Palo's VPN native client is GlobalProtect, it really depends on what OTP vendor you are using to determine if it will function with it. They don't have a Web only client, you would need to use GlobalProtect. VPN functionality is free as long as you don't go past one Portal and one Gateway I believe that there is no user limit as long as your device can handle it. Which firewall you should purchase is based on the number of clients; I would really read up on GlobalProtect on Palo Alto's main website to determine if this fits what you are looking to do. Side Note: If the only thing you are doing is VPN on a Palo product and you aren't going to be using HIP checking, applicaiton ID, or any of the major Palo selling points I'm not sure why you would pick up a Palo product. Setting it to the side of your network and using it as a VPN only device you lose everything that makes Palo products worth the price. In this case I would probably recommend an actual VPN Appliance or a cheap ASA 5505 if it was going to be used only for VPN.
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