Справочник Пользователя для Netopia 4000-Series

protocol over IP. ATMP is more efficient than PPTP for network-to-network tunnels.

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IPsec stands for IP Security, a set of protocols that suppor ts secure exchange of IP packets at the IP layer. 
IPsec is deployed widely to implement Vir tual Private Networks (VPNs). IPsec suppor ts two encr yption 
modes: Transpor t and Tunnel. Transpor t mode encr ypts only the data por tion (payload) of each packet, but 
leaves the header untouched. The more secure Tunnel mode encr ypts both the header and the payload. On 
the receiving side, an IPsec-compliant device decr ypts each packet. The Netopia Firmware Version 5.4 
suppor ts the more secure Tunnel mode.

DES stands for Data Encr yption Standard, a popular symmetric-key encr yption method. DES uses a 56-bit 
key. The Netopia Firmware Version 5.4 offers IPsec DES encr yption over the VPN tunnel.

When used to initiate the tunnelled connection, the Router 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 Ser ver (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:

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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.

You must choose which protocol you will be using, since you cannot both expor t PPTP and use ATMP, or 

vice versa, at the same time.

Having both an ATMP tunnel and a PPTP expor t is not possible because functions require GRE and the router’s 
PPTP expor t/ser ver does not distinguish the GRE packets it for wards. 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 
expor ted on one side.

A Vir tual 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.