# Step-by-Step Guide: How to Set Up IKEv2 VPN

*Read this in other languages: [English](ikev2-howto.md), [简体中文](ikev2-howto-zh.md).*

**Important:** This guide is for **advanced users** only. Other users please use [IPsec/L2TP](clients.md) or [IPsec/XAuth](clients-xauth.md) mode.

---
* [Introduction](#introduction)
* [Set up IKEv2 on the VPN server](#set-up-ikev2-on-the-vpn-server)
* [Configure IKEv2 VPN clients](#configure-ikev2-vpn-clients)
* [Known issues](#known-issues)
* [References](#references)

## 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 <a href="https://en.wikipedia.org/wiki/Internet_Key_Exchange#Improvements_with_IKEv2" target="_blank">improvements</a> 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)
- Android 4.x and newer (using the strongSwan VPN client)
- iOS (iPhone/iPad)

## Set up IKEv2 on the VPN server

**Important:** As a prerequisite to using this guide, and before continuing, you must make sure that you have successfully <a href="https://github.com/hwdsl2/setup-ipsec-vpn" target="_blank">set up your own VPN server</a>, and (optional but recommended) <a href="../README.md#upgrade-libreswan" target="_blank">upgraded Libreswan</a> to the latest version.

The following example shows how to 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.

   ```bash
   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`.

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

   ```bash
   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
     pfs=no
     ike-frag=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
   EOF
   ```

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

   ```bash
   ipsec --version
   ```

   For Libreswan 3.23 and newer:

   ```bash
   cat >> /etc/ipsec.conf <<EOF
     modecfgdns="8.8.8.8 8.8.4.4"
     encapsulation=yes
     mobike=no
   EOF
   ```

   **Note:** If your server runs Debian or CentOS/RHEL 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.

   For Libreswan 3.19-3.22:

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

   For Libreswan 3.18 and older:

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

1. 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:

   ```bash
   certutil -z <(head -c 1024 /dev/urandom) \
     -S -x -n "IKEv2 VPN CA" \
     -s "O=IKEv2 VPN,CN=IKEv2 VPN CA" \
     -k rsa -g 4096 -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"`.

   ```bash
   certutil -z <(head -c 1024 /dev/urandom) \
     -S -c "IKEv2 VPN CA" -n "$PUBLIC_IP" \
     -s "O=IKEv2 VPN,CN=$PUBLIC_IP" \
     -k rsa -g 4096 -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...
   ```

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

   Generate client certificate:

   ```bash
   certutil -z <(head -c 1024 /dev/urandom) \
     -S -c "IKEv2 VPN CA" -n "vpnclient" \
     -s "O=IKEv2 VPN,CN=vpnclient" \
     -k rsa -g 4096 -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:

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

   ```
   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). You may repeat this step to generate certificates for additional VPN clients, but make sure to replace every `vpnclient` with `vpnclient2`, etc.

   **Note:** To connect multiple VPN clients simultaneously, you must generate a unique certificate for each.

1. (For iOS clients) Export the CA certificate as `vpnca.cer`:

   ```bash
   certutil -L -d sql:/etc/ipsec.d -n "IKEv2 VPN CA" -a -o vpnca.cer
   ```

1. The database should now contain:

   ```bash
   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 delete a certificate, replace `-L` with `-D`. For other `certutil` usage, read <a href="http://manpages.ubuntu.com/manpages/xenial/en/man1/certutil.1.html" target="_blank">this page</a>.

1. **(Important) Restart the IPsec service**:

   ```bash
   service ipsec restart
   ```

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

## Configure IKEv2 VPN clients

**Note:** If you specified the server's DNS name (instead of its IP address) in step 1 above, you must enter the DNS name in the **Server** and **Remote ID** fields.

* [Windows 7, 8.x and 10](#windows-7-8x-and-10)
* [OS X (macOS)](#os-x-macos)
* [Android 10 and newer](#android-10-and-newer)
* [Android 4.x to 9.x](#android-4x-to-9x)
* [iOS (iPhone/iPad)](#ios)

### Windows 7, 8.x and 10

1. Securely transfer `vpnclient.p12` to your computer, then import it into 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

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

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

1. (Optional) Enable stronger ciphers by adding the registry key `NegotiateDH2048_AES256` and reboot. Read more <a href="https://wiki.strongswan.org/projects/strongswan/wiki/WindowsClients#AES-256-CBC-and-MODP2048" target="_blank">here</a>.

### OS X (macOS)

First, securely transfer `vpnclient.p12` 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. When finished, check to make sure both `vpnclient` and `IKEv2 VPN CA` are listed under the **Certificates** category of **login** keychain.

1. Open System Preferences and go to the Network section.
1. Click the **+** button in the lower-left corner of the window.
1. Select **VPN** from the **Interface** drop-down menu.
1. Select **IKEv2** from the **VPN Type** drop-down menu.
1. Enter anything you like for the **Service Name**.
1. Click **Create**.
1. Enter `Your VPN Server IP` (or DNS name) for the **Server Address**.
1. Enter `Your VPN Server IP` (or DNS name) for the **Remote ID**.
1. Leave the **Local ID** field blank.
1. Click the **Authentication Settings...** button.
1. Select **None** from the **Authentication Settings** drop-down menu.
1. Select the **Certificate** radio button, then select the **vpnclient** certificate.
1. Click **OK**.
1. Check the **Show VPN status in menu bar** checkbox.
1. Click **Apply** to save the VPN connection information.
1. Click **Connect**.

### Android 10 and newer

1. Securely transfer `vpnclient.p12` to your Android device.
1. Install <a href="https://play.google.com/store/apps/details?id=org.strongswan.android" target="_blank">strongSwan VPN Client</a> from **Google Play**.
1. Launch the **Settings** application.
1. Go to Security -> Advanced -> Encryption & credentials.
1. Tap **Install from storage (or SD card)**.
1. Choose the `.p12` file you copied from the VPN server, and follow the prompts.   
   **Note:** To find the `.p12` file, click on the three-line menu button, then click on your device name.
1. Launch the strongSwan VPN client and tap **Add VPN Profile**.
1. Enter `Your VPN Server IP` (or DNS name) in the **Server** field.
1. Select **IKEv2 Certificate** from the **VPN Type** drop-down menu.
1. Tap **Select user certificate**, select your new VPN client certificate and confirm.
1. **(Important)** Tap **Show advanced settings**. Scroll down, find and enable the **Use RSA/PSS signatures** option.
1. Save the new VPN connection, then tap to connect.

### Android 4.x to 9.x

1. Securely transfer `vpnclient.p12` to your Android device.
1. Install <a href="https://play.google.com/store/apps/details?id=org.strongswan.android" target="_blank">strongSwan VPN Client</a> from **Google Play**.
1. Launch the strongSwan VPN client and tap **Add VPN Profile**.
1. Enter `Your VPN Server IP` (or DNS name) in the **Server** field.
1. Select **IKEv2 Certificate** from the **VPN Type** drop-down menu.
1. Tap **Select user certificate**, then tap **Install certificate**.
1. Choose the `.p12` file you copied from the VPN server, and follow the prompts.   
   **Note:** To find the `.p12` file, click on the three-line menu button, then click on your device name.
1. **(Important)** Tap **Show advanced settings**. Scroll down, find and enable the **Use RSA/PSS signatures** option.
1. Save the new VPN connection, then tap to connect.

### iOS

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

1. AirDrop, or
1. Upload the files to your device, tap them in the "Files" app, then go to "Settings" and import, or
1. Host the files on a secure website of yours, then download and import them in Mobile Safari.

When finished, check to make sure both `vpnclient` and `IKEv2 VPN CA` are listed under Settings -> General -> Profiles.

1. Go to Settings -> General -> VPN.
1. Tap **Add VPN Configuration...**.
1. Tap **Type**. Select **IKEv2** and go back.
1. Tap **Description** and enter anything you like.
1. Tap **Server** and enter `Your VPN Server IP` (or DNS name).
1. Tap **Remote ID** and enter `Your VPN Server IP` (or DNS name).
1. Leave the **Local ID** field blank.
1. Tap **User Authentication**. Select **None** and go back.
1. Make sure the **Use Certificate** switch is ON.
1. Tap **Certificate**. Select **vpnclient** and go back.
1. Tap **Done**.
1. Slide the **VPN** switch ON.

Once successfully connected, you can verify that your traffic is being routed properly by <a href="https://www.google.com/search?q=my+ip" target="_blank">looking up your IP address on Google</a>. 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 <a href="clients.md" target="_blank">IPsec/L2TP</a> or <a href="clients-xauth.md" target="_blank">IPsec/XAuth</a> mode.
1. If using the strongSwan Android VPN client, you must <a href="../README.md#upgrade-libreswan" target="_blank">upgrade Libreswan</a> on your server to version 3.26 or above.
1. If your VPN client can connect but cannot open any website, try editing `/etc/ipsec.conf` on the VPN server. Find the line `phase2alg=` under section `conn ikev2-cp` and delete `aes_gcm-null,`. Save the file and run `service ipsec restart`.
1. Ubuntu 18.04 and CentOS 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 <a href="https://github.com/hwdsl2/setup-ipsec-vpn/issues/414#issuecomment-460430354" target="_blank">here</a>.
1. Connecting multiple IKEv2 clients simultaneously from behind the same NAT (e.g. home router) is not supported at this time. For this use case, please instead use <a href="clients-xauth.md" target="_blank">IPsec/XAuth</a> mode.

## 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