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Virtual Private Networks (VPNs) 10-123
the receiving side, an IPsec-compliant device decrypts each packet. The Netopia 4553 supports the more
secure Tunnel mode.
DES stands for Data Encryption Standard, a popular symmetric-key encryption method. DES uses a 56-bit
key. The Netopia 4553 offers IPsec DES encryption over the VPN tunnel.
When used to initiate the tunnelled connection, the Netopia 4553 is called a PPTP Access Concentrator (PAC, in
PPTP language), or a foreign agent (in ATMP language). When used to answer the tunnelled connection, the
Netopia Router is called a PPTP Network Server (PNS, in PPTP language) or a home agent (in ATMP language).
In either case, the Netopia Router wraps, or encapsulates, information that one end of the tunnel exchanges
with the other, in a wrapper called General Routing Encapsulation (GRE), at one end of the tunnel, and unwraps,
or decapsulates, it at the other end.
Configuring the Netopia Router for use with the different protocols is done through the console-based menu
screens. Each type is described in its own section:
■ "About PPTP Tunnels" on page 10-123
■ "About IPsec Tunnels" on page 10-127
■ "About ATMP Tunnels" on page 10-132
Your configuration depends on which protocol you (and the router at the other end of your tunnel) will use, and
whether or not you will be using the VPN client software in a standalone remote connection.
Note: You must choose which protocol you will be using, since you cannot both export PPTP and use ATMP, or
vice versa, at the same time.
Having both an ATMP tunnel and a PPTP export is not possible because functions require GRE and the router’s
PPTP export/server does not distinguish the GRE packets it forwards. Since it processes all of them, ATMP
tunneling is impaired. For example, you cannot run an ATMP tunnel between two routers and also have PPTP
exported on one side.
Summary
A Virtual Private Network (VPN) connects the components of one network over another network. VPNs
accomplish this by allowing you to tunnel through the Internet or another public network in a manner that
provides the same security and features formerly available only in private networks.
VPNs allow networks to communicate across an IP network. Your local networks (connected to the Netopia
Router) can exchange data with remote networks that are also connected to a VPN-capable router.
This feature provides individuals at home, on the road, or in branch offices with a cost-effective and secure way
to access resources on remote LANs connected to the Internet with Netopia Routers. The feature is built
around three key technologies: PPTP, IPsec, and ATMP.
About PPTP Tunnels
To set up a PPTP tunnel, you create a Connection Profile including the IP address and other relevant information
for the remote PPTP partner. You use the same procedure to initiate a PPTP tunnel that terminates at a remote
PPTP server or to terminate a tunnel initiated by a remote PPTP client.