setup-ipsec-vpn/docs/ikev2-howto.md

How-To: IKEv2 VPN for Windows and Android

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

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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 contains improvements such as Standard Mobility support through MOBIKE, and improved reliability. In addition, IKEv2 supports connecting multiple devices simultaneously from behind the same NAT (e.g. home router) to the VPN server.

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:

• Windows 7, 8.x and 10
• strongSwan Android VPN client

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, and upgraded Libreswan to the latest version.

1. Find the VPN server's public IP, save it to a variable and check.

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

   Note: Alternatively, you may specify the server's DNS name here. e.g. PUBLIC_IP=myvpn.example.com.

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
     rightid=%fromcert
     rightaddresspool=192.168.43.10-192.168.43.250
     rightca=%same
     rightrsasigkey=%cert
     narrowing=yes
     dpddelay=30
     dpdtimeout=120
     dpdaction=clear
     auto=add
     ikev2=insist
     rekey=no
     fragmentation=yes
     ike=3des-sha1,3des-sha2,aes-sha1,aes-sha1;modp1024,aes-sha2,aes-sha2;modp1024
     phase2alg=3des-sha1,3des-sha2,aes-sha1,aes-sha2
   EOF
   

   We need to add a few more lines to that file. First check your Libreswan version, then run one of the following commands:

   $ ipsec --version
   

   For Libreswan 3.23 and newer:

   $ cat >> /etc/ipsec.conf <<EOF
     modecfgdns="8.8.8.8, 8.8.4.4"
     encapsulation=yes
   EOF
   

   For Libreswan 3.19-3.22:

   $ cat >> /etc/ipsec.conf <<EOF
     modecfgdns1=8.8.8.8
     modecfgdns2=8.8.4.4
     encapsulation=yes
   EOF
   

   For Libreswan 3.18 and older:

   $ cat >> /etc/ipsec.conf <<EOF
     modecfgdns1=8.8.8.8
     modecfgdns2=8.8.4.4
     forceencaps=yes
   EOF
   

3. Generate Certificate Authority (CA) and VPN server certificates:

   Note: Specify the certificate validity period (in months) with "-v". e.g. "-v 36". Also, if you used the server's DNS name instead of its IP address in step 1 above, replace --extSAN "ip:$PUBLIC_IP,dns:$PUBLIC_IP" in the command below with --extSAN "dns:$PUBLIC_IP".

   $ certutil -z <(head -c 1024 /dev/urandom) \
     -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
   
     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 -z <(head -c 1024 /dev/urandom) \
     -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"
   
     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 -z <(head -c 1024 /dev/urandom) \
     -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"
   
     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 to generate certificates for additional VPN clients. Replace every vpnclient with vpnclient2, etc.

   Note: 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 VPN connection, and enjoy your IKEv2 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 Select user certificate, then tap Install certificate.
   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.

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

1. The built-in VPN client in Windows may not support IKEv2 fragmentation. On some networks, this can cause the connection to fail or have other issues. You may instead try the IPsec/L2TP or IPsec/XAuth mode.
2. If using the strongSwan Android VPN client, you must upgrade Libreswan on your server to version 3.26 or above.

References

• https://libreswan.org/wiki/VPN_server_for_remote_clients_using_IKEv2
• https://libreswan.org/wiki/HOWTO:_Using_NSS_with_libreswan
• https://libreswan.org/man/ipsec.conf.5.html
• https://wiki.strongswan.org/projects/strongswan/wiki/WindowsClients
• https://wiki.strongswan.org/projects/strongswan/wiki/AndroidVpnClient