Overview

This article describes how to set up an L2TP VPN using the UniFi Security Gateway (USG) as a RADIUS Server.

NOTES & REQUIREMENTS:

L2TP VPN is designed to only work on WAN 1.

Please complete the prerequisite configuration found in the UniFi - USG: Configuring RADIUS Server article before following this guide's instructions.

Devices Used:

UniFi Controller Setup

1. Navigate to Settings > Networks > Create New Network in the UniFi Controller.

2. Fill out the necessary fields as shown in the image above:

Purpose: Remote User VPN
VPN Type: L2TP Server
Pre-Shared Key: Known as the pre-shared secret, will be entered along with the username and password (created in RADIUS users) on L2TP clients.
Gateway/Subnet: Will need to be non-conflicting with any other networks present on the controller.
Nameserver and WINS servers: Can be left auto/blank, unless further customizing the configuration is desired.
Site-to-Site VPN: If you're using the "Auto" VPN type to connect sites, the L2TP VPN subnet will be included in those automatic routes if this option is selected.

3. Choose the Default RADIUS Profile from the drop-down.

4. Click SAVE.

If using a Windows machine to connect to L2TP, follow these steps to set it up:

1. Go to Settings

2. VPN > Add VPN connection

3. See the following screenshot and fill the information requested.

Windows Authentication Setup

Go to Control Panel > Network & Sharing settings > Change Adapter Settings.
Right-click the L2TP adapter, then go to Properties > Security.
Under Type of VPN, select Layer 2 Tunneling Protocol with IPsec.
Click Advanced Settings. Select preshared key for authentication and enter it.
Make sure to have the option of Allow these protocols enabled and mark the checkbox for Check Microsoft CHAP Version 2 (MS-CHAP v2), as shown in the screenshot below.

The macOS setup is more straightforward and no authentication modifications are needed.

1. Simply go to System Preferences > Network

2. Click the + button

2.1 Interface: VPN

2.2 VPN Type: L2TP over IPsec

3. In Authentication settings enter the preshared key.

L2TP doesn't have a route distribution method. If the setting on the client device to route "all" traffic through the tunnel is not enabled, it will be necessary to add the manual routes on the client, to point to the USG's local networks. Search in each specific client device's documentation on how to enable sending all traffic over the VPN connection.
Setting up L2TP will auto add firewall rules to WAN Local in Settings > Routing & Firewall, no manual rules are required on the user end.
If your USG's WAN is behind NAT and has a private IP, it is necessary to configure port forwarding on the upstream router to forward UDP ports 500, 1701, and 4500 to the USG's WAN address.
In pre-4.3.41 USG firmware, L2TP remote access VPN will not work if there are already one or more site-to-site IPsec VPNs configured. Please update to the latest firmware.
In controller versions prior to 5.7.22, if UPnP is configured on the USG, an ACL will need to be created to deny UDP ports 500/4500. See this Community post for more. This community post is in the Early access section of our Community, see this article to learn How to Sign Up for Early Access.