User's Manual

https://www.peplink.com 20 Copyright @ 2021 Peplink
4.5 USBModemandAndroidTethering 
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For increased WAN diversity, plug in a USB LTE modem as backup. Peplink routers are compatible with
over 200 modem types. You can also tether to smartphones running Android 4.1.X and above.
By default, the USB port is “USB Modem” mode. If you need to use it to connect to USB Ethernet Adapter,
you need to change it to “USB Ethernet” mode,
https://forum.peplink.com/t/can-i-use-ethernet-adapters-on-the-usb-wan/8327
4.6 Built‐InRemoteUserVPNSupport 
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Use OpenVPN or L2TP with IPsec to safely and conveniently connect remote clients to your private
network. L2TP with IPsec is supported by most devices, but legacy devices can also connect using PPTP.
Click here for the full instructions on setting up L2TP with IPsec.
Click here for the full instructions on setting up OpenVPN connections