L2TP Client: Windows

Windows 10

Windows 10 has a built in L2TP client, there are a couple of extra bits that may be needed to get this to work once you've set up the initial connections - there are two extra steps below regarding ipsec and CHAP.

Initial connection setup

1. Start
2. Control Panel (cog icon)
3. Network & Internet
4. VPN (link on left panel)
5. Add a VPN connection, with these details:
   • VPN Provider = built in
   • Connection Name: AAISP L2TP
   • Server name: l2tp.aa.net.uk
   • Type: L2TP (With certificate (we'll disable ipsec later))
   • username: your xxx@a.1 username
   • your password
6. Click save

You should then be able to connect and disconnect via the Network icon in your Start bar.

However, the following two steps may be needed too:

Enable CHAP

Once the connection has been created, ensure CHAP authentication is enabled:

1. Open Network and Sharing Centre
2. Click Change adapter settings
3. Find the L2TP connection, it will have whatever name you gave it
4. Right click the connection and choose Properties
5. Go to the Security Tab
6. Find the 'Authentication' section
7. Select the 'Allow these protocols' radio button
8. Ensure 'Challenge Handshake Authentication Protocol (CHAP)' is checked.

Disable IPsec

Windows 10 seems very keen on using IPsec with L2TP. To turn this off, in an Administrator Command Prompt do: (Click start, type cmd, press Ctrl-Shift-Enter)

SC STOP RASMAN    ; you may have to wait a bit for this to stop
SC QUERY RASMAN   ; ensure it is STOPPED
REG ADD HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Rasman\Parameters /v ProhibitIpSec /t REG_DWORD /d 1 /f
SC START RASMAN

Split tunnel routing

This is more of an advanced topic, and if you're looking in to this then you probably know what you're doing already!

It's possible to only send certain traffic over the L2TP and send the rest of your traffic over your normal internet connection.

You can do this by disabling the option to use the default gateway of the L2TP - this is a setting found in the TCPIP settings of the L2TP connection Adaptor settings:

1. Start
2. Control Panel (cog icon)
3. Network & Internet
4. VPN (link on left panel)
5. Change adaptor settings
6. Right-click on AA L2TP, click properties
7. Networking tab
8. Double click TCP/IP
9. Advanced
10. Untick 'Use default gateway on remote network

You can then use various commands to route specific traffic over the L2TP, eg, for example if you only want to send "81.187.30.81/32 over the L2TP, then you can use this PowerShell command:

Add-VpnConnectionRoute -ConnectionName "AA L2TP" -DestinationPrefix "81.187.30.81/32" -PassThru

You can then go to http://ip4.help.me.uk (which is hosted on that IP) and it will show your L2TP IP address.

Windows 7

This probably applies to Windows 8 too.

Connecting with Windows 7 is almost the same as the steps for Windows 10 above, except that the default connection settings don't work. You have to edit the connection properties and on the Security tab change:

1. 'Type of VPN:' to 'Layer 2 Tunneling Protocol with IPsec (L2TP/IPSec)' otherwise it only tries PPTP
2. 'Data encryption:' to 'Optional encryption (connect even if no encryption)'

Watch out if you are using IPv6. It seems that Win7 negotiates a non-routable IPv6 address with the LNS. You have to discard this address and manually configure one of your routed IPv6 addresses. ipconfig /release6 is your friend here.