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Title       : 	IPSEC L2TP VPN on Arch Linux on a Raspberry Pi with OpenSwan, xl2tpd and ppp
Author      : 	Remy van Elst
Date        : 	01-12-2014
URL         : 	https://raymii.org/s/tutorials/IPSEC_L2TP_vpn_on_a_Raspberry_Pi_with_Arch_Linux.html
Format      : 	Markdown/HTML
The Raspberry Pi is a great little small computer, both for tinkering but also
as a low power 24/7 running homeserver system. I've got multiple Pi's, one
running as my home VPN gateway. It is running an IPSEC/L2TP VPN server. This is
a guide on setting up an IPSEC/L2TP vpn server with Arch Linux on the Raspberry
Pi using Openswan as the IPsec server, xl2tpd as the l2tp provider and ppp or
local users / PAM for authentication. It has a detailed explanation with every
step. We choose the IPSEC/L2TP protocol stack because of recent vulnerabilities
found in pptpd VPNs.
This tutorial is available for the following platforms:
  * [Raspberry Pi with Arch Linux ARM][2]
  * [CentOS 7, Scientific Linux 7 or Red Hat Enterprise Linux 7 (IKEv2,no L2TP)][3]
  * [CentOS 6, Scientific Linux 6 or Red Hat Enterprise Linux 6][4]
  * [Ubuntu 16.04, (IKEv2,no L2TP)][5]
  * [Ubuntu 15.10, (IKEv2,no L2TP)][6]
  * [Ubuntu 15.04, (IKEv2,no L2TP)][7]
  * [Ubuntu 14.04 LTS][8]
  * [Ubuntu 13.10][9]
  * [Ubuntu 13.04][10]
  * [Ubuntu 12.10][11]
  * [Ubuntu 12.04 LTS][12]

I'm developing an open source monitoring app called Leaf Node Monitoring, for windows, linux & android. Go check it out!

Consider sponsoring me on Github. It means the world to me if you show your appreciation and you'll help pay the server costs.

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This tutorial was tested on a Raspberry Pi running Arch Linux ARM, installed via
NOOBS. It ran the current up to date Arch Linux ARM, here are the versions used:
  * `uname -a`: Linux pi2.raymii.nl 3.10.25-1-ARCH #1 PREEMPT Mon Dec 23 16:07:25 MST 2013 armv6l GNU/Linux
  * `ipsec --version`: Linux Openswan U2.6.39/K3.10.25-1-ARCH (netkey)
  * `xl2tpd -v`: xl2tpd version: xl2tpd-1.3.1
  * `pppd --version`: pppd version 2.4.5
IPSec encrypts your IP packets to provide encryption and authentication, so no
one can decrypt or forge data between your clients and your server. L2TP
provides a tunnel to send data. It does not provide encryption and
authentication though, that is why we combine the two.
To work trough this tutorial you should have:
  * 1 Raspberry Pi running Arch Linux ARM
  * 1 (or more) clients running an OS that support IPsec/L2tp vpns (Ubuntu, Mac OS, Windows, Android).
  * Ports 1701 TCP, 4500 UDP and 500 UDP opened in the firewall.
I do all the steps as the root user. You should do to, but only via `sudo -i` or
`su -`. Do not allow root to login via SSH!
#### Install ppp openswan and xl2tpd
First we will install the required packages:
    pacman -Sy openswan xl2tpd ppp lsof python2
If you are running normal Arch (x86), you need to install OpenSWAN from the AUR.
For the ARM/Pi version there is a package available. Python2 is required for
OpenSWAN, but not listed as a dependency, therefore it is installed.
#### Firewall and sysctl
We are going to set the firewall and make sure the kernel forwards IP packets:
Execute this command to enable the iptables firewall to allow vpn traffic:
    iptables --table nat --append POSTROUTING --jump MASQUERADE
Execute the below commands to enable kernel IP packet forwarding and disable ICP
    echo "net.ipv4.ip_forward = 1" |  tee -a /etc/sysctl.conf
    echo "net.ipv4.conf.all.accept_redirects = 0" |  tee -a /etc/sysctl.conf
    echo "net.ipv4.conf.all.send_redirects = 0" |  tee -a /etc/sysctl.conf
    echo "net.ipv4.conf.default.rp_filter = 0" |  tee -a /etc/sysctl.conf
    echo "net.ipv4.conf.default.accept_source_route = 0" |  tee -a /etc/sysctl.conf
    echo "net.ipv4.conf.default.send_redirects = 0" |  tee -a /etc/sysctl.conf
    echo "net.ipv4.icmp_ignore_bogus_error_responses = 1" |  tee -a /etc/sysctl.conf
Set these settings for other network interfaces:
    for vpn in /proc/sys/net/ipv4/conf/*; do echo 0 > $vpn/accept_redirects; echo 0 > $vpn/send_redirects; done
Apply them:
    sysctl -p
##### Persistent settings via systemd
Arch Linux uses systemd. Init script functionality like rc.local is not
available. To have these settings applied at boot we can however create a custom
systemd service which starts at boot.
Add the following code to `/usr/local/bin/vpn-boot.sh`:
    #!/usr/bin/env bash
    for vpn in /proc/sys/net/ipv4/conf/*; do 
        echo 0 > $vpn/accept_redirects; 
        echo 0 > $vpn/send_redirects; 
    iptables --table nat --append POSTROUTING --jump MASQUERADE
    sysctl -p
Make it executable:
    chmod 755 /usr/local/bin/vpn-boot.sh
Using the following systemd service we can start the script which sets the above
things at boot:
Add the following code to `/etc/systemd/system/vpnboot.service`:
    Description=VPN Settings at boot
    Before=openswan.service xl2tpd.service
Then enable it:
    systemctl enable vpnboot.service
#### Configure Openswan (IPSEC)
Use your favorite editor to edit the following file:
    vim /etc/ipsec.conf  
Replace the contents with the following:
(Most lines have a comment below it explaining what it does.)
    version 2 
    config setup
        #in what directory should things started by setup (notably the Pluto daemon) be allowed to dump core?
        #whether to accept/offer to support NAT (NAPT, also known as "IP Masqurade") workaround for IPsec
        #contains the networks that are allowed as subnet= for the remote client. In other words, the address ranges that may live behind a NAT router through which a client connects.
        #decide which protocol stack is going to be used.
        # replace with your ethernet interface.
        # Send a keep-alive packet every 60 seconds.
    conn L2TP-PSK-noNAT
        #shared secret. Use rsasig for certificates.
        #Enable pfs
        #the ipsec tunnel should be started and routes created when the ipsec daemon itself starts.
        #Only negotiate a conn. 3 times.
        #because we use l2tp as tunnel protocol
        #fill in server IP above
        # Dead Peer Dectection (RFC 3706) keepalives delay
        #  length of time (in seconds) we will idle without hearing either an R_U_THERE poll from our peer, or an R_U_THERE_ACK reply.
        # When a DPD enabled peer is declared dead, what action should be taken. clear means the eroute and SA with both be cleared.
Replace %SERVERIP% with the external IP of your Raspberry Pi. You can find it
out by:
    curl http://ip.mtak.nl
##### The shared secret
The shared secret is defined in the `/etc/ipsec.secrets` file. Make sure it is
long and random:
    %SERVERIP%  %any:   PSK "Your secret random key"
Again, replace %SERVERIP% with the external IP of your Raspberry Pi. If you want
to generate a random key you can use the following openssl command:
    openssl rand -hex 30
Example output:
##### Verify IPSEC Settings
Now to make sure IPSEC works, execute the following command:
    ipsec verify
My output looks like this:
     Checking if IPsec got installed and started correctly:
    Version check and ipsec on-path                     [OK]
    Openswan U2.6.39/K3.10.25-1-ARCH (netkey)
    See `ipsec --copyright' for copyright information.
    Checking for IPsec support in kernel                [OK]
     NETKEY: Testing XFRM related proc values
             ICMP default/send_redirects                [OK]
             ICMP default/accept_redirects              [OK]
             XFRM larval drop                           [OK]
    Hardware random device check                        [N/A]
    Two or more interfaces found, checking IP forwarding    [OK]
    Checking rp_filter                                  [ENABLED]
     /proc/sys/net/ipv4/conf/default/rp_filter          [ENABLED]
     /proc/sys/net/ipv4/conf/eth0/rp_filter             [ENABLED]
     /proc/sys/net/ipv4/conf/ifb0/rp_filter             [ENABLED]
     /proc/sys/net/ipv4/conf/ifb1/rp_filter             [ENABLED]
    Checking that pluto is running                      [OK]
     Pluto listening for IKE on udp 500               fail in else:State      Recv-Q Send-Q        Local Address:Port          Peer Address:Port
     Pluto listening for IKE on tcp 500                 [NOT IMPLEMENTED]
     Pluto listening for IKE/NAT-T on udp 4500          [DISABLED]
     Pluto listening for IKE/NAT-T on tcp 4500          [NOT IMPLEMENTED]
     Pluto listening for IKE on tcp 10000 (cisco)       [NOT IMPLEMENTED]
    Checking NAT and MASQUERADEing                      [TEST INCOMPLETE]
    Checking 'ip' command                               [OK]
    Checking 'iptables' command                         [OK]
    ipsec verify: encountered errors
However, a `netstat -tulpan` shows that `pluto` is listening on the ports that
give errors:
    Active Internet connections (servers and established)
    Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
    udp        0      0*                           4624/pluto
    udp        0      0  *                           4443/xl2tpd
    udp        0      0 *                           4624/pluto
Enable Openswan:
    systemctl enable openswan
#### Configure xl2tpd
Use your favorite editor to edit the following file:
Replace the contents with the following:
    ipsec saref = yes
    saref refinfo = 30
    [lns default]
    ip range =
    local ip =
    refuse pap = yes
    require authentication = yes
    ppp debug = yes
    pppoptfile = /etc/ppp/options.xl2tpd
    length bit = yes
  * ip range = range of IPs to give to the connecting clients
  * local ip = IP of VPN server
  * refuse pap = refure pap authentication
  * ppp debug = yes when testing, no when in production
Also create the following folder for xl2tpd's control file:
    mkdir /var/run/xl2tpd/
#### Local user (PAM//etc/passwd) authentication
To use local user accounts via pam (or /etc/passwd), and thus not having plain
text user passwords in a text file you have to do a few extra steps. Huge thanks
to `Sascha Scandella` for the hard work and troubleshooting.
In your `/etc/xl2tpd/xl2tpd.conf` add the following line:
    unix authentication = yes
and remove the following line:
    refuse pap = yes
In the file `/etc/ppp/options.xl2tpd` make sure you do not add the following
line (below it states to add it, but not if you want to use UNIX
Also in that file (`/etc/ppp/options.xl2tpd`) add the following extra line:
Change `/etc/pam.d/ppp` to this:
    auth    required        pam_nologin.so
    auth    required        pam_unix.so
    account required        pam_unix.so
    session required        pam_unix.so
Add the following to `/etc/ppp/pap-secrets`:
    *       l2tpd           ""              *
(And, skip the `chap-secrets` file below (adding users).)
#### Configuring PPP
Use your favorite editor to edit the following file:
Replace the contents with the following:
    mtu 1200
    mru 1000
    name l2tpd
    lcp-echo-interval 30
    lcp-echo-failure 4
  * ms-dns = The dns to give to the client. I use googles public DNS.
  * proxyarp = Add an entry to this systems ARP [Address Resolution Protocol] table with the IP address of the peer and the Ethernet address of this system. This will have the effect of making the peer appear to other systems to be on the local ethernet.
  * name l2tpd = is used in the ppp authentication file.
#### Adding users
Every user should be defined in the `/etc/ppp/chap-secrets` file. Below is an
example file.
    # Secrets for authentication using CHAP
    # client       server  secret                  IP addresses
    alice          l2tpd   0F92E5FC2414101EA            *
    bob            l2tpd   DF98F09F74C06A2F             *
  * client = username for the user
  * server = the name we define in the ppp.options file for xl2tpd
  * secret = password for the user
  * IP Address = leave to * for any address or define addresses from were a user can login.
#### Testing it
To make sure everything has the newest config files restart openswan and xl2tpd:
    systemctl restart openswan
    systemctl restart xl2tpd
On the client connect to the server IP address (or add a DNS name) with a valid
user, password and the shared secret. Test if you have internet access and which
IP you have (via for example . If it is the VPN servers IP
then it works.
If you experience problems make sure to check the client log files. Also, on
Arch Linux, the system log can be viewed by using `journalctl -f` (that emulates
`tail -f /var/log/syslog`). Arch Linux uses systemd logging. For more info about
systemd services, [see this page][14]
If you have your Raspberry Pi behind a NAT router, you might need to change your
%SERVERIP% to the internal IP of your Raspberry Pi (like instead
of your external IP address.
If you google the error messages you most of the time get a good answer.
Thanks to [Keith's article][15] for help with boot persistency.
   [1]: https://raymii.org/s/inc/img/arch_on_pi.jpg
   [2]: https://raymii.org/s/tutorials/IPSEC_L2TP_vpn_on_a_Raspberry_Pi_with_Arch_Linux.html
   [3]: https://raymii.org/s/tutorials/IPSEC_vpn_with_CentOS_7.html
   [4]: https://raymii.org/s/tutorials/IPSEC_L2TP_vpn_on_CentOS_-_Red_Hat_Enterprise_Linux_or_Scientific_-_Linux_6.html
   [5]: https://raymii.org/s/tutorials/IPSEC_vpn_with_Ubuntu_16.04.html
   [6]: https://raymii.org/s/tutorials/IPSEC_vpn_with_Ubuntu_15.10.html
   [7]: https://raymii.org/s/tutorials/IPSEC_vpn_with_Ubuntu_15.04.html
   [8]: https://raymii.org/s/tutorials/IPSEC_L2TP_vpn_with_Ubuntu_14.04.html
   [9]: https://raymii.org/s/tutorials/IPSEC_L2TP_vpn_with_Ubuntu_13.10.html
   [10]: https://raymii.org/s/tutorials/IPSEC_L2TP_vpn_with_Ubuntu_13.04.html
   [11]: https://raymii.org/s/tutorials/IPSEC_L2TP_vpn_with_Ubuntu_12.10.html
   [12]: https://raymii.org/s/tutorials/IPSEC_L2TP_vpn_with_Ubuntu_12.04.html
   [13]: https://www.digitalocean.com/?refcode=7435ae6b8212
   [14]: http://www.freedesktop.org/software/systemd/man/systemd.service.html
   [15]: https://smileykeith.com/2014/01/27/ipsec-l2tp-vpn-on-a-raspberry-pi-running-arch-linux/
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