Skip to content

Instantly share code, notes, and snippets.

@readloud

readloud/Configure_IPsec_L2TP_VPN_Clients.md

Created October 18, 2022 10:21
Show Gist options
  • Save readloud/eaceb86d99b36aa94be4dd403cc79b07 to your computer and use it in GitHub Desktop.
Save readloud/eaceb86d99b36aa94be4dd403cc79b07 to your computer and use it in GitHub Desktop.
Download ZIP
Configure_IPsec_L2TP_VPN_Clients
Raw
Configure_IPsec_L2TP_VPN_Clients.md

Configure IPsec/L2TP VPN Clients

IPsec/L2TP is natively supported by Android, iOS, OS X, and Windows. There is no additional software to install. Setup should only take a few minutes. In case you are unable to connect, first check to make sure the VPN credentials were entered correctly.

Windows

Windows 10 and 8.x

  1. Right-click on the wireless/network icon in your system tray.
  2. Select Open Network and Sharing Center. Or, if using Windows 10 version 1709 or newer, select Open Network & Internet settings, then on the page that opens, click Network and Sharing Center.
  3. Click Set up a new connection or network.
  4. Select Connect to a workplace and click Next.
  5. Click Use my Internet connection (VPN).
  6. Enter Your VPN Server IP in the Internet address field.
  7. Enter anything you like in the Destination name field, and then click Create.
  8. Return to Network and Sharing Center. On the left, click Change adapter settings.
  9. Right-click on the new VPN entry and choose Properties.
  10. Click the Security tab. Select "Layer 2 Tunneling Protocol with IPsec (L2TP/IPSec)" for the Type of VPN.
  11. Click Allow these protocols. Check the "Challenge Handshake Authentication Protocol (CHAP)" and "Microsoft CHAP Version 2 (MS-CHAP v2)" checkboxes.
  12. Click the Advanced settings button.
  13. Select Use preshared key for authentication and enter Your VPN IPsec PSK for the Key.
  14. Click OK to close the Advanced settings.
  15. Click OK to save the VPN connection details.

Note: A one-time registry change is required before connecting. See details below.

Alternatively, instead of following the steps above, you may create the VPN connection using these Windows PowerShell commands. Replace Your VPN Server IP and Your VPN IPsec PSK with your own values, enclosed in single quotes:

# Disable persistent command history
Set-PSReadlineOption –HistorySaveStyle SaveNothing
# Create VPN connection
Add-VpnConnection -Name 'My IPsec VPN' -ServerAddress 'Your VPN Server IP' -L2tpPsk 'Your VPN IPsec PSK' -TunnelType L2tp -EncryptionLevel Required -AuthenticationMethod Chap,MSChapv2 -Force -RememberCredential -PassThru
# Ignore the data encryption warning (data is encrypted in the IPsec tunnel)

Windows 7, Vista and XP

  1. Click on the Start Menu and go to the Control Panel.
  2. Go to the Network and Internet section.
  3. Click Network and Sharing Center.
  4. Click Set up a new connection or network.
  5. Select Connect to a workplace and click Next.
  6. Click Use my Internet connection (VPN).
  7. Enter Your VPN Server IP in the Internet address field.
  8. Enter anything you like in the Destination name field.
  9. Check the Don't connect now; just set it up so I can connect later checkbox.
  10. Click Next.
  11. Enter Your VPN Username in the User name field.
  12. Enter Your VPN Password in the Password field.
  13. Check the Remember this password checkbox.
  14. Click Create, and then Close.
  15. Return to Network and Sharing Center. On the left, click Change adapter settings.
  16. Right-click on the new VPN entry and choose Properties.
  17. Click the Options tab and uncheck Include Windows logon domain.
  18. Click the Security tab. Select "Layer 2 Tunneling Protocol with IPsec (L2TP/IPSec)" for the Type of VPN.
  19. Click Allow these protocols. Check the "Challenge Handshake Authentication Protocol (CHAP)" and "Microsoft CHAP Version 2 (MS-CHAP v2)" checkboxes.
  20. Click the Advanced settings button.
  21. Select Use preshared key for authentication and enter Your VPN IPsec PSK for the Key.
  22. Click OK to close the Advanced settings.
  23. Click OK to save the VPN connection details.

Note: This one-time registry change is required if the VPN server and/or client is behind NAT (e.g. home router).

To connect to the VPN: Click on the wireless/network icon in your system tray, select the new VPN entry, and click Connect. If prompted, enter Your VPN Username and Password, then click OK. 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

  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 L2TP over IPSec 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 for the Server Address.
  8. Enter Your VPN Username for the Account Name.
  9. Click the Authentication Settings button.
  10. In the User Authentication section, select the Password radio button and enter Your VPN Password.
  11. In the Machine Authentication section, select the Shared Secret radio button and enter Your VPN IPsec PSK.
  12. Click OK.
  13. Check the Show VPN status in menu bar checkbox.
  14. (Important) Click the Advanced button and make sure the Send all traffic over VPN connection checkbox is checked.
  15. Click the TCP/IP tab, and make sure Link-local only is selected in the Configure IPv6 section.
  16. Click OK to close the Advanced settings, and then click Apply to save the VPN connection information.

To connect to the VPN: Use the menu bar icon, or go to the Network section of System Preferences, select the VPN and choose Connect. 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. Launch the Settings application.
  2. Tap More... in the Wireless & Networks section.
  3. Tap VPN.
  4. Tap Add VPN Profile or the + icon at top-right of screen.
  5. Enter anything you like in the Name field.
  6. Select L2TP/IPSec PSK in the Type drop-down menu.
  7. Enter Your VPN Server IP in the Server address field.
  8. Enter Your VPN IPsec PSK in the IPSec pre-shared key field.
  9. Tap Save.
  10. Tap the new VPN connection.
  11. Enter Your VPN Username in the Username field.
  12. Enter Your VPN Password in the Password field.
  13. Check the Save account information checkbox.
  14. Tap Connect.

Once connected, you will see a VPN icon in the notification bar. 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

  1. Go to Settings -> General -> VPN.
  2. Tap Add VPN Configuration....
  3. Tap Type. Select L2TP and go back.
  4. Tap Description and enter anything you like.
  5. Tap Server and enter Your VPN Server IP.
  6. Tap Account and enter Your VPN Username.
  7. Tap Password and enter Your VPN Password.
  8. Tap Secret and enter Your VPN IPsec PSK.
  9. Make sure the Send All Traffic switch is ON.
  10. Tap Done.
  11. Slide the VPN switch ON.

Once connected, you will see a VPN icon in the status bar. 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.

Chromebook

  1. If you haven't already, sign in to your Chromebook.
  2. Click the status area, where your account picture appears.
  3. Click Settings.
  4. In the Internet connection section, click Add connection.
  5. Click Add OpenVPN / L2TP.
  6. Enter Your VPN Server IP for the Server hostname.
  7. Enter anything you like for the Service name.
  8. Make sure Provider type is L2TP/IPSec + pre-shared key.
  9. Enter Your VPN IPsec PSK for the Pre-shared key.
  10. Enter Your VPN Username for the Username.
  11. Enter Your VPN Password for the Password.
  12. Click Connect.

Once connected, you will see a VPN icon overlay on the network status icon. 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

Ubuntu Linux

Ubuntu 18.04 (and newer) users can install the network-manager-l2tp-gnome package, then configure the IPsec/L2TP VPN client using the GUI. Ubuntu 16.04 and 14.04 users may need to add the nm-l2tp PPA, read more here.

  1. Go to Settings -> Network -> VPN. Click the + button.
  2. Select Layer 2 Tunneling Protocol (L2TP).
  3. Enter anything you like in the Name field.
  4. Enter Your VPN Server IP for the Gateway.
  5. Enter Your VPN Username for the User name.
  6. Right-click the ? in the Password field, select Store the password only for this user.
  7. Enter Your VPN Password for the Password.
  8. Leave the NT Domain field blank.
  9. Click the IPsec Settings... button.
  10. Check the Enable IPsec tunnel to L2TP host checkbox.
  11. Leave the Gateway ID field blank.
  12. Enter Your VPN IPsec PSK for the Pre-shared key.
  13. Expand the Advanced section.
  14. Enter aes128-sha1-modp2048! for the Phase1 Algorithms.
  15. Enter aes128-sha1-modp2048! for the Phase2 Algorithms.
  16. Click OK, then click Add to save the VPN connection information.
  17. Turn the VPN switch ON.

Once 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".

Fedora and CentOS

Fedora 28 (and newer) and CentOS 7 users can connect using the faster IPsec/XAuth mode.

Other Linux

First check here to see if the network-manager-l2tp and network-manager-l2tp-gnome packages are available for your Linux distribution. If yes, install them (select strongSwan) and follow the instructions above. Alternatively, you may configure Linux VPN clients using the command line.

Troubleshooting

Windows Error 809

The network connection between your computer and the VPN server could not be established because the remote server is not responding.

To fix this error, a one-time registry change is required because the VPN server and/or client is behind NAT (e.g. home router). Download and import the .reg file below, or run the following from an elevated command prompt. You must reboot your PC when finished.

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

    REG ADD HKLM\SYSTEM\CurrentControlSet\Services\PolicyAgent /v AssumeUDPEncapsulationContextOnSendRule /t REG_DWORD /d 0x2 /f

  • For Windows XP ONLY (download .reg file)

    REG ADD HKLM\SYSTEM\CurrentControlSet\Services\IPSec /v AssumeUDPEncapsulationContextOnSendRule /t REG_DWORD /d 0x2 /f

Although uncommon, some Windows systems disable IPsec encryption, causing the connection to fail. To re-enable it, run the following command and reboot your PC.

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

    REG ADD HKLM\SYSTEM\CurrentControlSet\Services\RasMan\Parameters /v ProhibitIpSec /t REG_DWORD /d 0x0 /f

Windows Error 628

The connection was terminated by the remote computer before it could be completed.

To fix this error, please follow these steps:

  1. Right-click on the wireless/network icon in system tray, select Open Network and Sharing Center.
  2. On the left, click Change adapter settings. Right-click on the new VPN and choose Properties.
  3. Click the Security tab. Select "Layer 2 Tunneling Protocol with IPsec (L2TP/IPSec)" for Type of VPN.
  4. Click Allow these protocols. Make sure the "Challenge Handshake Authentication Protocol (CHAP)" checkbox is checked.
  5. Click the Advanced settings button.
  6. Select Use preshared key for authentication and enter Your VPN IPsec PSK for the Key.
  7. Click OK to close the Advanced settings.
  8. Click OK to save the VPN connection details.

Select CHAP in VPN connection properties

Windows 10 upgrades

After upgrading Windows 10 version (e.g. from 1709 to 1803), you may need to re-apply the fix above for Windows Error 809 and reboot.

Windows 8/10 DNS leaks

Windows 8.x and 10 use "smart multi-homed name resolution" by default, which may cause "DNS leaks" when using the native IPsec VPN client if your DNS servers on the Internet adapter are from the local network segment. To fix, you may either disable smart multi-homed name resolution, or configure your Internet adapter to use DNS servers outside your local network (e.g. 8.8.8.8 and 8.8.4.4). When finished, clear the DNS cache and reboot your PC.

In addition, if your computer has IPv6 enabled, all IPv6 traffic (including DNS queries) will bypass the VPN. Learn how to disable IPv6 in Windows.

macOS VPN traffic

OS X (macOS) users: If you can successfully connect using IPsec/L2TP mode, but your public IP does not show Your VPN Server IP, read the OS X section above and complete this step: Click the Advanced button and make sure the Send all traffic over VPN connection checkbox is checked. Then re-connect the VPN.

iOS/Android sleep mode

To save battery, iOS devices (iPhone/iPad) will automatically disconnect Wi-Fi shortly after the screen turns off (sleep mode). As a result, the IPsec VPN disconnects. This behavior is by design and cannot be configured. If you need the VPN to auto-reconnect when the device wakes up, try OpenVPN instead, which has support for options such as "Reconnect on Wakeup" and "Seamless Tunnel".

Android devices will also disconnect Wi-Fi shortly after entering sleep mode, unless the option "Keep Wi-Fi on during sleep" is enabled. This option is no longer available in Android 8 (Oreo). Alternatively, you may try enabling the "Always-on VPN" option to stay connected. Learn more here.

Android 6 and above

If you are unable to connect using Android 6 or above:

  1. Tap the "Settings" icon next to your VPN profile. Select "Show advanced options" and scroll down to the bottom. If the option "Backward compatible mode" exists (see image below), enable it and reconnect the VPN. If not, try the next step.
  2. Edit /etc/ipsec.conf on the VPN server. Find sha2-truncbug=yes and replace it with sha2-truncbug=no. Save the file and run service ipsec restart (Ref).

Android VPN workaround

Chromebook issues

Chromebook users: If you are unable to connect, try these steps: Edit /etc/ipsec.conf on the VPN server. Find the line phase2alg=... and append ,aes_gcm-null at the end. Save the file and run service ipsec restart.

Other errors

If you encounter other errors, refer to the links below:

Additional steps

Please try these additional troubleshooting steps:

First, restart services on the VPN server:

service ipsec restart
service xl2tpd restart

If using Docker, run docker restart ipsec-vpn-server.

Then reboot your VPN client device, and retry the connection. If still unable to connect, try removing and recreating the VPN connection, by following the instructions in this document. Make sure that the VPN credentials are entered correctly.

Check the Libreswan (IPsec) and xl2tpd logs for errors:

# Ubuntu & Debian
grep pluto /var/log/auth.log
grep xl2tpd /var/log/syslog

# CentOS & RHEL
grep pluto /var/log/secure
grep xl2tpd /var/log/messages

Check status of the IPsec VPN server:

ipsec status
ipsec verify

Show current established VPN connections:

ipsec whack --trafficstatus

Configure Linux VPN clients using the command line

Instructions below are based on the work of Peter Sanford. Commands must be run as root on your VPN client.

To set up the VPN client, first install the following packages:

# Ubuntu & Debian
apt-get update
apt-get -y install strongswan xl2tpd

# CentOS & RHEL
yum -y install epel-release
yum --enablerepo=epel -y install strongswan xl2tpd

# Fedora
yum -y install strongswan xl2tpd

Create VPN variables (replace with actual values):

VPN_SERVER_IP='your_vpn_server_ip'
VPN_IPSEC_PSK='your_ipsec_pre_shared_key'
VPN_USER='your_vpn_username'
VPN_PASSWORD='your_vpn_password'

Configure strongSwan:

cat > /etc/ipsec.conf <<EOF
# ipsec.conf - strongSwan IPsec configuration file

# basic configuration

config setup
  # strictcrlpolicy=yes
  # uniqueids = no

# Add connections here.

# Sample VPN connections

conn %default
  ikelifetime=60m
  keylife=20m
  rekeymargin=3m
  keyingtries=1
  keyexchange=ikev1
  authby=secret
  ike=aes128-sha1-modp2048!
  esp=aes128-sha1-modp2048!

conn myvpn
  keyexchange=ikev1
  left=%defaultroute
  auto=add
  authby=secret
  type=transport
  leftprotoport=17/1701
  rightprotoport=17/1701
  right=$VPN_SERVER_IP
EOF

cat > /etc/ipsec.secrets <<EOF
: PSK "$VPN_IPSEC_PSK"
EOF

chmod 600 /etc/ipsec.secrets

# For CentOS/RHEL & Fedora ONLY
mv /etc/strongswan/ipsec.conf /etc/strongswan/ipsec.conf.old 2>/dev/null
mv /etc/strongswan/ipsec.secrets /etc/strongswan/ipsec.secrets.old 2>/dev/null
ln -s /etc/ipsec.conf /etc/strongswan/ipsec.conf
ln -s /etc/ipsec.secrets /etc/strongswan/ipsec.secrets

Configure xl2tpd:

cat > /etc/xl2tpd/xl2tpd.conf <<EOF
[lac myvpn]
lns = $VPN_SERVER_IP
ppp debug = yes
pppoptfile = /etc/ppp/options.l2tpd.client
length bit = yes
EOF

cat > /etc/ppp/options.l2tpd.client <<EOF
ipcp-accept-local
ipcp-accept-remote
refuse-eap
require-chap
noccp
noauth
mtu 1280
mru 1280
noipdefault
defaultroute
usepeerdns
connect-delay 5000
name $VPN_USER
password $VPN_PASSWORD
EOF

chmod 600 /etc/ppp/options.l2tpd.client

The VPN client setup is now complete. Follow the steps below to connect.

Note: You must repeat all steps below every time you try to connect to the VPN.

Create xl2tpd control file:

mkdir -p /var/run/xl2tpd
touch /var/run/xl2tpd/l2tp-control

Restart services:

service strongswan restart
service xl2tpd restart

Start the IPsec connection:

# Ubuntu & Debian
ipsec up myvpn

# CentOS/RHEL & Fedora
strongswan up myvpn

Start the L2TP connection:

echo "c myvpn" > /var/run/xl2tpd/l2tp-control

Run ifconfig and check the output. You should now see a new interface ppp0.

Check your existing default route:

ip route

Find this line in the output: default via X.X.X.X .... Write down this gateway IP for use in the two commands below.

Exclude your VPN server's IP from the new default route (replace with actual value):

route add YOUR_VPN_SERVER_IP gw X.X.X.X

If your VPN client is a remote server, you must also exclude your Local PC's public IP from the new default route, to prevent your SSH session from being disconnected (replace with actual value):

route add YOUR_LOCAL_PC_PUBLIC_IP gw X.X.X.X

Add a new default route to start routing traffic via the VPN server：

route add default dev ppp0

The VPN connection is now complete. Verify that your traffic is being routed properly:

wget -qO- http://ipv4.icanhazip.com; echo

The above command should return Your VPN Server IP.

To stop routing traffic via the VPN server:

route del default dev ppp0

To disconnect:

# Ubuntu & Debian
echo "d myvpn" > /var/run/xl2tpd/l2tp-control
ipsec down myvpn

# CentOS/RHEL & Fedora
echo "d myvpn" > /var/run/xl2tpd/l2tp-control
strongswan down myvpn
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment