Netopia 4752, Руководство администратора

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12-2 Administration Guide
Tunneling is a process of creating a private path between a remote user or private network and another private
network over some intermediate network, such as the IP-based Internet. A VPN allows remote offices or
employees access to your internal business LAN through means of encr yption allowing the use of the public
Internet to look “vir tually” like a private secure network. When two networks communicate with each other
through a network based on the Internet Protocol, they are said to be
tunneling through the IP network.
Unlike the phone company, private and public computer networks can use more than one protocol to carr y your
information over the wires. Three such protocols are in common use for tunnelling, Point-to-Point Tunnelling
Protocol (PPTP), Ascend Tunnel Management Protocol (ATMP), and IP Security (IPsec). The Netopia Router can
use any one.
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Point-to-Point Tunneling Protocol (PPTP) is an extension of Point-to-Point Protocol (PPP) and uses a client
and ser ver model. Netopia’s PPTP implementation is compatible with Microsoft’s and can function as
either the client (PAC) or the ser ver (PNS). As a client, a Netopia R-series router can provide all users on a
LAN with secure access over the Internet to the resources of another LAN by setting up a tunnel with a
Windows NT ser ver running Remote Access Ser vices (RAS) or with another Netopia Router. As a ser ver, a
Netopia R-series router can provide remote users a secure connection to the resources of the LAN over a
dial-up, cable, DSL, or any other type of Internet access. Because PPTP can create a VPN tunnel using the
Dial-Up Networking (DUN) (see
Dial-Up Networking for VPN on page 12-15) utility built into Windows 95, 98,
or NT, no additional client software is required.
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Ascend Tunnel Management Protocol (ATMP) is the protocol that is implemented in many Ascend routers.
ATMP is a simple protocol for connecting nodes and/or networks together over the Internet via a tunnel.
ATMP encapsulates IP or other user data without PPP headers within General Routing Encapsulation (GRE)
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
Transit Internetwork
Logical
Equivalent
Virtual Private Network