VPN for remote access to home LAN (IPSec?)

Question

Another probably daft question: I am in the process of setting up a VPN connection for the purpose of remote access to services on my home LAN. The router, firewall and VPN server i am using for this is a Draytek Vigor 2865. My biggest problem here is choosing a VPN protocol/understanding IPSec.

I have successfully setup a PPTP VPN, which works fine. Draytek setup as server, a couple of user accounts on the Draytek with unique usernames and passwords which can be used to connect to the VPN, and i can change various settings on a user based basis. (I.E i could assign specific dial-in users a specific IP). However, i know PPTP is not the most secure option. Really, for my needs, PPTP with maximum MPPE encryption and strong passwords would probably be fine, but i would rater use the better option if it is available.

Here are the dial-in options in the draytek: VPN options in the Draytek

Obviously, i am trying to avoid PPTP. I don't want to use OpenVPN, because i need to be able to use the built in Windows VPN client, and i don't think, from what i understand, SSL VPN is what i want here either. That leaves IPsec tunnel or L2TP (With IPsec).

What i really don't understand about IPSec is that it seems to use a "Pre shared key" for authentication, and i don't quite know how this works. Does every remote user login with the same PSK? In which case how can you distinguish remote users on the server end? It would make sense if a PSK was used IN ADDITION to a user/pass, but in some cases it seems just a PSK is used... (Example of this: https://draytek.co.uk/support/guides/kb-teleworker-smartvpn-ipsec)

Would you recommend the IPsec tunnel option, or is L2TP with IPsec nice and secure? Which option does the Windows VPN client support?

Sorry for the long post, any advice would be appreciated.

Answer 1

What i really don't understand about IPSec is that it seems to use a "Pre shared key" for authentication, and i don't quite know how this works. Does every remote user login with the same PSK? In which case how can you distinguish remote users on the server end?

In the original protocol (IKEv1), you indeed cannot. (Though it's not strictly true that it always uses a PSK – certificates are preferred, and do allow distinguishing users by the certificate's metadata.)

This omission was solved in several different ways:

1. Cisco added a custom modification for their "IPsec VPN" to allow user/password authentication as a second step (and I think they renamed the PSK to "Group key"). That's the "Xauth" option in your router.

   I'm not sure what apps you'd use to connect to Xauth VPNs from Windows (there's strongSwan on Linux and Android).

2. Microsoft instead chose to tunnel another VPN protocol inside the IPsec-secured tunnel – the IPsec PSK is used to protect L2TP, which then allows performing the same PAP/MSCHAP/EAP authentication as in PP(T)P. That's "L2TP with IPsec Policy" in your router.

   Windows has this built in, but since it's two different protocols tied together, Linux setup can get complex.

3. Finally, the newer protocol version – IKEv2 – has built-in solutions. First, clients can send an "initiator ID (IDi)" which acts nearly as a user name; different initiators can have different PSKs (or even completely different configurations).

   Second, IKEv2 natively supports EAP auth including MSCHAPv2, which will also transmit usernames as part of EAP. (This is essentially the Xauth extension made official.)

   Windows 10+ has built-in client support for IKEv2; for Android I'd use the strongSwan app.

(Another thing missing from stock IKEv1 is automatic assignment of client IPs, which is also added by all of the above extensions.)

Would you recommend the IPsec tunnel option, or is L2TP with IPsec nice and secure? Which option does the Windows VPN client support?

IKEv2 is the modern choice, where supported – I would pick "IKEv2 EAP" if I needed different user accounts, as that's what Windows supports.

Anything that's built on IKEv1 is a bit stale, and I think the PSK in IKEv1 directly contributes to the encryption of the tunnel, so it must be strong – not a password but a random key or passphrase. Still, if set up properly, it is more secure than MPPE.

(I wouldn't worry about it using MSCHAPv2 – in all of the above modes, user authentication is done inside an already encrypted tunnel, unlike with PPTP which did it in the clear, so it could as well be just a regular password and it'd still be secure.)

and i don't think, from what i understand, SSL VPN is what i want here either

That depends. "SSL VPN" is not a single protocol, it's a very broad description for many different products that involve SSL (TLS, DTLS) as their basis, but usually in different ways. For example, Cisco AnyConnect is an "SSL VPN" product but it's not compatible with any other "SSL VPN" except itself.

In fact, Microsoft itself has a TLS-based VPN protocol – SSTP – which is natively supported by Windows and is overall fairly secure; as secure as a regular TLS connection, that is. So if you have that as an option you could certainly use it instead of IKEv2. (Though it has a small downside in that it's TCP-based; TCP-inside-TCP is not ideal.)