VPN Passthrough: What Is It & How It Works

You may have come across the term VPN passthrough while checking your router settings. The name sounds technical, but it refers to a router feature that lets VPN traffic pass through Network Address Translation (NAT) without getting blocked. 

Whether you need to enable VPN passthrough depends mainly on the VPN protocol and the router. In many cases, it is already handled automatically. In this guide, we will break down how the feature works, when it is needed, and how to enable it.

Key Takeaways

• VPN passthrough helps PPTP, L2TP, and IPsec connections move through a router when NAT cannot handle the traffic correctly.

• Most users do not need to enable it manually because many routers support passthrough by default.

• Modern protocols like WireGuard and OpenVPN work through NAT without a dedicated passthrough setting.

• Each passthrough option should match the protocol in use, so there is no reason to enable all of them.

What Is VPN Passthrough?

VPN passthrough is a router feature that allows a device on your network to connect to a VPN server when Network Address Translation interferes with the VPN protocol. It is mainly associated with PPTP, L2TP, and IPsec connections, which some routers need extra support to process correctly.

The name comes from what the feature does: it lets VPN traffic pass through the router instead of being blocked or mishandled. It does not create the VPN connection itself and simply helps the router recognize and forward traffic from protocols that may otherwise run into problems.

How Does VPN Passthrough Work?

When you connect to a VPN, the traffic travels from your device through the router before reaching the VPN server. The router uses NAT to manage that connection and send returning traffic back to the right device. However, some VPN protocols like PPTP, L2TP, and IPsec do not always work cleanly with NAT. 

As a result, the router may block the traffic or fail to send it where it needs to go. This is where VPN passthrough comes into play. It helps the router process that traffic and let it continue to the VPN server. The way it does this depends on the passthrough type involved, which we will cover next. 

Types of VPN Passthrough

Routers that support VPN passthrough usually provide separate settings for PPTP, L2TP, and IPsec. Each one handles a different type of VPN traffic and works slightly differently with NAT:

PPTP Passthrough

PPTP uses a TCP connection to establish the tunnel and GRE to carry the VPN traffic. Since GRE does not use TCP or UDP ports in the usual way, NAT may struggle to track the connection and return traffic to the correct device. PPTP passthrough gives the router the extra handling needed to keep the connection working.

L2TP Passthrough

L2TP carries tunnelled traffic over UDP port 1701. It does not provide encryption on its own, so VPN connections commonly pair it with IPsec for authentication and data protection. L2TP passthrough allows this traffic to move through the router when NAT would otherwise interfere with the connection.

IPsec Passthrough

IPsec passthrough helps IPsec traffic travel through a router using NAT. Modern IPsec connections can use NAT Traversal, or NAT-T, which places ESP traffic inside UDP packets so the router can process it more easily. Some routers still provide a separate IPsec passthrough setting for connections that require it.

Note: If WireGuard or OpenVPN is available in your VPN app, there is little reason to rely on an older passthrough option. Both can get through NAT on their own and offer stronger, more modern protection.

• Read: TCP vs UDP: What is the Difference Between Both Protocols?

How to Enable VPN Passthrough on a Router

The location of the VPN passthrough setting depends on the router. Some models enable it automatically, while others let you control PPTP, L2TP, and IPsec passthrough separately. To enable it manually:

1. Connect your device to the router through WiFi or an Ethernet cable.
2. Open the router’s administration page in a web browser.
3. Sign in using the router administrator credentials.
4. Look for VPN Passthrough or NAT Passthrough. The setting may appear under VPN, WAN, Security, Firewall, or Advanced settings.
5. Enable the option that matches the VPN protocol you are using.
6. Save or apply the changes.
7. Restart the router if prompted, then reconnect to the VPN.

If you cannot find a passthrough setting, check the support page or manual for your router model. The feature may already be active without a separate switch.

Do I Need VPN Passthrough?

Probably not. Most users will never need to enable VPN passthrough manually. Here is why:

• Your router may already handle it: Many routers include passthrough support for PPTP, L2TP, and IPsec, and some manufacturers enable it by default. If your VPN connects without any trouble, there is nothing to change.

• It only matters when using older protocols: PPTP, L2TP, and IPsec can run into problems with NAT because the router may not process their traffic correctly. VPN passthrough gives the router the extra support needed to let those connections through.

• High-quality VPNs support modern protocols: PureVPN offers WireGuard, OpenVPN, and IKEv2 to choose from, so you are unlikely to need one of the older passthrough options during normal use.

Security Considerations When Using VPN Passthrough

VPN passthrough only helps a connection get through NAT. It does not strengthen the encryption or fix security weaknesses in the protocol being used. For example, PPTP remains outdated even when PPTP passthrough is enabled, whereas L2TP does not encrypt traffic unless it is paired with IPsec.

Enable only the setting that matches the connection you need. There is no reason to turn on PPTP, L2TP, and IPsec passthrough together if only one protocol is in use. Keep the router firmware updated as well because updates can fix connection issues and patch known security vulnerabilities.

Frequently Asked Questions