ZyXEL Communications USG40 User Manual page 358

• PPPoE does not usually require any special configuration of the modem.
PPTP is used to set up virtual private networks (VPN) in unsecured TCP/IP environments. It sets up
two sessions.
The first one runs on TCP port 1723. It is used to start and manage the second one.
1
The second one uses Generic Routing Encapsulation (GRE, RFC 2890) to transfer information
2
between the computers.
PPTP is convenient and easy-to-use, but you have to make sure that firewalls support both PPTP
sessions.
Layer 2 Tunneling Protocol (L2TP) was taken from PPTP of Microsoft and Cisco's L2F (Layer 2
Forwarding technology), so LT2P combines PPTP's control and runs over a faster transport protocol,
UDP, although it may be a bit more complicated to set up.
It supports up to 256 bit session keys using the IPSec protocol. When security is a priority, L2TP is
a good option as it requires certificates unlike PPTP.
It uses the following ports: UDP 500, Protocol 50, UDP 1701 and UDP 4500.
Chapter 10 Interfaces
ZyWALL/USG Series User's Guide
358