IPSec-VPN on Stock Kernel

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Attention: What ever you do, you do it on your own risk



You have to have firmware 1.34 already installed and opened for telnet access. If not, you can find a guide here: Open Stock Firmware LS-XHL

For Firmwares before 1.34 this also may work, but it's unknown if the IPSEC-XL2TP Packages are also in there.

What's the aim ?

The aim is to realize a VPN-Server that uses L2TP-IPSec as tunneling technology.

Why this, and not PPTP ? The issue with PPTP is, that it needs MPPE support within the kernel, which is simply not there.

Therefore we are going to use IPSec & L2TP, as they are more secury in most scenarios in any way.

What is needed ?

The good news are: everything is already on the box, you don't have to install any external software-package at all.

The bad news: The packages are configured to be used for a service called PocketU (only in Japan). As a matter of fact all boxes outside of Japan are not using those things at all.

As a general guidline for an IPSec-L2TP Server we need: IPSec - Package (here OpenSwan with pluto), an IPSec-Configuration and a tunnel-configuration L2TP - Package (here xl2tp), and xl2tp-Configuration and ppp.xl2tp options

How does it work

The VPN works as follows:

1) An IPSec tunnel will be opened (using a preshared-key or certificates)

2) Within the tunnel L2TP is used to authenticate a user and do IP-adressing with PPP in there


Needed files to be touched / modified:







As all these files are already there, make sure, you are backing them up.

Configuring IPSec: Modify /etc/ipsec.conf to enable NAT-Traversal (NAT-T) and to define private networks:

 # basic configuration
 config setup
    # Debug-logging controls:  "none" for (almost) none, "all" for lots.
    # klipsdebug=none
    # plutodebug=all
    # Enable this if you see "failed to find any available worker"
 #You may put your configuration (.conf) file in the "/etc/ipsec.d/" and uncomment this.
    include /etc/ipsec.d/l2tp.conf

Based on this we are adding in /etc/ipsec.d/ a file called l2tp.conf to configure our connection:

  conn L2TP-PSK
       left=YOUR.LS.IP.ADDR       #Put the address of your linkstation here
       #leftnexthop=              #Put your (NAT)gateway address here

Now let's define secrets (preshared-key in this case) for the tunnel in /etc/ipsec.d/l2tp.secrets

  : PSK "PRESHARED-KEY" # you can add addresses before the ":" to define for which addresses this key is used

This should be sufficient for IPSec itself. You could try to start this with /etc/init.d/ipsec start

For L2TP we need to modify the file /etc/xl2tpd/xl2tpd.conf

    listen-addr = YOUR.LS:IP.ADDR   #Put your Linkstation-IP Address here
    ; debug tunnel = yes
    ; debug packet = yes
  [lns default]
    ip range = 192.168.XX.YYY-192.168.XX.ZZZ  # Address-range for clients
    local ip = YOUR.LS:IP.ADDR   #Put your Linkstation-IP Address here
    require chap = yes
    refuse pap = yes
    require authentication = yes
    pppoptfile = /etc/ppp/options.xl2tpd
    length bit = yes
    ppp debug = yes