L2Tp Roaming Clients With Pre-Shared Keys - D-Link NetDefend DFL-210 User Manual

9.2.5. L2TP Roaming Clients with
Pre-Shared Keys
Also review Section 9.6, "CA Server Access", which describes important considerations for
certificate validation.

9.2.5. L2TP Roaming Clients with Pre-Shared Keys

Due to the inbuilt L2TP client in Microsoft Windows, L2TP is a popular choice for roaming client
VPN scenarios. L2TP is usually encapsulated in IPsec to provide encryption with IPsec running in
transport mode instead of tunnel mode. The steps for L2TP over IPsec setup are:
1. Create an IP object (let's call it l2tp_pool) which defines the range of IP addresses which can be
handed out to clients. The range chosen could be of two types:
• A range taken from the internal network to which clients will connect. If the internal
network is 192.168.0.0/24 then we might use the address range 192.168.0.10 to
192.168.0.20. The danger here is that an IP address might be accidentally used on the
internal network and handed out to a client.
• Use a new address range that is totally different to any internal network. This prevents any
chance of an address in the range also being used on the internal network.
2. Define two other IP objects:
• ip_ext which is the external public IP address through which clients connect (let's assume
this is on the ext interface).
• ip_int which is the internal IP address of the interface to which the internal network is
connected (let's call this interface int).
3. Define a Pre-shared Key for the IPsec tunnel.
4. Define an IPsec Tunnel object (let's call this object ipsec_tunnel) with the following
parameters:
• Set Local Network to ip_ext (specify all-nets instead if NetDefendOS is behind a NATing
device).
• Set Remote Network to all-nets.
• Set Remote Endpoint to none.
• For Authentication select the Pre-shared Key object defined in the first step.
• Set Encapsulation Mode to Transport.
• Select the IKE and IPsec algorithm proposal lists to be used.
• Enable the routing option Dynamically add route to the remote network when tunnel
established. If all-nets is the destination network, the option Add route for remote network
should be disabled.
5. Define an PPTP/L2TP Server object (let's call this object l2tp_tunnel) with the following
parameters:
• Set Inner IP Address to ip_int.
• Set Tunnel Protocol to L2TP.
Note: The system time and date should be correct
The NetDefendOS date and time should be set correctly since certificates have an
expiry date and time.
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Chapter 9. VPN