ZyXEL Communications SBG5500 Series User Manual page 162

Chapter 10 VPN
PPTP sets up two sessions and uses Generic Routing Encapsulation (GRE, RFC 2890) to transfer
information between the computers. It is convenient and easy-to-use, but you have to make sure that
firewalls support both PPTP sessions.
PPTP works on a client-server model and is suitable for remote access applications. For example, an
employee (A) can connect to the PPTP VPN gateway (X) as a PPTP client to gain access to the
company network resources from outside the office. When you connect to a remote network (B)
through a PPTP VPN, all of your traffic goes through the PPTP VPN gateway (X).
Figure 130 PPTP VPN Example
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L2TP VPN
The Layer 2 Tunneling Protocol (L2TP) works at layer 2 (the data link layer) to tunnel network traffic
between two peers over another network (like the Internet). In L2TP VPN, an IPsec VPN tunnel is
established first and then an L2TP tunnel is built inside it.
L2TP VPN lets remote users use the L2TP and IPsec client software included with their computers'
operating systems to securely connect to the network behind the SBG. The remote users do not need
their own IPsec gateways or VPN client software.
Figure 131 L2TP VPN Overview
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