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How-To: IKEv2 VPN for Windows and Android

Read this in other languages: English, 简体中文.

IMPORTANT: This guide is for advanced users only. Other users please use IPsec/L2TP or IPsec/XAuth.

Windows 7 and newer releases support the IKEv2 standard through Microsoft's Agile VPN functionality. Internet Key Exchange (IKE or IKEv2) is the protocol used to set up a Security Association (SA) in the IPsec protocol suite. Compared to IKE version 1, IKEv2 has multiple improvements such as Standard Mobility support through MOBIKE, and improved reliability.

Libreswan can authenticate IKEv2 clients on the basis of X.509 Machine Certificates using RSA signatures. This method does not require an IPsec PSK, username or password. It can be used with:

The following example shows how to configure IKEv2 with Libreswan. Commands below must be run as root.

Before continuing, make sure you have successfully set up your VPN server.

  1. Find the public IP of your server, and make sure it is correct.

    $ PUBLIC_IP=$(wget -t 3 -T 15 -qO- http://ipv4.icanhazip.com)
$ echo "$PUBLIC_IP"
(Check the displayed public IP)

  2. Add a new IKEv2 connection to /etc/ipsec.conf:

    $ cat >> /etc/ipsec.conf <<EOF

conn ikev2-cp
  left=%defaultroute
  leftcert=$PUBLIC_IP
  leftid=@$PUBLIC_IP
  leftsendcert=always
  leftsubnet=0.0.0.0/0
  leftrsasigkey=%cert
  right=%any
  rightaddresspool=192.168.43.10-192.168.43.250
  rightca=%same
  rightrsasigkey=%cert
  modecfgdns1=8.8.8.8
  modecfgdns2=8.8.4.4
  narrowing=yes
  dpddelay=30
  dpdtimeout=120
  dpdaction=clear
  auto=add
  ikev2=insist
  rekey=no
  fragmentation=yes
  ike=3des-sha1,3des-sha1;modp1024,aes-sha1,aes-sha1;modp1024,aes-sha2,aes-sha2;modp1024
  phase2alg=3des-sha1,aes-sha1,aes-sha2
EOF

    We need to add one more line to that file. First check your Libreswan version:

    $ ipsec --version

    For Libreswan 3.19 and newer, run command:

    $ echo " encapsulation=yes" >> /etc/ipsec.conf

    For Libreswan 3.18 and older, run command:

    $ echo " forceencaps=yes" >> /etc/ipsec.conf

  3. Generate Certificate Authority (CA) and VPN server certificates:
    Note: Specify the certificate validity period (in months) using "-v". e.g. "-v 36".

    $ certutil -S -x -n "Example CA" -s "O=Example,CN=Example CA" -k rsa -g 4096 -v 36 -d sql:/etc/ipsec.d -t "CT,," -2

A random seed must be generated that will be used in the
creation of your key.  One of the easiest ways to create a
random seed is to use the timing of keystrokes on a keyboard.

To begin, type keys on the keyboard until this progress meter
is full.  DO NOT USE THE AUTOREPEAT FUNCTION ON YOUR KEYBOARD!

Continue typing until the progress meter is full:

|************************************************************|

Finished.  Press enter to continue:

Generating key.  This may take a few moments...

Is this a CA certificate [y/N]?
y
Enter the path length constraint, enter to skip [<0 for unlimited path]: >
Is this a critical extension [y/N]?
N

$ certutil -S -c "Example CA" -n "$PUBLIC_IP" -s "O=Example,CN=$PUBLIC_IP" -k rsa -g 4096 -v 36 -d sql:/etc/ipsec.d -t ",," \
   --keyUsage digitalSignature,keyEncipherment --extKeyUsage serverAuth --extSAN "ip:$PUBLIC_IP,dns:$PUBLIC_IP"

A random seed must be generated that will be used in the
creation of your key.  One of the easiest ways to create a
random seed is to use the timing of keystrokes on a keyboard.

To begin, type keys on the keyboard until this progress meter
is full.  DO NOT USE THE AUTOREPEAT FUNCTION ON YOUR KEYBOARD!

Continue typing until the progress meter is full:

|************************************************************|

Finished.  Press enter to continue:

Generating key.  This may take a few moments...

  4. Generate client certificate(s), and export the .p12 file that contains the client certificate, private key, and CA certificate:

    $ certutil -S -c "Example CA" -n "vpnclient" -s "O=Example,CN=vpnclient" -k rsa -g 4096 -v 36 -d sql:/etc/ipsec.d -t ",," \
   --keyUsage digitalSignature,keyEncipherment --extKeyUsage serverAuth,clientAuth -8 "vpnclient"

A random seed must be generated that will be used in the
creation of your key.  One of the easiest ways to create a
random seed is to use the timing of keystrokes on a keyboard.

To begin, type keys on the keyboard until this progress meter
is full.  DO NOT USE THE AUTOREPEAT FUNCTION ON YOUR KEYBOARD!

Continue typing until the progress meter is full:

|************************************************************|

Finished.  Press enter to continue:

Generating key.  This may take a few moments...

$ pk12util -o vpnclient.p12 -n "vpnclient" -d sql:/etc/ipsec.d

Enter password for PKCS12 file:
Re-enter password:
pk12util: PKCS12 EXPORT SUCCESSFUL

    Repeat this step for additional VPN clients, but replace every vpnclient with vpnclient2, etc.

    Note: If you wish to connect multiple VPN clients simultaneously, you must generate a unique certificate for each.

  5. The database should now contain:

    $ certutil -L -d sql:/etc/ipsec.d

Certificate Nickname                               Trust Attributes
                                                   SSL,S/MIME,JAR/XPI

Example CA                                         CTu,u,u
($PUBLIC_IP)                                       u,u,u
vpnclient                                          u,u,u

    Note: To display a certificate, use certutil -L -d sql:/etc/ipsec.d -n "Nickname". To delete a certificate, replace -L with -D. For other certutil usage, read this page.

  6. Restart IPsec service:

    $ service ipsec restart

  7. The vpnclient.p12 file should then be securely transferred to the VPN client device. Next steps:

    Windows 7, 8.x and 10

    1. Import the .p12 file to the "Computer account" certificate store. Make sure that the client cert is placed in "Personal -> Certificates", and the CA cert is placed in "Trusted Root Certification Authorities -> Certificates".

      Detailed instructions:
      https://wiki.strongswan.org/projects/strongswan/wiki/Win7Certs

    2. On the Windows computer, add a new IKEv2 VPN connection：
      https://wiki.strongswan.org/projects/strongswan/wiki/Win7Config

    3. Start the new IKEv2 VPN connection, and enjoy your VPN!
      https://wiki.strongswan.org/projects/strongswan/wiki/Win7Connect

    4. (Optional) You may enable stronger ciphers by adding this registry key and reboot.

    Android 4.x and newer

    1. Install strongSwan VPN Client from Google Play.
    2. Launch the VPN client and tap Add VPN Profile.
    3. Enter Your VPN Server IP in the Server field.
    4. Select IKEv2 Certificate from the VPN Type drop-down menu.
    5. Tap to add a User certificate, then tap Install.
    6. Choose the .p12 file you copied from the VPN server, and follow the prompts.
    7. Save the new VPN connection, then tap to connect.

    Windows Phone 8.1 and above

    First import the .p12 file, then follow these instructions to configure a certificate-based IKEv2 VPN.

  8. Once successfully connected, you can verify that your traffic is being routed properly by looking up your IP address on Google. It should say "Your public IP address is Your VPN Server IP".

Known Issues

The built-in VPN client in Windows does not support IKEv2 fragmentation. On some networks, this can cause the connection to fail or have other issues. You may try this registry fix, or connect using IPsec/L2TP or IPsec/XAuth mode instead.

References