturally, in the most convenient way and with support for all necessary services.

What «private» means also seems obvious — not public, therefore private. That is, one where not just anyone is present, but only authorized nodes. If you dig a little deeper, this component of VPN is actually the most important, as it determines a number of requirements for this very «privacy».

First, you need to somehow mark the participants of this network and the information they exchange so that it doesn't get mixed with someone else's. Second, it's definitely useful to protect this information from prying eyes. At least encrypt it, which again imposes the next round of limitations related to the strength of this encryption.

Third, you need to maintain the integrity of this method of information transmission — not let outsiders into the private network, verify the source of transmitted messages, and ensure that information doesn't leak anywhere in «plain text». In general, it's like at private parties of the powerful: they make noise all around, but who and what is doing what there — is unclear. And strict security at the entrance and exit conducts not only face control, but control of other places as well.

With the concept of «virtual» everything is a bit simpler. It just means that such a network is abstracted from the physical component — it doesn't matter through which and how many communication channels it is laid, as for the participants of this network it works transparently. Or, on the other hand, the physical network most often simply doesn't belong to the user of the virtual one.

For example, in serious organizations, employees are required to immediately use a VPN connection to the office network when connecting a work laptop to any wired or wireless networks located outside the walls of that very organization. It doesn't matter through what exactly this connection will be established, but you can be sure that it will go through public, someone else's communication networks. Such a connection is called a tunnel, and we'll encounter this term more than once later.

What is VPN needed for?

The above example of connecting a remote user to a corporate network is one of the most typical VPN usage scenarios. The user feels like they're at home — rather, at home, on vacation, or on a business trip they can feel like they're at work and can use corporate services without problems.

At the same time, an attacker won't be able to just snoop what exactly this user is doing, what data they are transmitting and receiving. Moreover, in companies concerned about their own security, mandatory use of VPN connections is forcibly enabled on all devices used by workers, wherever they are. Even Internet use in this case goes through the corporate network and under the strict supervision of the security service!

The second most common usage option is similar to the first, only not individual users connect to the corporate network, but entire offices or buildings. The goal is the same — to reliably and securely combine geographically remote elements of one organization into a single network.

These can be both large corporate offices in different countries, and meat stalls of LLC «Horns and Hooves» scattered around the city. Or even just cameras, alarms, and other security systems. With such simplicity of creating VPN — after all, you don't need to lay cable each time — virtual private networks can be created within companies to combine and isolate certain departments or systems.

VPN networks are also frequently organized between servers or entire computing clusters to maintain their availability and data duplication. The frequency of their use is directly related to the growth in popularity of cloud technologies. Moreover, all of the above — these are not some temporary solutions: such connections can be (and are) maintained for years.

However, now there is a transition to the next level of abstraction — SDN (Software Defined Networks), which will bring quite a few surprises, both pleasant and not so much. However, this is a separate and very extensive topic that we won't touch on now.

Russia has its own, special path of practical VPN application. Once large ISPs built their networks based on simple unmanaged switches — obviously, to save money. To separate client traffic, they began to use various variants of VPN connections to the provider's server, through which they provided Internet access.

Surprisingly, but this method is still used today, and manufacturers of home routers for the Russian region are still forced to add support for such connections to the firmware of their devices. So in some sense, Russia was a leader in the number of simultaneous VPN connections among Internet users.

A counterexample of such permanent VPN connections is session-based connections. They are often used when providing client access to various services, which, as a rule, are related to processing very sensitive information in the fields of finance, healthcare, and jurisprudence.

However, for the ordinary user, another option of practical VPN use is much more important. In our security tips for Android and iOS we strongly recommend using a secure VPN connection to a reliable node (be it a home router or a special VPN provider) when connecting to any public networks, to protect your traffic from possible interference by attackers!

Finally, the last option for using VPN privately — is to bypass various network restrictions. For example, to gain access to resources that are blocked or don't provide their services in a certain territory. According to a GlobalWebIndex report, in 2014 alone, about 166 million people used VPN to access social networks.

Conclusion

In general, it's obvious that VPN nowadays is a useful, necessary thing that is constantly gaining popularity. Of course, we told about this technology and its capabilities in the most general terms — in real life there are many nuances related to its use, including legislative ones, not just technical ones. And certainly our story will be incomplete without describing popular VPN implementations and their development. We'll talk about this in the next two parts of our series.