IKEv2-setup

Table of contents

• What?
  • VPN server
  • VPN clients
  • Caveats
• How?
  • Troubleshooting
  • Users
  • Upgrades
  • Bonus paranoia
• Why?
  • Why IKEv2?
  • Why not Algo?

What?

A Bash script that takes Ubuntu Server 22.04, 20.04 or 18.04 LTS from clean install to production-ready IKEv2 VPN with strongSwan. Comments and pull requests welcome. It may still work on older Ubuntu versions back to 16.10 if you remove the version check, but these are not tested.

VPN server

• The VPN server identifies itself with a Let's Encrypt certificate, so there's no need for clients to install private certificates — they can simply authenticate with username and strong password (EAP-MSCHAPv2).

• The preferred cipher set is the US Commercial National Security Algorithm Suite (CNSA): aes256gcm16-prfsha384-ecp384. However, due to an apparent bug in recent versions of macOS, aes256gcm16-prfsha256-ecp256 is also accepted.

• The box is firewalled with iptables and configured for unattended security upgrades, and the Let's Encrypt certificate is set up to auto-renew, so it could be safe to forget about it all until your chosen Ubuntu version reaches end-of-life. (Note that iptables setup includes basic rate-limiting, dropping new connections if there have been 60+ connection attempts in the last 5 minutes).

VPN clients

The VPN is tested working with:

• macOS 10.12 – 14, iOS 10 – 17 — Built-in clients. A .mobileconfig profile is generated for iOS, to set up secure ciphers and enable Connect on demand support. An AppleScript script is generated for Mac, to prompt for VPN credentials and then do the same.
• Windows 10 Pro, 11 Pro — Built-in client. PowerShell commands are generated to configure the VPN and secure ciphers.
• Ubuntu (17.04 and presumably others) — Using strongSwan. A Bash script is generated to set this up.
• Android — Using the official strongSwan app. A .sswan file is generated for configuration.

Configuration files, scripts and instructions are sent by email. They are also dropped in the newly-created non-root user's home directory on the server (this point may be important, because VPS providers sometimes block traffic on port 25 by default and, even if successfully sent, conscientious email hosts will sometimes mark the email as spam).

Caveats

• There's no IPv6 support — and, in fact, IPv6 networking is disabled — because supporting IPv6 prevents the use of forceencaps, and honestly also because I haven't got to grips with the security implications (ip6tables rules and so on).
• The script won't work as-is on 16.04 LTS or earlier (where the certbot package is outdated, found under the name letsencrypt, and doesn't renew certificates automatically).
• Don't use this unmodified on a server you use for anything else: it does as it sees fit with various wider settings that may conflict with what you're doing.

How?

1. Pick a domain name for the VPN server and ensure that it already resolves to the correct IP by creating the appropriate A record in the DNS and making sure it has propagated. Let's Encrypt needs this in order to create your server certificate.

Don't want to use your own domain name here? You could try using the reverse DNS name provided by your server host, or an automatic IP/DNS alias service such as sslip.io, xip.io, nip.io, s.test.cab, or xip.lhjmmc.cn (earlier versions of this script used an sslip.io address by default). However, these options may fall foul of Let's Encrypt's per-domain rate limit of 50 certificates per week. Note that ephemeral AWS domain names like ec2-34-267-212-76.compute-1.amazonaws.com are not accepted by Let's Encrypt.

2. Start with a clean Ubuntu Server installation. The cheapest VPSs offered by Linode, OVH, vps.ag, Google, AWS Lightsail, Hetzner and Vultr, and Scaleway's ARM64-2GB, have all been tested working. On Scaleway, unblock SMTP ports in the admin panel and hard reboot the server first, or your configuration email will not be delivered. On Vultr, port 25 may also be blocked, but you won't know, and the only way to fix it is to open a support ticket.

3. Optionally, set up key-based SSH authentication (alternatively, this may have been handled automatically by your server provider, or you may choose to stick with password-based authentication). This may require you to run some or all of the following commands, with appropriate substitutions, on the machine you're going to be logging in from:

   ssh-keygen -t ed25519 -C "[email protected]"      # if you need a new key, ed25519 is the latest and possibly most secure option
   ssh-keygen -t rsa -b 4096 -C "[email protected]"  # alternatively, use RSA and go (4,096 bits) large
   
   ssh [email protected]  # if your host forces a password change before anything else (e.g. Hetzner), do it now, then exit
   ssh-copy-id -i ~/.ssh/id_ed25519.pub [email protected]  # copy your public key over to the VPN server
   ssh [email protected]  # log back in to the server for the next step ...
   

4. On your new server installation, become root, download the script, give it execute permissions, and run it:

   wget https://raw.githubusercontent.com/jawj/IKEv2-setup/master/setup.sh
   chmod u+x setup.sh
   ./setup.sh
   

5. You'll be prompted to enter all the necessary details after the software updates and installations complete. If you are not using key-based SSH authentication, you must pick a really strong password for the login user when prompted, or your server will be compromised.

   The part of your session where the script asks you questions should look something like this:

    --- Configuration: VPN settings ---
   
    Network interface: eth0
    External IP: 100.100.100.100
   
    ** Note: hostname must resolve to this machine already, to enable Let's Encrypt certificate setup **
    Hostname for VPN: 
    VPN username: george
    VPN password (no quotes, please): 
    Confirm VPN password: 
   
    Public DNS servers include:
   
    176.103.130.130,176.103.130.131  AdGuard               https://adguard.com/en/adguard-dns/overview.html
    176.103.130.132,176.103.130.134  AdGuard Family        https://adguard.com/en/adguard-dns/overview.html
    1.1.1.1,1.0.0.1                  Cloudflare/APNIC      https://1.1.1.1
    84.200.69.80,84.200.70.40        DNS.WATCH             https://dns.watch
    8.8.8.8,8.8.4.4                  Google                https://developers.google.com/speed/public-dns/
    208.67.222.222,208.67.220.220    OpenDNS               https://www.opendns.com
    208.67.222.123,208.67.220.123    OpenDNS FamilyShield  https://www.opendns.com
    9.9.9.9,149.112.112.112          Quad9                 https://quad9.net
    77.88.8.8,77.88.8.1              Yandex                https://dns.yandex.com
    77.88.8.88,77.88.8.2             Yandex Safe           https://dns.yandex.com
    77.88.8.7,77.88.8.3              Yandex Family         https://dns.yandex.com
   
    DNS servers for VPN users (default: 1.1.1.1,1.0.0.1): 176.103.130.130,176.103.130.131
   
    --- Configuration: general server settings ---
   
    Timezone (default: Europe/London): 
    Email address for sysadmin (e.g. [email protected]): [email protected]
    Desired SSH log-in port (default: 22): 2222
    New SSH log-in user name: george
    Copy /root/.ssh/authorized_keys to new user and disable SSH password log-in [Y/n]? y
    New SSH user's password (e.g. for sudo): 
    Confirm new SSH user's password: 
   

6. Once you're up and running, use these commands for some insight into what's going on:

    sudo ipsec statusall           # status, who's connected, etc.
    sudo iptables -L -v            # how much traffic has been forwarded, dropped, etc.?
    sudo tail -f /var/log/syslog   # real-time logs of (dis)connections etc.
   

Troubleshooting

If you ran this script before 13 September 2021, and used the generated PowerShell commands to set up Windows 10 clients, those clients may be unable to connect owing to a bug in Windows 10. If this is the case, see issue #126.

Otherwise, if things don't work out right away ...

• On the client: make sure you created the connection using the newly emailed .mobileconfig file, AppleScript or PowerShell commands. Setting it up manually via the OS GUI will not work, since it will default to insecure ciphers which the server has not been configured to support. Also note that .mobileconfig files generated with earlier iterations of this script may no longer be compatible, since the configured ciphers have changed from time to time.

• On the server: check that network ingress for UDP on ports 500 and 4500 is enabled (on some cloud platforms you'll have to add appropriate firewall rules to your virtual network). Also check that packet forwarding is enabled (on some cloud platforms this is controlled by a configuration setting that's off by default).

• Check the server logs on strongSwan startup and when you try to connect, and the client logs when you try to connect.

  • On the server: Log in via SSH, then sudo tail -f /var/log/syslog. To see startup logs, log in to another session and sudo ipsec restart there, then switch back. To see what's logged during a connection attempt, try to connect from a client.

  • On the client: On a Mac, open Console.app in /Applications/Utilities. If connecting from an iPhone, plug the iPhone into the Mac. Pick the relevant device (in the bar down the left), filter the output (in the box at top right) to nesession, and try to connect. (On Windows or Linux I don't know where you find the logs — if you know, feel free to write the explanation and send a pull request).

• The setup script is now more or less idempotent — you should be able to run it repeatedly with no ill effects — so, when you've fixed any issues, simply run it again.

• If you have a tricky question about strongSwan, it's probably better to raise it with the strongSwan team than file an issue here.

Users

To add or change VPN users, it's:

  sudo nano /etc/ipsec.secrets

Edit usernames and passwords as you see fit (but don't touch the first line, which specifies the server certificate). The line format for each user is:

  someusername : EAP "somepassword"

To exit nano it's Ctrl + O then Ctrl + X, and to have strongSwan pick up the changes it's:

  sudo ipsec secrets

Upgrades

If you're on an older version of Ubuntu, it's probably easiest to make a record of any changes to ipsec.secrets, blow the whole thing away and reinstall, then reinstate ipsec.secrets.

Note that you may also need to delete and recreate all your client connection settings using the updated PowerShell commands or .mobileconfig file, since there have been a few cipher changes over time.

Bonus paranoia

Your traffic is not logged on the server, but if you're feeling especially paranoid there are various things you could do to reduce logging further. A simple and somewhat drastic option (once you've got everything working) is:

  sudo rm /var/log/syslog && sudo ln -s /dev/null /var/log/syslog
  sudo rm /var/log/auth.log && sudo ln -s /dev/null /var/log/auth.log

Why?

We use a similar setup as a corporate VPN at PSYT. And I use this to bounce my personal web browsing via Europe, in the hope of giving Theresa May's Investigatory Powers Bill the finger.

Why IKEv2?

• Fair security
• Built-in clients for latest iOS, Mac and Windows (+ trustworthy free install on Android)
• Connect on demand support on iOS and Mac
• Robust to connection switching and interruptions via MOBIKE

More on IKEv2 at https://www.cl.cam.ac.uk/~mas90/resources/strongswan/ and https://www.bestvpn.com/blog/4147/pptp-vs-l2tp-vs-openvpn-vs-sstp-vs-ikev2/

Why not Algo?

Feel free to use Algo instead. It has similar aims, and now configures WireGuard too. However, it has many more moving parts, and requires several local installation steps before you even start setting up your VPN. This script is intended to be much simpler.