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Guide: How to Set Up and Use IKEv2 VPN

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

Note: You may also connect using IPsec/L2TP or IPsec/XAuth mode.

Introduction

Modern operating systems (such as Windows 7 and newer) support the IKEv2 standard. 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.

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
  • OS X (macOS)
  • iOS (iPhone/iPad)
  • Android 4.x and newer (using the strongSwan VPN client)
  • Linux

After following this guide, you will be able to connect to the VPN using IKEv2 in addition to the existing IPsec/L2TP and IPsec/XAuth ("Cisco IPsec") modes.

Using helper scripts

Important: Before continuing, you should have successfully set up your own VPN server, and (optional but recommended) updated Libreswan. Docker users, see here.

Use this helper script to automatically set up IKEv2 on the VPN server:

sudo bash /opt/src/ikev2.sh --auto

The script must be run using bash, not sh. The command above runs the helper script in auto mode, using default options. Remove the --auto parameter if you want to customize IKEv2 setup options. When finished, continue to configure IKEv2 VPN clients.

Error: "bash: /opt/src/ikev2.sh: No such file or directory".

This is normal if you used an older version of the VPN setup script. Please download and run the IKEv2 helper script using this command:

wget https://git.io/ikev2setup -O /opt/src/ikev2.sh && sudo bash /opt/src/ikev2.sh --auto
You may optionally specify a DNS name, client name and/or custom DNS servers. Click here for details.

When running IKEv2 setup in auto mode, advanced users can optionally specify a DNS name to be used as the VPN server's address. The DNS name must be a fully qualified domain name (FQDN). Example:

sudo VPN_DNS_NAME='vpn.example.com' bash ikev2.sh --auto

Similarly, you may optionally specify a name for the first IKEv2 client. The default is vpnclient if not specified.

sudo VPN_CLIENT_NAME='your_client_name' bash ikev2.sh --auto

By default, IKEv2 clients are set to use Google Public DNS when the VPN is active. When running IKEv2 setup in auto mode, you may optionally specify custom DNS server(s). Example:

sudo VPN_DNS_SRV1=1.1.1.1 VPN_DNS_SRV2=1.0.0.1 bash ikev2.sh --auto
Click here to view usage information for the IKEv2 helper script.
Usage: bash ikev2.sh [options]

Options:
  --auto                        run IKEv2 setup in auto mode using default options (for initial setup only)
  --addclient [client name]     add a new client using default options (after IKEv2 setup)
  --exportclient [client name]  export configuration for an existing client (after IKEv2 setup)
  --listclients                 list the names of existing clients (after IKEv2 setup)
  --removeikev2                 remove IKEv2 and delete all certificates and keys from the IPsec database
  -h, --help                    show this help message and exit

To customize IKEv2 or client options, run this script without arguments.

Configure IKEv2 VPN clients

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

Note: The password for client configuration files can be found in the output of the IKEv2 helper script. If you want to add or export IKEv2 client(s), just run the helper script again. Use option -h to show usage information.

Windows 7, 8.x and 10

  1. Securely transfer the generated .p12 file to your computer, then import it into the "Computer account" certificate store. To import the .p12 file, run the following from an elevated command prompt:

    # Import .p12 file (replace with your own value)
    certutil -f -importpfx "\path\to\your\file.p12" NoExport

    Alternatively, you can manually import the .p12 file. Click here for instructions. Make sure that the client cert is placed in "Personal -> Certificates", and the CA cert is placed in "Trusted Root Certification Authorities -> Certificates".

    Note: Ubuntu 18.04 users may encounter the error "The password you entered is incorrect" when trying to import the .p12 file. See Troubleshooting.

  2. On the Windows computer, add a new IKEv2 VPN connection. For Windows 8.x and 10, it is recommended to create the VPN connection using the following commands from a command prompt, for improved security and performance. Windows 7 does not support these commands, you may manually create the VPN connection (see below).

    # Create VPN connection (replace server address with your own value)
    powershell -command "Add-VpnConnection -ServerAddress 'Your VPN Server IP (or DNS name)' -Name 'My IKEv2 VPN' -TunnelType IKEv2 -AuthenticationMethod MachineCertificate -EncryptionLevel Required -PassThru"
    # Set IPsec configuration
    powershell -command "Set-VpnConnectionIPsecConfiguration -ConnectionName 'My IKEv2 VPN' -AuthenticationTransformConstants GCMAES128 -CipherTransformConstants GCMAES128 -EncryptionMethod AES256 -IntegrityCheckMethod SHA256 -PfsGroup None -DHGroup Group14 -PassThru -Force"

    Alternatively, you can manually create the VPN connection. Click here for instructions. If you specified the server's DNS name (instead of its IP address) during IKEv2 setup, you must enter the DNS name in the Internet address field.

  3. Enable stronger ciphers for IKEv2 with a one-time registry change. This is optional, but recommended. Download and import the .reg file below, or run the following from an elevated command prompt. Read more here.

    • For Windows 7, 8.x and 10 (download .reg file)

      REG ADD HKLM\SYSTEM\CurrentControlSet\Services\RasMan\Parameters /v NegotiateDH2048_AES256 /t REG_DWORD /d 0x1 /f

To connect to the VPN: Click on the wireless/network icon in your system tray, select the new VPN entry, and click Connect. 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".

If you get an error when trying to connect, see Troubleshooting.

OS X (macOS)

First, securely transfer the generated .mobileconfig file to your Mac, then double-click and follow the prompts to import as a macOS profile. When finished, check to make sure "IKEv2 VPN" is listed under System Preferences -> Profiles.

To connect to the VPN:

  1. Open System Preferences and go to the Network section.
  2. Select the VPN connection with Your VPN Server IP (or DNS name).
  3. Check the Show VPN status in menu bar checkbox.
  4. Click Connect.

(Optional feature) You can choose to enable VPN On Demand. This is an "always-on" feature that can automatically connect to the VPN while on Wi-Fi. To enable, check the Connect on demand checkbox for the VPN connection, and click Apply.

If you manually set up IKEv2 without using the helper script, click here for instructions.

First, securely transfer the generated .p12 file to your Mac, then double-click to import into the login keychain in Keychain Access. Next, double-click on the imported IKEv2 VPN CA certificate, expand Trust and select Always Trust from the IP Security (IPsec) drop-down menu. Close the dialog using the red "X" on the top-left corner. When prompted, use Touch ID or enter your password and click "Update Settings".

When finished, check to make sure both the new client certificate and IKEv2 VPN CA are listed under the Certificates category of login keychain.

  1. Open System Preferences and go to the Network section.
  2. Click the + button in the lower-left corner of the window.
  3. Select VPN from the Interface drop-down menu.
  4. Select IKEv2 from the VPN Type drop-down menu.
  5. Enter anything you like for the Service Name.
  6. Click Create.
  7. Enter Your VPN Server IP (or DNS name) for the Server Address.
    Note: If you specified the server's DNS name (instead of its IP address) during IKEv2 setup, you must enter the DNS name in the Server Address and Remote ID fields.
  8. Enter Your VPN Server IP (or DNS name) for the Remote ID.
  9. Enter Your VPN client name in the Local ID field.
    Note: This must match exactly the client name you specified during IKEv2 setup. Same as the first part of your .p12 filename.
  10. Click the Authentication Settings... button.
  11. Select None from the Authentication Settings drop-down menu.
  12. Select the Certificate radio button, then select the new client certificate.
  13. Click OK.
  14. Check the Show VPN status in menu bar checkbox.
  15. Click Apply to save the VPN connection information.
  16. Click Connect.

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".

If you get an error when trying to connect, see Troubleshooting.

iOS

First, securely transfer the generated .mobileconfig file to your iOS device, then import it as an iOS profile. To transfer the file, you may use:

  1. AirDrop, or
  2. Upload to your device using "File Sharing" in iTunes, then open the "Files" app on your iOS device, move the uploaded file to the "On My iPhone" folder. After that, tap the file and go to "Settings" to import, or
  3. Host the file on a secure website of yours, then download and import it in Mobile Safari.

When finished, check to make sure "IKEv2 VPN" is listed under Settings -> General -> Profile(s).

To connect to the VPN:

  1. Go to Settings -> General -> VPN.
  2. Select the VPN connection with Your VPN Server IP (or DNS name).
  3. Slide the VPN switch ON.

(Optional feature) You can choose to enable VPN On Demand. This is an "always-on" feature that can automatically connect to the VPN while on Wi-Fi. To enable, tap the "i" icon on the right of the VPN connection, and enable Connect On Demand.

If you manually set up IKEv2 without using the helper script, click here for instructions.

First, securely transfer the generated ikev2vpnca.cer and .p12 files to your iOS device, then import them one by one as iOS profiles. To transfer the files, you may use:

  1. AirDrop, or
  2. Upload to your device using "File Sharing" in iTunes, then open the "Files" app on your iOS device, move the uploaded files to the "On My iPhone" folder. After that, tap each file and go to "Settings" to import, or
  3. Host the files on a secure website of yours, then download and import them in Mobile Safari.

When finished, check to make sure both the new client certificate and IKEv2 VPN CA are listed under Settings -> General -> Profiles.

  1. Go to Settings -> General -> VPN.
  2. Tap Add VPN Configuration....
  3. Tap Type. Select IKEv2 and go back.
  4. Tap Description and enter anything you like.
  5. Tap Server and enter Your VPN Server IP (or DNS name).
    Note: If you specified the server's DNS name (instead of its IP address) during IKEv2 setup, you must enter the DNS name in the Server and Remote ID fields.
  6. Tap Remote ID and enter Your VPN Server IP (or DNS name).
  7. Enter Your VPN client name in the Local ID field.
    Note: This must match exactly the client name you specified during IKEv2 setup. Same as the first part of your .p12 filename.
  8. Tap User Authentication. Select None and go back.
  9. Make sure the Use Certificate switch is ON.
  10. Tap Certificate. Select the new client certificate and go back.
  11. Tap Done.
  12. Slide the VPN switch ON.

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".

If you get an error when trying to connect, see Troubleshooting.

Android

  1. Securely transfer the generated .sswan file to your Android device.
  2. Install strongSwan VPN Client from Google Play.
  3. Launch the strongSwan VPN client.
  4. Tap the "more options" menu on top right, then tap Import VPN profile.
  5. Choose the .sswan file you transferred from the VPN server.
    Note: To find the .sswan file, tap the three-line menu button, then browse to the location you saved the file.
  6. On the "Import VPN profile" screen, tap IMPORT CERTIFICATE FROM VPN PROFILE, and follow the prompts.
  7. On the "Choose certificate" screen, select the new client certificate, then tap Select.
  8. Tap IMPORT.
  9. Tap the new VPN profile to connect.
If your device runs Android 6.0 or older, click here for additional instructions.

If your device runs Android 6.0 (Marshmallow) or older, in order to connect using the strongSwan VPN client, you must make the following change on the VPN server: Edit /etc/ipsec.d/ikev2.conf on the server. Append authby=rsa-sha1 to the end of the conn ikev2-cp section, indented by two spaces. Save the file and run service ipsec restart.

(Optional feature) You can choose to enable the "Always-on VPN" feature on Android. Launch the Settings app, go to Network & internet -> Advanced -> VPN, click the gear icon on the right of "strongSwan VPN Client", then enable the Always-on VPN and Block connections without VPN options.

If you manually set up IKEv2 without using the helper script, click here for instructions.

Android 10 and newer:

  1. Securely transfer the generated .p12 file to your Android device.
  2. Install strongSwan VPN Client from Google Play.
  3. Launch the Settings application.
  4. Go to Security -> Advanced -> Encryption & credentials.
  5. Tap Install certificates from storage (or SD card).
  6. Choose the .p12 file you transferred from the VPN server, and follow the prompts.
    Note: To find the .p12 file, tap the three-line menu button, then browse to the location you saved the file.
  7. Launch the strongSwan VPN client and tap Add VPN Profile.
  8. Enter Your VPN Server IP (or DNS name) in the Server field.
    Note: If you specified the server's DNS name (instead of its IP address) during IKEv2 setup, you must enter the DNS name in the Server field.
  9. Select IKEv2 Certificate from the VPN Type drop-down menu.
  10. Tap Select user certificate, select the new client certificate and confirm.
  11. (Important) Tap Show advanced settings. Scroll down, find and enable the Use RSA/PSS signatures option.
  12. Save the new VPN connection, then tap to connect.

Android 4 to 9:

  1. Securely transfer the generated .p12 file to your Android device.
  2. Install strongSwan VPN Client from Google Play.
  3. Launch the strongSwan VPN client and tap Add VPN Profile.
  4. Enter Your VPN Server IP (or DNS name) in the Server field.
    Note: If you specified the server's DNS name (instead of its IP address) during IKEv2 setup, you must enter the DNS name in the Server field.
  5. Select IKEv2 Certificate from the VPN Type drop-down menu.
  6. Tap Select user certificate, then tap Install certificate.
  7. Choose the .p12 file you transferred from the VPN server, and follow the prompts.
    Note: To find the .p12 file, tap the three-line menu button, then browse to the location you saved the file.
  8. (Important) Tap Show advanced settings. Scroll down, find and enable the Use RSA/PSS signatures option.
  9. Save the new VPN connection, then tap to connect.

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".

If you get an error when trying to connect, see Troubleshooting.

Linux

Before configuring Linux VPN clients, you must make the following change on the VPN server: Edit /etc/ipsec.d/ikev2.conf on the server. Append authby=rsa-sha1 to the end of the conn ikev2-cp section, indented by two spaces. Save the file and run service ipsec restart.

To configure your Linux computer to connect to IKEv2 as a VPN client, first install the strongSwan plugin for NetworkManager:

# Ubuntu and Debian
sudo apt-get update
sudo apt-get install network-manager-strongswan

# Arch Linux
sudo pacman -Syu  # upgrade all packages
sudo pacman -S networkmanager-strongswan

# Fedora
sudo yum install NetworkManager-strongswan-gnome

# CentOS
sudo yum install epel-release
sudo yum --enablerepo=epel install NetworkManager-strongswan-gnome

Next, securely transfer the generated .p12 file from the VPN server to your Linux computer. After that, extract the CA certificate, client certificate and private key. Replace vpnclient.p12 in the example below with the name of your .p12 file.

# Example: Extract CA certificate, client certificate and private key.
#          You may delete the .p12 file when finished.
# Note: You will need to enter the import password, which can be found
#       in the output of the IKEv2 helper script.
openssl pkcs12 -in vpnclient.p12 -cacerts -nokeys -out ikev2vpnca.cer
openssl pkcs12 -in vpnclient.p12 -clcerts -nokeys -out vpnclient.cer
openssl pkcs12 -in vpnclient.p12 -nocerts -nodes  -out vpnclient.key
rm vpnclient.p12

# (Important) Protect certificate and private key files
# Note: This step is optional, but strongly recommended.
sudo chown root.root ikev2vpnca.cer vpnclient.cer vpnclient.key
sudo chmod 600 ikev2vpnca.cer vpnclient.cer vpnclient.key

You can then set up and enable the VPN connection:

  1. Go to Settings -> Network -> VPN. Click the + button.
  2. Select IPsec/IKEv2 (strongswan).
  3. Enter anything you like in the Name field.
  4. In the Gateway (Server) section, enter Your VPN Server IP (or DNS name) for the Address.
  5. Select the ikev2vpnca.cer file for the Certificate.
  6. In the Client section, select Certificate(/private key) in the Authentication drop-down menu.
  7. Select Certificate/private key in the Certificate drop-down menu (if exists).
  8. Select the vpnclient.cer file for the Certificate (file).
  9. Select the vpnclient.key file for the Private key.
  10. In the Options section, check the Request an inner IP address checkbox.
  11. In the Cipher proposals (Algorithms) section, check the Enable custom proposals checkbox.
  12. Leave the IKE field blank.
  13. Enter aes128gcm16 in the ESP field.
  14. Click Add to save the VPN connection information.
  15. Turn the VPN switch ON.

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".

If you get an error when trying to connect, see Troubleshooting.

Manage client certificates

List existing clients

If you want to list the names of existing IKEv2 clients, run the helper script with the --listclients option. Use option -h to show usage information.

Add a client certificate

To generate certificates for additional IKEv2 clients, just run the helper script again. Or you may refer to step 4 in this section.

Export configuration for an existing client

By default, the IKEv2 helper script exports client configuration after running. If later you want to export configuration for an existing client, run the helper script again and select the appropriate option.

Delete a client certificate

Important: Deleting a client certificate from the IPsec database WILL NOT prevent VPN client(s) from connecting using that certificate! For this use case, you MUST revoke the client certificate instead of deleting it.

First, read the important note above. Then click here for instructions.

Important: Please first read the important note above. If you still want to delete a certificate, refer to the steps below. This action cannot be undone!

To delete a client certificate:

  1. List certificates in the IPsec database:

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

    Example output:

    Certificate Nickname                               Trust Attributes
                                                       SSL,S/MIME,JAR/XPI
    
    IKEv2 VPN CA                                       CTu,u,u
    ($PUBLIC_IP)                                       u,u,u
    vpnclient                                          u,u,u
    
  2. Delete the client certificate and private key. Replace "Nickname" below with the nickname of the client certificate you want to delete, e.g. vpnclient.

    certutil -F -d sql:/etc/ipsec.d -n "Nickname"
    certutil -D -d sql:/etc/ipsec.d -n "Nickname" 2>/dev/null
  3. (Optional) Delete the previously generated client configuration files (.p12, .mobileconfig and .sswan files) for this VPN client, if any.

Revoke a client certificate

In certain circumstances, you may need to revoke a previously generated VPN client certificate. This can be done using crlutil. See example steps below, commands must be run as root.

  1. Check the database, and identify the nickname of the client certificate you want to revoke.

    certutil -L -d sql:/etc/ipsec.d
    Certificate Nickname                               Trust Attributes
                                                       SSL,S/MIME,JAR/XPI
    
    IKEv2 VPN CA                                       CTu,u,u
    ($PUBLIC_IP)                                       u,u,u
    vpnclient-to-revoke                                u,u,u
    

    In this example, we will revoke the certificate with nickname vpnclient-to-revoke, issued by IKEv2 VPN CA.

  2. Find the serial number of this client certificate.

    certutil -L -d sql:/etc/ipsec.d -n "vpnclient-to-revoke"
    Certificate:
        Data:
            Version: 3 (0x2)
            Serial Number:
                00:cd:69:ff:74
    ... ...
    

    From the output, we see that the serial number is CD69FF74 in hexadecimal, which is 3446275956 in decimal. It will be used in the next steps.

  3. Create a new Certificate Revocation List (CRL). You only need to do this once for each CA.

    if ! crlutil -L -d sql:/etc/ipsec.d -n "IKEv2 VPN CA" 2>/dev/null; then
      crlutil -G -d sql:/etc/ipsec.d -n "IKEv2 VPN CA" -c /dev/null
    fi
    CRL Info:
    :
        Version: 2 (0x1)
        Signature Algorithm: PKCS #1 SHA-256 With RSA Encryption
        Issuer: "O=IKEv2 VPN,CN=IKEv2 VPN CA"
        This Update: Sat Jun 06 22:00:00 2020
        CRL Extensions:
    
  4. Add the client certificate you want to revoke to the CRL. Here we specify the certificate's serial number in decimal, and the revocation time in GeneralizedTime format (YYYYMMDDhhmmssZ) in UTC.

    crlutil -M -d sql:/etc/ipsec.d -n "IKEv2 VPN CA" <<EOF
    addcert 3446275956 20200606220100Z
    EOF
    CRL Info:
    :
        Version: 2 (0x1)
        Signature Algorithm: PKCS #1 SHA-256 With RSA Encryption
        Issuer: "O=IKEv2 VPN,CN=IKEv2 VPN CA"
        This Update: Sat Jun 06 22:02:00 2020
        Entry 1 (0x1):
            Serial Number:
                00:cd:69:ff:74
            Revocation Date: Sat Jun 06 22:01:00 2020
        CRL Extensions:
    

    Note: If you want to remove a certificate from the CRL, replace addcert 3446275956 20200606220100Z above with rmcert 3446275956. For other crlutil usage, read here.

  5. Finally, let Libreswan re-read the updated CRL.

    ipsec crls

Manually set up IKEv2 on the VPN server

As an alternative to using the helper script, advanced users can manually set up IKEv2. Before continuing, it is recommended to update Libreswan to the latest version.

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

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

    PUBLIC_IP=$(dig @resolver1.opendns.com -t A -4 myip.opendns.com +short)
    [ -z "$PUBLIC_IP" ] && PUBLIC_IP=$(wget -t 3 -T 15 -qO- http://ipv4.icanhazip.com)
    printf '%s\n' "$PUBLIC_IP"

    Check to make sure the output matches the server's public IP. This variable is required in the steps below.

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

  2. Add a new IKEv2 connection:

    if ! grep -qs '^include /etc/ipsec\.d/\*\.conf$' /etc/ipsec.conf; then
      echo >> /etc/ipsec.conf
      echo 'include /etc/ipsec.d/*.conf' >> /etc/ipsec.conf
    fi

    Note: If you specified the server's DNS name (instead of its IP address) in step 1 above, you must replace leftid=$PUBLIC_IP in the command below with leftid=@$PUBLIC_IP.

    cat > /etc/ipsec.d/ikev2.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
      pfs=no
      fragmentation=yes
      ike=aes256-sha2,aes128-sha2,aes256-sha1,aes128-sha1,aes256-sha2;modp1024,aes128-sha1;modp1024
      phase2alg=aes_gcm-null,aes128-sha1,aes256-sha1,aes128-sha2,aes256-sha2
      ikelifetime=24h
      salifetime=24h
    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.d/ikev2.conf <<EOF
      modecfgdns="8.8.8.8 8.8.4.4"
      encapsulation=yes
      mobike=no
    EOF

    Note: The MOBIKE IKEv2 extension allows VPN clients to change network attachment points, e.g. switch between mobile data and Wi-Fi and keep the IPsec tunnel up on the new IP. If your server (or Docker host) is NOT running Ubuntu Linux, and you wish to enable MOBIKE support, replace mobike=no with mobike=yes in the command above. DO NOT enable this option on Ubuntu systems or Raspberry Pis.

    For Libreswan 3.19-3.22:

    cat >> /etc/ipsec.d/ikev2.conf <<EOF
      modecfgdns1=8.8.8.8
      modecfgdns2=8.8.4.4
      encapsulation=yes
    EOF

    For Libreswan 3.18 and older:

    cat >> /etc/ipsec.d/ikev2.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 120".

    Generate CA certificate:

    certutil -z <(head -c 1024 /dev/urandom) \
      -S -x -n "IKEv2 VPN CA" \
      -s "O=IKEv2 VPN,CN=IKEv2 VPN CA" \
      -k rsa -v 120 \
      -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
    

    Generate VPN server certificate:

    Note: If you specified the server's DNS name (instead of its IP address) in step 1 above, you must 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 -c "IKEv2 VPN CA" -n "$PUBLIC_IP" \
      -s "O=IKEv2 VPN,CN=$PUBLIC_IP" \
      -k rsa -v 120 \
      -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), then export the .p12 file that contains the client certificate, private key, and CA certificate.

    Note: You may repeat this step to generate certificates for additional VPN clients, but make sure to replace every vpnclient with vpnclient2, etc. To connect multiple VPN clients simultaneously, you must generate a unique certificate for each.

    Generate client certificate:

    certutil -z <(head -c 1024 /dev/urandom) \
      -S -c "IKEv2 VPN CA" -n "vpnclient" \
      -s "O=IKEv2 VPN,CN=vpnclient" \
      -k rsa -v 120 \
      -d sql:/etc/ipsec.d -t ",," \
      --keyUsage digitalSignature,keyEncipherment \
      --extKeyUsage serverAuth,clientAuth -8 "vpnclient"
    Generating key.  This may take a few moments...
    

    Export .p12 file:

    pk12util -d sql:/etc/ipsec.d -n "vpnclient" -o vpnclient.p12
    Enter password for PKCS12 file:
    Re-enter password:
    pk12util: PKCS12 EXPORT SUCCESSFUL
    

    Enter a secure password to protect the exported .p12 file (when importing into an iOS or macOS device, this password cannot be empty).

  5. (For iOS clients) Export the CA certificate as ikev2vpnca.cer:

    certutil -L -d sql:/etc/ipsec.d -n "IKEv2 VPN CA" -a -o ikev2vpnca.cer
  6. The database should now contain:

    certutil -L -d sql:/etc/ipsec.d
    Certificate Nickname                               Trust Attributes
                                                       SSL,S/MIME,JAR/XPI
    
    IKEv2 VPN 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 revoke a client certificate, follow these steps. For other certutil usage, read here.

  7. (Important) Restart the IPsec service:

    service ipsec restart

Before continuing, you must restart the IPsec service. The IKEv2 setup on the VPN server is now complete. Follow instructions to configure VPN clients.

Troubleshooting

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

Incorrect password when trying to import client config files

If you forgot the password for client config files, you may export configuration for the IKEv2 client again.

Ubuntu 18.04 users may encounter the error "The password you entered is incorrect" when trying to import the generated .p12 file into Windows. This is due to a bug in NSS. Read more here.

Workaround for the NSS bug on Ubuntu 18.04

Note: This workaround should only be used on Ubuntu 18.04 systems running on the x86_64 architecture. As of 2021-01-21, the IKEv2 helper script was updated to automatically apply this workaround.

First, install newer versions of libnss3 related packages:

wget https://mirrors.kernel.org/ubuntu/pool/main/n/nss/libnss3_3.49.1-1ubuntu1.5_amd64.deb
wget https://mirrors.kernel.org/ubuntu/pool/main/n/nss/libnss3-dev_3.49.1-1ubuntu1.5_amd64.deb
wget https://mirrors.kernel.org/ubuntu/pool/universe/n/nss/libnss3-tools_3.49.1-1ubuntu1.5_amd64.deb
apt-get -y update
apt-get -y install "./libnss3_3.49.1-1ubuntu1.5_amd64.deb" \
 "./libnss3-dev_3.49.1-1ubuntu1.5_amd64.deb" \
 "./libnss3-tools_3.49.1-1ubuntu1.5_amd64.deb"

After that, export configuration for the IKEv2 client again.

IKEv2 disconnects after one hour

If the IKEv2 connection disconnects automatically after one hour (60 minutes), apply this fix: Edit /etc/ipsec.d/ikev2.conf on the VPN server (or /etc/ipsec.conf if it does not exist), append these lines to the end of section conn ikev2-cp, indented by two spaces:

  ikelifetime=24h
  salifetime=24h

Save the file and run service ipsec restart. As of 2021-01-20, the IKEv2 helper script was updated to include this fix.

Unable to connect multiple IKEv2 clients

To connect multiple IKEv2 clients simultaneously, you must generate a unique certificate for each.

If you are unable to connect multiple IKEv2 clients simultaneously from behind the same NAT (e.g. home router), apply this fix: Edit /etc/ipsec.d/ikev2.conf on the VPN server, find the line leftid=@<your_server_ip> and remove the @, i.e. replace it with leftid=<your_server_ip>. Save the file and run service ipsec restart. Do not apply this fix if leftid is a DNS name, which is not affected. As of 2021-02-01, the IKEv2 helper script was updated to include this fix.

Other known issues

  1. The built-in VPN client in Windows may not support IKEv2 fragmentation (this feature requires Windows 10 v1803 or newer). 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 update Libreswan on your server to version 3.26 or above.

Additional troubleshooting

Click here for additional troubleshooting information.

Remove IKEv2

If you want to remove IKEv2 from the VPN server, but keep the IPsec/L2TP and IPsec/XAuth ("Cisco IPsec") modes (if installed), run the helper script again and select the "Remove IKEv2" option. Note that this will delete all IKEv2 configuration including certificates and keys, and cannot be undone!

Alternatively, you can manually remove IKEv2. Click here for instructions.

To manually remove IKEv2 from the VPN server, but keep the IPsec/L2TP and IPsec/XAuth ("Cisco IPsec") modes, follow these steps. Commands must be run as root. Note that this will delete all IKEv2 configuration including certificates and keys, and cannot be undone!

  1. Rename (or delete) the IKEv2 config file:

    mv /etc/ipsec.d/ikev2.conf /etc/ipsec.d/ikev2.conf.bak

    Note: If you used an older version (before 2020-05-31) of the IKEv2 helper script or instructions, file /etc/ipsec.d/ikev2.conf may not exist. In this case, please instead remove the conn ikev2-cp section from file /etc/ipsec.conf.

  2. (Important) Restart the IPsec service:

    service ipsec restart
  3. List certificates in the IPsec database:

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

    Example output:

    Certificate Nickname                               Trust Attributes
                                                       SSL,S/MIME,JAR/XPI
    
    IKEv2 VPN CA                                       CTu,u,u
    ($PUBLIC_IP)                                       u,u,u
    vpnclient                                          u,u,u
    
  4. Delete certificates and keys. Replace "Nickname" below with each certificate's nickname. Repeat these commands for each certificate. When finished, list certificates in the IPsec database again, and confirm that the list is empty.

    certutil -F -d sql:/etc/ipsec.d -n "Nickname"
    certutil -D -d sql:/etc/ipsec.d -n "Nickname" 2>/dev/null

References

License

Copyright (C) 2016-2021 Lin Song

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Attribution required: please include my name in any derivative and let me know how you have improved it!