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How-To: IKEv2 VPN for Windows 7 and newer

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.

First, make sure you have successfully set up your VPN server. Commands below must be run as root.

  1. Find the public and private IP of your server, and make sure they are not empty. It is OK if they are the same.

    $ PUBLIC_IP=$(dig @resolver1.opendns.com -t A -4 myip.opendns.com +short)
    $ PRIVATE_IP=$(ip -4 route get 1 | awk '{print $NF;exit}')
    $ echo "$PUBLIC_IP"
    (Your public IP is displayed)
    $ echo "$PRIVATE_IP"
    (Your private IP is displayed)
  2. Add a new IKEv2 connection to /etc/ipsec.conf:

    $ cat >> /etc/ipsec.conf <<EOF
    
    conn ikev2-cp
      left=$PRIVATE_IP
      leftcert=$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
      forceencaps=yes
      ike=3des-sha1,aes-sha1,aes256-sha2_512,aes256-sha2_256
      phase2alg=3des-sha1,aes-sha1,aes256-sha2_512,aes256-sha2_256
    EOF
  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 ",," -1 -6 -8 "$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...
    
                    0 - Digital Signature
                    1 - Non-repudiation
                    2 - Key encipherment
                    3 - Data encipherment
                    4 - Key agreement
                    5 - Cert signing key
                    6 - CRL signing key
                    Other to finish
     > 0
                    0 - Digital Signature
                    1 - Non-repudiation
                    2 - Key encipherment
                    3 - Data encipherment
                    4 - Key agreement
                    5 - Cert signing key
                    6 - CRL signing key
                    Other to finish
     > 2
                    0 - Digital Signature
                    1 - Non-repudiation
                    2 - Key encipherment
                    3 - Data encipherment
                    4 - Key agreement
                    5 - Cert signing key
                    6 - CRL signing key
                    Other to finish
     > 8
    Is this a critical extension [y/N]?
    N
                    0 - Server Auth
                    1 - Client Auth
                    2 - Code Signing
                    3 - Email Protection
                    4 - Timestamp
                    5 - OCSP Responder
                    6 - Step-up
                    7 - Microsoft Trust List Signing
                    Other to finish
     > 0
                    0 - Server Auth
                    1 - Client Auth
                    2 - Code Signing
                    3 - Email Protection
                    4 - Timestamp
                    5 - OCSP Responder
                    6 - Step-up
                    7 - Microsoft Trust List Signing
                    Other to finish
     > 8
    Is this a critical extension [y/N]?
    N
  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 ",," -1 -6 -8 "vpnclient"
    
    -- repeat same extensions as above --
    
    $ 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.

  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 delete a certificate, use certutil -D -d sql:/etc/ipsec.d -n "Certificate Nickname".

  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

    Import the .p12 file to the Computer certificate store. The CA cert once imported must be placed into the "Certificates" sub-folder under "Trusted Root Certification Authorities".

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

    On the Windows computer, add a new IKEv2 VPN connection:

    https://wiki.strongswan.org/projects/strongswan/wiki/Win7Config

    Start the new IKEv2 VPN connection, and enjoy your own VPN!

    https://wiki.strongswan.org/projects/strongswan/wiki/Win7Connect

    Windows Phone 8.1 and above

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

    Android 4.x and newer

    Please refer to: https://wiki.strongswan.org/projects/strongswan/wiki/AndroidVpnClient

    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 7 and newer does not support IKEv2 fragmentation. On some networks, this can cause the connection to fail with "Error 809", or you may be unable to open any website after connecting. If this happens, first try this workaround. If it doesn't work, please connect using IPsec/L2TP or IPsec/XAuth mode instead.

References