L2Tp Servers - D-Link DFL-1660 User Manual

9.5.2. L2TP Servers

A common problem with setting up PPTP is that a router and/or switch in a network is blocking
TCP port 1723 and/or IP protocol 47 before the PPTP connection can be made to the NetDefend
Firewall. Examining the log can indicate if this problem occurred, with a log message of the
following form appearing:
Error PPP lcp_negotiation_stalled ppp_terminated
Example 9.10. Setting up a PPTP server
This example shows how to setup a PPTP Network Server. The example assumes that certain address objects in
the NetDefendOS address book have already been created.
It is necessary to specify in the address book, the IP address of the PPTP server interface, an outer IP address
(that the PPTP server should listen to) and an IP pool that the PPTP server will use to give out IP addresses to
the clients from.
Command-Line Interface
gw-world:/> add Interface L2TPServer MyPPTPServer
Web Interface
1. Go to: Interfaces > PPTP/L2TP Servers > Add > PPTP/L2TP Server
2. Enter a name for the PPTP Server, for example MyPPTPServer
3. Now enter:
• Inner IP Address: lan_ip
• Tunnel Protocol: PPTP
• Outer Interface Filter: any
• Outer Server IP: wan_ip
4. Under the PPP Parameters tab, select pptp_Pool in the IP Pool control
5. Under the Add Route tab, select all_nets from Allowed Networks
6. Click OK
Use User Authentication Rules is enabled as default. To be able to authenticate the users using the PPTP
tunnel it is required to configure NetDefendOS Authentication Rules but that will not be covered in this example.
9.5.2. L2TP Servers
Layer 2 Tunneling Protocol (L2TP) is an IETF open standard that overcomes many of the problems
of PPTP. Its design is a combination of Layer 2 Forwarding (L2F) protocol and PPTP, making use
of the best features of both. Since the L2TP standard does not implement encryption, it is usually
implemented with an IETF standard known as L2TP/IPsec, in which L2TP packets are encapsulated
by IPsec.
The client communicates with a Local Access Concentrator (LAC) and the LAC communicates
across the Internet with a L2TP Network Server (LNS). The NetDefend Firewall acts as the LNS.
The LAC tunnels data, such as a PPP session, using IPsec to the LNS across the Internet. In most
cases the client will itself act as the LAC.
L2TP is certificate based and therefore is simpler to administer with a large number of clients and
ServerIP=lan_ip
Interface=any
IP=wan_ip
IPPool=pp2p_Pool
TunnelProtocol=PPTP
AllowedRoutes=all-nets
464
Chapter 9. VPN