What Is VPN Passthrough? Guide to IPsec, PPTP, L2TP

That checkbox labeled “VPN Passthrough” in your router’s admin panel? It’s not as mysterious as it looks. Most people skip it because there’s rarely a clear explanation of what it actually does. This guide breaks down the feature, explains when it matters, and when you can safely ignore it.

Router models supporting VPN passthrough: Most consumer routers manufactured after 2010 support IPsec and PPTP passthrough ·
VPN protocols affected: IPsec, PPTP, L2TP ·
Default passthrough setting on major brands: TP-Link, Netgear, and ASUS enable it by default from 2020 onward ·
Percentage of VPN users behind NAT: Over 90% of home broadband connections use NAT

The table below summarizes the core facts about VPN passthrough.

What Is a VPN Passthrough and How Does It Work?

How NAT interacts with VPN traffic

Network Address Translation (NAT) is the technology that lets multiple devices on a home network share a single public IP address. But NAT doesn’t natively understand VPN protocols. When a device behind NAT tries to send an encrypted VPN packet, the router may not know where to forward it. VPN passthrough solves this by recognizing specific protocol headers — ESP for IPsec, GRE for PPTP, and UDP port 1701 for L2TP — and routing them correctly.

As Checkpoint’s SASE Glossary explains, “VPN passthrough is a router feature that allows data encrypted by VPN protocols to pass network firewall filters.” The feature doesn’t create a VPN connection itself; it simply opens the door for traffic created by a VPN client on a device behind the router.

The role of passthrough in allowing encrypted packets

IPsec, for example, uses ESP (Encapsulating Security Payload) which doesn’t have a standard port number. NAT routers normally drop packets that don’t match a known session. Passthrough intercepts these packets and forwards them based on the Security Parameter Index (SPI). Proton’s blog notes that IPsec passthrough often relies on NAT-T (NAT Traversal) and UDP port 4500 to carry encrypted traffic through routers that already understand UDP packets.

What Does VPN Passthrough Do?

Allows VPN client on a device behind router to connect to remote server

When you launch a VPN client on a laptop or phone that’s connected to a home router, the client sends encrypted packets to the VPN provider’s server. If the router doesn’t understand the protocol, the packets may be dropped. Passthrough ensures they get through. TP-Link’s FAQ states: “VPN Passthrough is a feature that allows VPN traffic created by other endpoints to pass through the router.”

Enables inbound VPN connections to a server behind the router

Less common but still relevant: if you host a VPN server on your local network (for remote access to your home), passthrough allows inbound VPN connections from the internet to reach that server. Cisco’s RV-series documentation shows that IPsec, PPTP, and L2TP passthrough can each be disabled individually on supported routers, giving administrators precise control.

What this means: for most people, the passthrough setting is a “set and forget” toggle. It’s not a performance feature; it’s a compatibility layer.

Should I Disable VPN Passthrough?

When to disable to improve security

Disabling passthrough blocks the corresponding VPN protocols at the router level. If you don’t use IPsec, PPTP, or L2TP — and you want to ensure no device on your network can use them — turning off passthrough adds a layer of security. Palo Alto Networks notes that PPTP has known security weaknesses, so disabling PPTP passthrough is a reasonable precaution.

However, Surfshark’s blog points out that modern routers handle passthrough automatically, and “if you are using a good VPN, you generally do not need to worry about passthrough settings.” The trade-off: disabling passthrough may block a work VPN that relies on IPsec, causing connectivity issues.

When the setting is irrelevant

If all your VPN connections use OpenVPN (UDP 1194) or WireGuard (UDP 51820), passthrough doesn’t come into play. These protocols are NAT-friendly by design. InstaSafe’s comparison categorizes IPsec, L2TP, and PPTP as “legacy or older protocols” associated with passthrough settings. For anyone using a modern VPN provider, the setting is essentially a relic.

What Is IPsec Passthrough and How Is It Different?

IPsec passthrough specifics

IPsec passthrough is a subset of the broader VPN passthrough feature. It specifically handles ESP (IP protocol 50) and IKE (UDP 500/4500) packets. Proton’s guide explains that IPsec passthrough uses NAT-T to encapsulate ESP in UDP packets, allowing them to traverse NAT. Without it, IPsec VPNs fail behind a router that performs NAT.

Some routers label the setting “IPsec Passthrough” separately from “PPTP Passthrough” and “L2TP Passthrough.” DrayTek’s support documentation shows that on some models, you can enable or disable IPsec passthrough via a CLI command: srv nat ipsecpass on.

IPsec passthrough on or off for gaming

Gaming consoles like PlayStation and Xbox use IPsec for voice chat and matchmaking in some titles. If you disable IPsec passthrough, you may experience voice chat failures or inability to join certain multiplayer sessions. Cisco’s documentation confirms that IPsec passthrough can be toggled independently, so gamers can keep it enabled while disabling PPTP passthrough for security.

The pattern: IPsec passthrough is the protocol most likely to be needed for real-world scenarios beyond pure VPN usage. Disabling it may break more than just corporate VPNs.

What About L2TP and PPTP Passthrough?

L2TP passthrough and when to enable

L2TP (Layer 2 Tunneling Protocol) uses UDP port 1701. It’s often paired with IPsec for encryption. Palo Alto Networks describes L2TP as “more secure than PPTP, which has known security weaknesses.” L2TP passthrough allows the router to maintain the session ID and route the traffic through NAT. Most modern routers enable L2TP passthrough by default, so you rarely need to touch it.

PPTP passthrough and its security risks

PPTP (Point-to-Point Tunneling Protocol) uses GRE (Generic Routing Encapsulation) and is widely considered insecure. Checkpoint notes that PPTP passthrough enables the protocol, but security experts recommend disabling it unless you have a legacy device that requires it. DrayTek shows that to disable PPTP services entirely, you go to VPN and Remote Access > Remote Access Control on their routers.

The trade-off: keeping PPTP passthrough enabled exposes your network to a protocol with known vulnerabilities. Disabling it eliminates that risk without affecting modern VPNs.

What’s Confirmed and What’s Unclear

Confirmed facts

• VPN passthrough forwards protocol-specific packets (ESP, GRE, UDP 1701) through NAT (Checkpoint SASE Glossary)
• Disabling passthrough blocks those protocols at the router level (Cisco documentation)
• Most routers have passthrough enabled by default (Surfshark blog)
• Modern VPN protocols (OpenVPN, WireGuard) do not require passthrough (Proton blog)

What’s unclear

• Exactly which router models ship with passthrough disabled by default
• Whether disabling passthrough provides a meaningful security improvement in a typical home network

“A VPN passthrough is a router feature that allows data encrypted by VPN protocols to pass network firewall filters.”

— NordLayer support article

“VPN Passthrough is a feature that allows VPN traffic created by other endpoints to pass through the router.”

— TP-Link FAQ

For anyone maintaining a home network in 2025, the choice is straightforward: leave passthrough enabled unless you have a specific reason to disable it. If you’re using a modern VPN client, the setting won’t affect your internet speed or security. But if you’re running a corporate IPsec VPN or hosting a VPN server, that small checkbox is the difference between a working connection and a frustrating error message.

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