How VPNs Work: Tunneling, Encryption, and When to Use One

What Is a VPN?

A Virtual Private Network (VPN) is a technology that creates a secure, encrypted connection—a "tunnel"—between your device and a VPN server, routing your internet traffic through that server before it reaches its destination. From the perspective of websites, services, and anyone monitoring your network connection, your traffic appears to originate from the VPN server's IP address and location rather than your actual IP address. The encryption prevents anyone who intercepts the traffic in transit from reading its contents.

VPNs were originally developed in the late 1990s to allow remote employees to securely access corporate networks over the public internet—essentially extending the corporate network to wherever the employee happened to be. This use case remains important: enterprise VPNs allow employees to reach internal resources as if they were physically in the office. Consumer VPNs, which emerged as a separate market, focus on privacy and bypassing geographic content restrictions, and have become a mass-market product with hundreds of competing providers.

The VPN market has exploded in the past decade as privacy awareness has grown. Millions of people use consumer VPNs to prevent their internet service provider (ISP) from seeing their browsing history, to access streaming content unavailable in their country, to secure their traffic on public Wi-Fi, or to avoid surveillance in countries with restrictive internet policies. However, VPNs are frequently misunderstood tools—they provide specific protections but are not a complete privacy or anonymity solution.

How VPN Tunneling Works

When you connect to a VPN, your device establishes an encrypted tunnel to the VPN server. All your internet traffic is wrapped in an additional layer of encryption and sent through this tunnel. The process involves encapsulation: your original data packets are encrypted and then wrapped inside new packets that are addressed to the VPN server. This encapsulation is what gives VPNs their tunnel-like nature—the original packet travels inside a secure outer packet.

At the VPN server, the outer packet is removed, the inner packet is decrypted, and the original traffic is forwarded to its intended destination—a website, streaming service, or any other internet resource. The response travels back to the VPN server, which encrypts it and sends it back through the tunnel to your device. From your device's perspective, it looks like you are connected directly to the internet via the VPN server. This entire process introduces a small amount of latency because your traffic takes a longer path and requires encryption and decryption at both ends.

The VPN client software on your device handles the key exchange, authentication, and encryption. When you first connect, the client and server perform a handshake—a mutual authentication process using certificates or pre-shared keys—and negotiate the encryption algorithms and session keys to be used. These session keys are ephemeral, meaning they are discarded after the session ends and new ones are generated for each connection. This property, called Perfect Forward Secrecy (PFS), ensures that if an attacker records encrypted traffic and later obtains the long-term private key, they still cannot decrypt past sessions.

VPN Protocols

OpenVPN is one of the most widely used and trusted VPN protocols. It is open-source, extensively audited, and highly configurable. OpenVPN uses the OpenSSL library for its cryptographic operations and can run over both UDP (faster) and TCP (more reliable through firewalls). Its transparency and flexibility make it the protocol of choice for many security-conscious users and organizations, though its complexity makes it somewhat slower to connect than newer protocols.

WireGuard is a newer protocol that has gained rapid adoption since its inclusion in the Linux kernel in 2020. It has a dramatically smaller codebase than OpenVPN (roughly 4,000 lines versus hundreds of thousands), making it faster to audit and less likely to contain security vulnerabilities. WireGuard is also significantly faster than OpenVPN in terms of throughput and connection time, and handles network changes (such as moving from Wi-Fi to cellular) more gracefully. Most major VPN providers now support WireGuard.

IKEv2/IPsec (Internet Key Exchange version 2 with IPsec) is particularly popular on mobile devices because it reconnects quickly when the network changes and is natively supported by iOS and Android. It is fast, secure when properly configured, and well-suited to mobile use cases. L2TP/IPsec and PPTP are older protocols that are largely deprecated—PPTP in particular has known security weaknesses and should not be used. SSTP (Secure Socket Tunneling Protocol) is a Microsoft-developed protocol that is tightly integrated with Windows and useful in environments where other VPN traffic is blocked, since it uses port 443 like HTTPS.

What VPNs Protect You From

A VPN prevents your ISP from seeing the content of your traffic and from knowing which specific websites and services you visit. Without a VPN, your ISP can see every DNS query you make and every IP address you connect to. In many countries, ISPs are legally required to retain this browsing history data and may sell it to advertisers or hand it to government agencies on request. A VPN moves that visibility from your ISP to the VPN provider, which is why choosing a trustworthy provider with a verified no-logs policy matters enormously.

On public Wi-Fi networks—coffee shops, airports, hotels—unencrypted traffic is vulnerable to interception by anyone else on the same network. A VPN encrypts all your traffic before it leaves your device, preventing attackers from reading it even if they intercept it. However, it is worth noting that HTTPS already encrypts the content of most web traffic; what a VPN adds on public Wi-Fi is protection of metadata—which sites you visit—and protection against SSL stripping attacks that attempt to downgrade HTTPS connections to HTTP.

VPNs allow you to appear to be in a different geographic location by connecting to a server in another country. This lets you access streaming content libraries (Netflix UK, for example, has different content than Netflix US), bypass censorship in countries that block certain websites, and avoid price discrimination based on location. Journalists, activists, and whistleblowers in countries with restrictive internet policies often rely on VPNs to access blocked information and communicate securely.

What VPNs Do Not Protect You From

A VPN does not make you anonymous. Websites can still track you through cookies, browser fingerprinting, and login accounts. Advertising networks build profiles based on behavior, not just IP addresses. If you log into Google or Facebook while using a VPN, those companies still know who you are and can correlate your activities. A VPN also does not protect against malware on your device—if your computer is infected, a VPN does not prevent the malware from doing its work or exfiltrating your data.

A VPN protects traffic between your device and the VPN server, but traffic from the VPN server to the destination website is unencrypted (unless the destination uses HTTPS). The VPN server itself sees all your traffic. This is why provider trustworthiness is critical: a malicious or careless VPN provider is worse than no VPN at all. Many free VPN providers monetize by logging and selling user data, injecting ads, or have extremely poor security practices. Audited, no-logs VPN providers with a clear business model (subscription fees) are generally far more trustworthy.

VPNs also do not protect against DNS leaks (where DNS queries bypass the VPN tunnel and are visible to your ISP) or WebRTC leaks (where browser technology can expose your real IP address). Quality VPN clients prevent these leaks, but users should verify with leak-testing tools. A kill switch—a feature that blocks all internet traffic if the VPN connection drops—prevents your real IP from being exposed during brief disconnections. For users who require strong anonymity rather than mere privacy, Tor (The Onion Router) provides much stronger anonymity guarantees than any VPN, though at the cost of significantly slower speeds and some usability limitations.

Choosing a VPN and Use Cases

When choosing a consumer VPN, the most important factors are the provider's privacy policy and whether it has been independently audited and verified. Providers like Mullvad, ProtonVPN, and ExpressVPN have undergone third-party audits of their no-logs claims and infrastructure. Jurisdiction matters too—a provider based in a country that is part of intelligence-sharing alliances (the Five Eyes, Nine Eyes, or Fourteen Eyes) may be subject to legal orders to hand over data or secretly install wiretaps. A provider that genuinely stores no logs has nothing to hand over even under legal compulsion.

Performance should be considered based on your use case. If you primarily need a VPN for streaming, you want a provider with fast servers in many countries. If privacy is the priority, you may prefer a provider like Mullvad that accepts anonymous payment (cash, cryptocurrency) and does not require an email address to sign up. For corporate use, a dedicated enterprise VPN or Zero Trust Network Access (ZTNA) solution is typically more appropriate than a consumer service.

The right time to use a VPN includes: connecting to public Wi-Fi, accessing sensitive accounts or conducting financial transactions outside your home network, traveling to countries with censored internet, downloading files (a VPN can separate your IP from your downloads), or when privacy from your ISP is a priority. A VPN is not necessary for every internet activity and adds latency, so many users run VPNs selectively or use split tunneling—a feature that routes only specific traffic through the VPN while letting other traffic reach the internet directly. Understanding what a VPN actually does—and does not do—helps you use it as an effective component of a broader privacy and security strategy.