Two benefits of tunneling are encrypted connections and access to resources behind the firewall. When it comes to interoperability, however, establishing these connections is sometimes difficult for Linux clients. Linux distributions often have issues with establishing virtual private network (VPN) connections with servers based in other environments, mainly because the GUI applications used to establish those connections have trouble staying in sync with the pace of Linux development. It is often two steps forward, and once step back: When each distribution ships, the shared libraries often get changed, and your favorite VPN application that used to work no longer succeeds with cross-platform connections. Recently the situation has improved. In this article, I look at some tips for establishing VPN connections from the Linux desktop.

A VPN creates a point-to-point tunnel over a public network. A number of protocols support VPN connections, including the following popular options:

• L2TP over IPsec – Cisco's primary tunneling protocol. L2TPv3 is the latest version, but make sure you choose a version appropriate for your network. Remember that two major implementations of IPsec are available in Linux systems. For example, older systems use FreeS/WAN or Openswan for IPsec. Newer systems with any version of the standard 2.6 kernel have native IPsec support.
• Point-to-Point Tunneling Protocol (PPTP) – An older protocol that still is used in many Microsoft environments.
• Secure Sockets Layer/Transport Layer Security (SSL/TLS) – One of the most powerful interoperability protocols available SSL/TLS supports many types of VPN connections. OpenVPN [1], for example, is an SSL/TLS-based tunneling solution.

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