Chapter 9 Interfaces
ZyWALL ATP Series User’s Guide
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PPPoE/PPTP/L2TP Overview
Point-to-Point Protocol over Ethernet (PPPoE, RFC 2516) and Point-to-Point Tunneling Protocol (PPTP, RFC
2637) are usually used to connect two computers over phone lines or broadband connections. PPPoE is
often used with cable modems and DSL connections. It provides the following advantages:
• The access and authentication method works with existing systems, including RADIUS.
• You can access one of several network services. This makes it easier for the service provider to offer
the service
• 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.
1
The first one runs on TCP port 1723. It is used to start and manage the second one.
2
The second one uses Generic Routing Encapsulation (GRE, RFC 2890) to transfer information 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.
