Server switching is a feature -- offered by most VPN service providers -- that allows you to change what region or country you're going to connect to. Most providers allow you to switch as often as you'd like (although you usually have to disconnect, then change your configuration, and reconnect). This may be useful if you're trying to hide your location, or if you're running into some communications glitches on the server you're currently using.

A firewall uses packet filtering to allow or disallow the flow of specific types of network traffic. IP packet filtering provides a way for administrators to define precisely what IP traffic is allowed to cross the firewall. IP packet filtering is important when private intranets are connected to public networks, such as the Internet. There are two approaches to using a firewall with a VPN server:

Mobile VPNs are designed and optimized to ensure a seamless user experience when devices are switching networks or moving out of coverage. It generally has a smaller memory footprint, and because of that, it also requires less processing power than a traditional VPN. Therefore, it enables your applications to run faster while the battery pack is able to last longer.
A VPN client on a remote user's computer or mobile device connects to a VPN gateway on the organization's network. The gateway typically requires the device to authenticate its identity. Then, it creates a network link back to the device that allows it to reach internal network resources -- e.g., file servers, printers and intranets -- as though the gateway is on the network locally.
With  multiple clients, rich with different features, it’s no wonder this VPN service handles more than 10 million users. It covers Microsoft’s and Apple’s operating systems, but also iOS and Android. The interface is not the best out there and could definitely use some work, but these disadvantages are easily overshadowed by the awesome features this VPN offers.
Security is second to none with NordVPN. Its kills switch feature always monitors traffic between devices and the VPN servers. If for some reason, the data stream breaks, the kill switch will automatically terminate the connection, ensuring that your traffic is protected from prying eyes. Also, a DNS leak feature changes your DNS to point to the VPN server, ensuring that hackers cannot steal data from your default DNS.

We spent more than 130 hours over four months researching 32 VPN services, testing 12, interviewing the leadership of five, and consulting information security and legal experts about our results. We found that most people should prioritize other security tools and privacy practices first, but in the cases where a VPN makes sense—such as when you're connecting to public Wi-Fi—IVPN is the most trustworthy provider that offers fast, secure connections with an easy setup process on both computers and mobile devices.

It usually relies on either Internet Protocol Security (IPsec) or Secure Sockets Layer (SSL) to secure the connection. However, SSL VPNs can also be used to supply secure access to a single application, rather than an entire internal network. Some VPNs also provide Layer 2 access to the target network; these will require a tunneling protocol like PPTP (Point-to-Point Tunneling Protocol) or L2TP (Layer 2 Tunneling Protocol) running across the base IPsec connection.
Many VPN services also provide their own DNS resolution system. Think of DNS as a phone book that turns a text-based URL like "" into a numeric IP address that computers can understand. Savvy snoops can monitor DNS requests and track your movements online. Greedy attackers can also use DNS poisoning to direct you to bogus phishing pages designed to steal your data. When you use a VPN's DNS system, it's another layer of protection.