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If you've bitten the bullet on any of the major VPN services, you likely have access to some pretty robust protocols. Generally speaking, most of these will work out of the box, without any fiddling around with router or internet settings. But what if you're using a VPN that relies on a legacy protocol and are experiencing issues with your connection? In that case, a VPN passthrough is probably something you should be on a first-name basis with. The aptly named router setting allows certain VPN protocols to pass through the firewall. In layman's terms, it works a bit like an employee ID card by helping the router recognize specific data packets associated with the service you're using.

No shame if you've never heard of this feature's existence, though. Unless you're running a custom setup or sticking with an older protocol, most routers these days automatically recognize VPN traffic. However, you may want to confirm whether this feature is manually enabled through the router's admin panel, as it can present a small security risk if left unchecked.

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A VPN passthrough is a remnant of the old days when VPNs relied on different protocols. It all boils down to something commonly referred to as the NAT, or network address translation. The router's NAT reads information about incoming and outgoing connections to determine which traffic gets the green light and which is a no-no. Since VPN passthrough helps the router identify the "masked" connection, it allows VPN clients to connect to a server outside the base network unimpeded.

If you fire up a VPN to stream geo-blocked content (one clever way to use the service), the connection is likely facilitated by the WireGuard protocol, which already works with most modern routers. A VPN passthrough isn't really needed since the router simply receives all the NAT information it requires from the protocol by default. Yet routers can struggle to recognize older protocols like PPTP, which is the key reason why the VPN passthrough remains a thing.

While a premium VPN is worth it because it makes these settings a non-issue, there are a few reasons to look for the passthrough configurations. Some people are still using older VPN setups, in which case, looking at these options is a good first troubleshooting step. Or, you may want to shut it down for security reasons. Either way, the process is relatively straightforward.

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In case you're unsure if you've got this feature, start by doing a quick Google search for your particular model. All clear? Then go ahead and access your router's admin panel. Fire up any internet browser, copy the router's IP from the device's network settings, and paste it into the address bar. After entering your router credentials, look for the Advanced Settings (the name may vary between router models). There, you'll be able to find VPN passthrough preferences for a variety of legacy protocols.

Depending on your POV, knowing what a VPN passthrough is may seem like a useless bit of knowledge. It's overkill for most modern VPNs, after all, so why even care? Though the security repercussions may be negligible for most users, this feature does leave a few small gaps in your network wide open. For instance, the archaic PPTP protocol has its fair share of vulnerabilities, including a flawed authentication system and poor encryption. Leaving the passthrough open and "collecting dust" may expand your attack surface, so if you don't need this feature (like when you're already using WireGuard or OpenVPN), it's really just best to shut it down altogether.