What Is VPN Passthrough? (And Why You Probably Don’t Need It)

If you're using a modern VPN app like Windscribe, you likely don't need to worry about VPN passthrough at all.

Modern protocols, specifically WireGuard, OpenVPN, and IKEv2, are designed to handle Network Address Translation (NAT) natively, effectively making manual passthrough settings a relic of the past.

Despite being largely obsolete for the average user, the feature still matters because it remains a common fixture in router settings and corporate network configurations.

It was originally designed to help older, less flexible protocols like PPTP and L2TP pass through (get it?) a router’s firewall, and it continues to appear in troubleshooting guides today. 

Still, understanding this feature can help if you’re troubleshooting weird connection issues at the office or dealing with outdated hardware.

In this guide, we’ll explain what it does and why you probably won’t need to touch it. 

What Is VPN Passthrough?

Simply put, it’s a router feature that allows VPN traffic using older protocols, like PPTP, L2TP, and IPsec, to pass through the router’s NAT (Network Address Translation) firewall without being blocked.

Okay, in human terms, this means your router steps aside and lets that older kind of VPN connection get through instead of accidentally stopping it.

It’s kind of like a security guard recognizing an awkward old delivery truck and lifting the gate so it can enter. Without that, the truck just sits outside looking confused. 

So why does VPN passthrough even exist if newer VPN protocols don’t need it? Because older VPN protocols don’t play nice with the way routers handle traffic.

Routers like clear labels so they know where to send things. Older VPN protocols can hide or scramble some of that information, which makes the router more likely to get confused and block the connection by mistake.

VPN passthrough basically tells the router, “Yes, this weird-looking traffic is fine. Let it through.”

Another easy way to think about it: NAT is like a hotel front desk sorting packages by room number. Older VPN protocols sometimes show up with the room number missing or hard to read. Passthrough tells the front desk not to panic and to forward the package anyway.

But VPN passthrough doesn’t create the VPN connection. It doesn’t encrypt anything. It simply removes the router-level roadblock so the actual VPN app or VPN client on your device can connect to the VPN server.

How Does VPN Passthrough Work?

Most home routers use something called NAT, which stands for Network Address Translation. Its job is simple: it lets multiple devices in your home share one public IP address. So your phone, laptop, TV, and game console can all get online through the same router without each needing their own public IP.

To keep all that traffic organized, NAT tracks outgoing connections using things like IP addresses and port numbers.

A port number is basically a little label that helps the router tell one connection apart from another, so when data comes back, it knows which device to send it to.

The problem is that some older VPN protocols don’t work well with that system. For example, PPTP uses something called GRE (Generic Routing Encapsulation), which doesn’t use normal port numbers the way most internet traffic does, and IPsec encrypts parts of the packet headers, which are the bits of information the router normally reads to figure out where traffic should go. So the router sees this strange-looking traffic, cannot properly label it, and may just block or drop it.

When VPN passthrough is enabled, the router uses protocol-specific tricks to help these older VPNs get through.

With PPTP, it can use a Call ID as a stand-in for a port number. With IPsec, it can use NAT-T (aka, NAT Traversal), which wraps the VPN traffic inside UDP packets that NAT can understand. This wrapping process is called encapsulation.

So VPN passthrough is really just your router doing a bit of translation work, so older VPN traffic doesn’t get rejected. 

Types of VPN Passthrough

Each type of passthrough is designed to help a specific protocol get through NAT without being blocked. And while most of these protocols are now badly outdated, they’re still relevant in certain business or legacy setups. 

PPTP Passthrough

At this point, PPTP is basically a dinosaur fossil. It uses TCP port 1723 for setup, but the actual data tunnel runs through GRE, which doesn’t use normal port numbers.

That’s a problem because NAT loves port numbers. They’re how it keeps track of who sent what and where replies should go.

Without them, the router starts squinting at the traffic like it’s reading a smudged shipping label. PPTP passthrough works around this by using a Call ID as a stand-in, so the router can still track the session.

L2TP Passthrough

L2TP is usually paired with IPsec for encryption, and that extra layer can make the traffic harder for NAT to handle normally. It’s still a very outdated protocol, and while it’s a bit more secure than PPTP, it comes with plenty of baggage of its own.

If, for some reason, your setup still uses L2TP/IPsec, the router may have trouble tracking that connection through NAT, which can cause the VPN to fail or break mid-connection.

L2TP/IPsec passthrough solves that by telling the router, “Actually, this is valid VPN traffic. Let it through.”

IPsec Passthrough

IPsec may be an older VPN protocol, but it's still going strong, especially in enterprise setups. Out of the three passthrough types, it's the most complex, but also the most useful today, mostly thanks to its strong encryption.

The issue is that NAT needs to read certain parts of network traffic so it can send it to the right device. IPsec can hide or protect that information (precisely because of how its encryption works), which makes it harder for NAT to process the connection properly. As a result, the router may block it or break it.

IPsec passthrough helps the router handle IPsec traffic without getting confused. It usually does this through NAT-T, which wraps IPsec packets inside UDP packets on port 4500 so NAT can route them normally.

VPN Passthrough vs. VPN Router

But wait a hot minute… what about a VPN router? Isn’t that the same thing as VPN passthrough? We’re glad you asked, and no, it’s not the same thing. 

A VPN passthrough is a router feature (keyword: feature) that allows the VPN traffic on older protocols (PPTP, L2TP, and IPsec) to pass through the router. The router itself isn’t running a VPN. It just sits there, deciding which type of traffic passes through. 

A VPN router, on the other hand, is… well, exactly what it implies: it’s a router that has a VPN installed on it. The router itself establishes and manages the VPN connection, and all devices connected to it are protected by that VPN connection without the need for individual apps.

What about Windscribe, though? Well, Windscribe is a standalone VPN app, but we also support router-level VPN configuration for routers running modern protocols, like OpenVPN, IKEv2, or WireGuard.

Do You Need VPN Passthrough?

No, you most likely don’t. If you’re using a modern VPN app with WireGuard, OpenVPN, or IKEV2, which is most people, you don’t need VPN passthrough, because these protocols can handle NAT natively (translation: they can communicate with your router without extra help). But there are three very specific scenarios when you might need it. 

1. You’re using a legacy corporate VPN.

Some older business VPN setups still rely on IPsec, and if that connection is not using NAT-T, your router may have trouble handling it properly. That is where VPN passthrough can help keep the connection from failing.

2. You’re manually setting up PPTP or L2TP on very old hardware.

Those protocols are outdated, but they still show up in older offices, old routers, and the occasional cursed IT environment that time forgot.

3. You’re troubleshooting VPN problems on a restrictive network.

If you’re troubleshooting VPN problems on a restrictive network, like a hotel, school, or corporate Wi-Fi, VPN passthrough may be worth checking just to make sure the router isn’t blocking an older VPN connection.

How to Enable or Disable VPN Passthrough on Your Router

While every manufacturer uses a different interface, the process for managing these settings is generally consistent across most hardware. Follow these steps to locate the toggles on your device:

1. Access your admin panel: Open a web browser and enter your router’s IP address (typically 192.168.1.1 or 192.168.0.1). Log in with your admin credentials.
2. Locate security settings: Navigate to the section labeled Security, Firewall, VPN, or Advanced Settings.
3. Find the Passthrough toggles: Look for a sub-menu titled VPN Passthrough or ALG. You will likely see individual toggles for PPTP, L2TP, and IPsec.
4. Adjust and save: Enable or disable the protocols as needed, then save your changes. Note that some routers may require a quick reboot to apply the new configuration.

If you’re having trouble finding the menu, check these specific paths for popular brands:

• Linksys: Security > VPN Passthrough
• Netgear: Advanced > Setup > WAN Setup > VPN Passthrough
• TP-Link: Advanced > NAT Forwarding > ALG (or VPN Passthrough)
• Asus: Advanced Settings > VPN > VPN Passthrough
• Cisco SMB: VPN > VPN Passthrough

If you exclusively use modern protocols like WireGuard or OpenVPN, it’s best to disable PPTP passthrough to reduce your network's attack surface.

However, you should generally keep IPsec passthrough enabled if you or anyone on your network uses a corporate VPN, as many work-from-home setups still rely on it.

VPN Passthrough Security Considerations

VPN passthrough itself isn’t automatically a security problem. It doesn’t open your router to all kinds of random traffic, and it doesn’t turn off your firewall. It only helps certain types of VPN traffic get through, while your router continues filtering normal traffic the way it usually does.

The bigger issue is which protocols you’re allowing through. PPTP is old, broken, and full of known security flaws. So while PPTP passthrough isn’t dangerous in some magical, standalone way, leaving it enabled does make it possible for someone on your network to use a weak, outdated protocol that should have been retired ages ago.

That’s why the safest move is usually the simplest one: if you’re not using legacy VPN protocols, turn their passthrough settings off. PPTP passthrough is the clearest example.

There’s no good reason to leave an outdated feature enabled if you don’t need it. It just adds unnecessary attack surface, and unused network features rarely age like fine wine.

The safest approach is to use modern VPN protocols that handle NAT on their own and disable passthrough for protocols you don’t use.

Frequently Asked Questions