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Found at: raymii.org:70/IPSEC_L2TP_vpn_with_Ubuntu_13.04.txt

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Title       : 	IPSEC L2TP VPN on Ubuntu 13.04 with OpenSwan, xl2tpd and ppp
Author      : 	Remy van Elst
Date        : 	01-12-2014
URL         : 	https://raymii.org/s/tutorials/IPSEC_L2TP_vpn_with_Ubuntu_13.04.html
Format      : 	Markdown/HTML
This is a guide on setting up an IPSEC/L2TP vpn server with Ubuntu 13.04 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][1]
  * [CentOS 7, Scientific Linux 7 or Red Hat Enterprise Linux 7 (IKEv2,no L2TP)][2]
  * [CentOS 6, Scientific Linux 6 or Red Hat Enterprise Linux 6][3]
  * [Ubuntu 16.04, (IKEv2,no L2TP)][4]
  * [Ubuntu 15.10, (IKEv2,no L2TP)][5]
  * [Ubuntu 15.04, (IKEv2,no L2TP)][6]
  * [Ubuntu 14.04 LTS][7]
  * [Ubuntu 13.10][8]
  * [Ubuntu 13.04][9]
  * [Ubuntu 12.10][10]
  * [Ubuntu 12.04 LTS][11]

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.

You can also sponsor me by getting a Digital Ocean VPS. With this referral link you'll get $100 credit for 60 days.

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 need to use it together with IPSec.
To work trough this tutorial you should have:
  * 1 ubuntu 13.04 server with at least 1 public IP address and root access
  * 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.
If you are not running Ubuntu 13.04 you might have to compile the packages
manually because openswan and xl2tpd in the older repositories seem to have
critical bugs which make this all fail.
I do all the steps as the root user. You should do to, but only via * -i* or *
su -*. Do not allow root to login via SSH!
#### Install ppp openswan and xl2tpd
First we will install the required packages:
    apt-get install openswan xl2tpd ppp 
The openswan installation will ask some questions, this tutorial works with the
default answers (just enter through it).
If you do not have lsof installed you also need to install that, otherwise the
ipsec verify will fail:
    apt-get install lsof
#### 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 -t nat -A POSTROUTING -j SNAT --to-source %SERVERIP%
Replace %SERVERIP% with the external IP of your VPS.
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
Now apply 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
And apply them:
    sysctl -p
##### Persistent settings via /etc/rc.local
To make sure this keeps working at boot you might want to add the following to
    for vpn in /proc/sys/net/ipv4/conf/*; do echo 0 > $vpn/accept_redirects; echo 0 > $vpn/send_redirects; done
    iptables -t nat -A POSTROUTING -j SNAT --to-source %SERVERIP%
Add it before the `exit 0` line and replace %SERVERIP% with the external IP of
your VPS.
#### Configure Openswan (IPSEC)
Use your favorite editor to edit the following file:
Replace the contents with the following:
(Most lines have a comment below it explaining what it does.)
    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.
    conn L2TP-PSK-noNAT
        #shared secret. Use rsasig for certificates.
        #Disable pfs
        #start at boot
        #Only negotiate a conn. 3 times.
        #because we use l2tp as tunnel protocol
        #fill in server IP above
Replace %SERVERIP% with the external IP of your server.
**Do note that the config file has changed with this Ubuntu release. If you have
upgraded Ubuntu or followed an earlier tutorial, make sure you change the config
for ipsec.**
##### The shared secret
The shared secret is defined in the `/etc/ipsec.secrets` file. Make sure it is
long and random:
    %SERVERIP%  %any:   PSK "69EA16F2C5DCED8B29E74A7D1B0FE99E69F6BDCD3E44"
##### Verify IPSEC Settings
Now to make sure IPSEC works, execute the following command:
    ipsec verify
My output looks like this:
    Checking your system to see if IPsec got installed and started correctly:
    Version check and ipsec on-path                                 [OK]
    Linux Openswan U2.6.38/K3.8.0-19-generic (netkey)
    Checking for IPsec support in kernel                            [OK]
     SAref kernel support                                           [N/A]
     NETKEY:  Testing XFRM related proc values                      [OK]
    Checking that pluto is running                                  [OK]
     Pluto listening for IKE on udp 500                             [OK]
     Pluto listening for NAT-T on udp 4500                          [OK]
    Checking for 'ip' command                                       [OK]
    Checking /bin/sh is not /bin/dash                               [WARNING]
    Checking for 'iptables' command                                 [OK]
    Opportunistic Encryption Support                                [DISABLED]
The `/bin/sh` and `Opportunistic Encryption` warnings can be ignored. The first
one is a openswan bug and the second one causes xl2tpd to trip.
#### 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
**Do note that the config file has changed with this Ubuntu release. If you have
upgraded Ubuntu or followed an earlier tutorial, make sure you change the config
for 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:
    /etc/init.d/ipsec restart 
    /etc/init.d/xl2tpd restart
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 and the
ubuntu `/var/log/syslog` and `/var/log/auth.log` files. If you google the error
messages you most of the time get a good answer.
   [1]: https://raymii.org/s/tutorials/IPSEC_L2TP_vpn_on_a_Raspberry_Pi_with_Arch_Linux.html
   [2]: https://raymii.org/s/tutorials/IPSEC_vpn_with_CentOS_7.html
   [3]: https://raymii.org/s/tutorials/IPSEC_L2TP_vpn_on_CentOS_-_Red_Hat_Enterprise_Linux_or_Scientific_-_Linux_6.html
   [4]: https://raymii.org/s/tutorials/IPSEC_vpn_with_Ubuntu_16.04.html
   [5]: https://raymii.org/s/tutorials/IPSEC_vpn_with_Ubuntu_15.10.html
   [6]: https://raymii.org/s/tutorials/IPSEC_vpn_with_Ubuntu_15.04.html
   [7]: https://raymii.org/s/tutorials/IPSEC_L2TP_vpn_with_Ubuntu_14.04.html
   [8]: https://raymii.org/s/tutorials/IPSEC_L2TP_vpn_with_Ubuntu_13.10.html
   [9]: https://raymii.org/s/tutorials/IPSEC_L2TP_vpn_with_Ubuntu_13.04.html
   [10]: https://raymii.org/s/tutorials/IPSEC_L2TP_vpn_with_Ubuntu_12.10.html
   [11]: https://raymii.org/s/tutorials/IPSEC_L2TP_vpn_with_Ubuntu_12.04.html
   [12]: https://www.digitalocean.com/?refcode=7435ae6b8212
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