IPsec: Setup OPNsense for IKEv1 using XAuth

XAuth was an addition to IKEv1 supporting user authentication credentials additionally to pre-shared keys or certificates. There are three different types supported by OPNsense which we will describe here.

Mutual PSK + XAuth: You define a pre-shared key which is the same for every user and after securing the channel the user authentication via XAuth comes into play. Mutual RSA + XAuth: Instead of using a pre-shared key, every device needs a client certificate to secure the connection plus XAuth for authentication. This is the most secure variant for IKEv1/XAuth but also with the most work to do. Hybrid RSA + XAuth: Hybrid RSA is the same as Mutual, without the need for a client certificate. Only the server will be authenticated (like using HTTPS) to prevent man-in-the-middle attacks like with Mutual PSK. It is more secure than PSK but does not need the complete roll-out process like with Mutual RSA.

We assume you have read the first part at IPsec: Setup Remote Access

Step 1 - Create Certificates (only for RSA variants)

For Mutual RSA + XAuth and Hybrid RSA + XAuth you need to create a Root CA and a server certificate for your Firewall.

Go to System ‣ Trust ‣ Authorities and click Add. Give it a Descriptive Name and as Method choose Create internal Certificate Authority. Increase the Lifetime and fill in the fields matching your local values. Now go to System ‣ Trust ‣ Certificates and create a new certificate for the Firewall itself. Important is to change the Type to server. The Common Name can be the hostname of the Firewall and set as Alternative Name the FQDN your Firewall how it is known to the WAN side. This is most important as your VPN will drop when the FQDN does not match the ones of the certificate.

If you already have a CA roll out a server certificate and import the CA itself via System ‣ Trust ‣ Authorities and the certificate with the key in System ‣ Trust ‣ Certificates.

Step 2 - Mobile Clients

First we will need to setup the mobile clients network and authentication source. Go to VPN ‣ IPsec ‣ Mobile Clients

For our example will use the following settings:

IKE Extensions

Enable checked check to enable mobile clients
User Authentication Local Database For the example we use the Local Database
Group Authentication none Leave on none
Virtual Address Pool 10.10.0.0/24 Enter the IP range for the remote clients

You can select other options, but we will leave them all unchecked for this example.

Save your settings and select Create Phase1 when it appears. Then enter the Mobile Client Phase 1 setting.

Step 3 - Phase 1 Mobile Clients

Phase 1 General information

Connection method default default is ‘Start on traffic’
Key Exchange version V1 XAuth only works on V1
Internet Protocol IPv4  
Interface WAN choose the interface connected to the internet
Description MobileIPsec freely chosen description

Phase 1 proposal (Authentication)

Authentication method XAuth Choose one of the three available options
Negotiation mode Main Mode Use Main Mode here
My identifier Distinguished Name Set the FQDN you used within certificate, for PSK use “My IP address”
Pre-shared Key Shared secret For Mutual PSK + XAuth use this PSK, otherwise certificate below
My Certificate Certificate Choose the certificate from dropdown list, only valid for RSA variants

Phase 1 proposal (Algorithms)

Encryption algorithm AES For our example we will use AES/256 bits
Hash algoritm SHA1, SHA256 SHA1 and SHA256 for compatibility
DH key group 1024, 2048 bit 1024 and 2048 bit for compatibility
Lifetime 28800 sec lifetime before renegotiation

Advanced Options are fine by default.

Save your settings.

Step 3 - Phase 2 Mobile Clients

Press the button that says ‘+ Show 0 Phase-2 entries’

../../_images/ipsec_s2s_vpn_p1a_show_p2.png

You will see an empty list:

../../_images/ipsec_s2s_vpn_p1a_p2_empty.png

Now press the + at the right of this list to add a Phase 2 entry.

General information

Mode Tunnel IPv4 Select Tunnel mode
Description MobileIPsecP2 Freely chosen description

Local Network

Local Network LAN subnet Route the local LAN subnet

Phase 2 proposal (SA/Key Exchange)

Protocol ESP Choose ESP for encryption
Encryption algorithms AES / 256 For this example we use AES 256
Hash algorithms SHA1, SHA256 Same as before, mix SHA1 and SHA256
PFS Key group off Most mobile systems do not support PFS in Phase2
Lifetime 3600 sec  

Save your settings and Enable IPsec, Select:

../../_images/ipsec_s2s_vpn_p1a_enable.png

Note

If you already had IPsec enabled and added Road Warrior setup, it is important to restart the whole service via services widget in the upper right corner of IPSec pages or via System ‣ Diagnostics ‣ Services ‣ Strongswan since applying configuration only reloads it, but a restart also loads the required modules of strongSwan.

Step 4 - Add IPsec Users

Go to System ‣ Access ‣ Users and press the + sign in the lower right corner to add a new user.

Enter the following into the form:

User Name expert
Password &test!9T

Save to apply.

Step 5 - Add client certificate (for Mutual RSA)

This step is only needed for Mutual RSA + XAuth!

Go to System ‣ Trust ‣ Certificates and create a new client certificate. Just click Add, choose your CA and probably increase the lifetime. Everything else besides the CN can be left default. Give a Common Name and Save. Download the newly created certificate as PKCS12 and export it to you enduser device.