VPN passthrough is a router feature that lets VPN traffic pass through the router’s firewall so a device on your network can successfully connect to a remote VPN server. In practice, it makes sure older VPN protocols are recognized and not blocked or dropped by the router’s NAT and firewall.

Quick Scoop

  • VPN passthrough allows VPN connections (like IPSec, L2TP, PPTP) to traverse a router’s firewall and NAT so the VPN can connect properly.
  • It exists mainly for older VPN protocols that don’t naturally play well with modern home/office routers using NAT.
  • Many modern VPN protocols (such as OpenVPN or WireGuard) don’t need passthrough at all because they’re designed to work with NAT by default.

What is VPN passthrough?

VPN passthrough is a setting on many home and small-business routers that tells the router to recognize and correctly forward VPN packets instead of treating them as suspicious traffic. Without it, some VPN connections may fail to establish, hang during connection, or disconnect quickly because the router drops or mishandles the encrypted packets.

In simple terms, it “opens a special lane” through the firewall for specific VPN protocols so they can create and maintain a secure tunnel to a VPN server on the internet.

How does it work (simple version)?

  • The router inspects traffic going out from your device and sees packets that match certain VPN protocols (PPTP, L2TP, IPSec).
  • Instead of blocking or losing track of these packets due to NAT, the router applies special rules to keep the VPN session state and forward them to the correct destination.
  • For protocols like IPSec/L2TP, this often involves allowing specific UDP ports (for example 500 and 4500) and handling NAT traversal so the encrypted traffic can flow correctly.

Modern routers often have VPN passthrough enabled by default, and the option typically appears under security or advanced settings for PPTP, L2TP, and IPSec.

When do you need it?

You usually need VPN passthrough if:

  • Your VPN client uses older protocols like PPTP, L2TP, or classic IPSec.
  • Your router has a strict firewall/NAT that otherwise blocks or breaks these connections.
  • You are connecting from behind a home or office router that is not itself acting as the VPN endpoint, but just forwarding traffic.

You typically do not need VPN passthrough if your VPN uses NAT-friendly protocols (for example OpenVPN over UDP/TCP or WireGuard), or if your router is directly running the VPN client/server instead of simply passing traffic.

Pros and cons

Benefits

  • Lets legacy VPN protocols work behind modern NAT routers.
  • Allows remote workers or home users to reach corporate VPNs that still rely on PPTP/L2TP/IPSec.
  • Preserves firewall protection for other types of traffic while only “special-handling” VPN packets.

Drawbacks

  • Focused on older protocols that may be less secure or increasingly deprecated.
  • Misconfiguration can create holes or unexpected behavior in your firewall if settings are changed without understanding them.
  • Often unnecessary today if both router and VPN support modern, NAT-ready protocols, in which case using those is usually the cleaner solution.

Mini FAQ

Is VPN passthrough the same as having a VPN router?
No. A VPN router runs the VPN client/server itself, while VPN passthrough simply forwards VPN traffic from devices behind it.

Should you turn it on?
If you are using an older VPN protocol and connections keep failing or dropping, enabling the matching passthrough option for that protocol can help. If everything already works using a modern protocol, you usually don’t need to change this setting.

Information gathered from public forums or data available on the internet and portrayed here.