VPN passthrough: What is it and how does it work?

VPN passthrough

What is a VPN Passthrough?

A VPN (Virtual Private Network) passthrough is a function on a network router that allows devices on a private network to establish outbound VPN connections while maintaining the security features of the router. It's particularly significant because most home routers use Network Address Translation (NAT), which can interfere with VPN traffic.

How Does a VPN Passthrough Work?

The workings of a VPN passthrough involve several technical aspects of both NAT and VPN protocols. It allows VPN packets to traverse through NAT devices by modifying how the router handles this traffic.

Types of VPN Passthrough

  • IPsec Passthrough: This allows the IPsec protocol, used by many corporate VPNs, to pass through the router.
  • PPTP Passthrough: Permits PPTP VPN traffic. PPTP is an older VPN protocol, less secure than others.
  • L2TP Passthrough: Allows L2TP VPN, a more secure protocol than PPTP, to pass through the router.

Detailed Mechanism:

  • Handling VPN Protocols: Each VPN protocol - IPsec, PPTP, and L2TP - has unique requirements for data packets. A VPN passthrough is configured to recognize and properly route these packets.
  • IPsec Passthrough: IPsec NAT Traversal (NAT-T) is used for IPsec passthrough. It encapsulates IPsec packets in UDP packets, which can more easily pass through NAT.
  • PPTP and L2TP Passthrough: These involve allowing GRE (Generic Routing Encapsulation) and other necessary protocols through the NAT. GRE is used by PPTP and is necessary for the router to correctly forward PPTP traffic.
  • Dynamic Port Management: VPN passthrough dynamically manages port settings and IP addresses for the VPN traffic, ensuring that the packets reach their intended destination without getting blocked by the router’s NAT or firewall.
  • Security Implications: While VPN passthrough facilitates VPN connections, it doesn't compromise the router's security. It carefully manages which ports are opened and when, based on active VPN connections.

In essence, a VPN passthrough modifies the standard behavior of a router's NAT to allow for the specific requirements of VPN protocols. This ensures that users can establish secure VPN connections from within a NAT-enabled network without compromising the security that NAT provides.

How to Enable VPN Passthrough

Enabling VPN passthrough varies by router, but generally involves accessing the router's settings via a web browser, navigating to the security or VPN settings, and enabling the passthrough for the required VPN protocols.

  • Access Router Settings: Usually done by typing the router's IP address into a web browser.
  • Locate VPN Settings: Often under “Security” or “Advanced Settings”.
  • Enable Passthrough Options: Enable the types of VPN passthrough needed (IPsec, PPTP, L2TP).

Do I Need a VPN Passthrough?

Whether you need a VPN passthrough depends on your use of VPNs at home. If you or someone in your household needs to connect to a workplace VPN or a secure internet service via a personal VPN service, you will likely need this feature enabled. However, for newer VPN protocols like OpenVPN or those using SSL, a passthrough might not be necessary.

In summary, a VPN passthrough is a router feature that allows VPN traffic to pass through it, crucial for older VPN protocols working with NAT and firewalls. The need for a VPN passthrough depends on your VPN usage and the type of VPN protocol you're using.