3com 3031 Instruccion De Instalación

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 VPN

gateway, which affects the load and scalability of the system.In addition, because 
LCP and NCP negotiations of PPP are very time sensitive, the efficiency of IP tunnel 
results in a series of problems, such as PPP session timeout. In contrast, a layer 3 
tunnel ends at the ISP gateway and PPP session ends at NAS, so it is unnecessary 
for the gateway at the user end to manage and maintain the status of every PPP 
session, thus improving system performance.

Generally, Layer 2 and Layer 3 tunnel protocols are used independently. However, 
if they are used together, for instance using L2TP and IPSec simultaneously, better 
performance and security can be provided for the users.

IP VPN is the emulation of leased line services (remote dial-up and DDN) of WAN 
equipment using IP facilities (including public Internet or private IP backbone 
network). IP VPN classification is based on:

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Operation mode

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Service Purpose

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Users not only install expensive devices and specified authentication tools, but also 
maintain complex VPN (e.g. channel maintenance, band width management, 
etc.). Networking in this way features high complexity and low ability of service 
extension.

In a network-based VPN, the maintenance of VPN is allocated to the ISP, although 
users are allowed to manage and control services to some extent. VPN functions 
are mainly fulfilled on the equipment at the network side. This type of service 
reduces the investments of the users, increases the flexibility and scalability of 
services, bringing profits to the ISP.

VPNs are also classified according to the types of service they provide:

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Intranet VPN: An intranet VPN, interconnects the remote branches of an 
enterprise through the public network, it is an extended or substitute form of 
traditional leased line or private networks.

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Access VPN: Access VPN provides a means to establish private connections with 
the intranet or extranet of enterprises through the public networks for those 
staff traveling on business, remote personnel and SOHO. Access VPN has two 
types: client-initiated VPN connections and NAS-initiated VPN connections.

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Extranet VPN: Extranet VPN extends an intranet to partners and clients through 
VPN so that different enterprises can build their VPNs using public networks.

VPNs are classified by the type of networking model that they use:

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Virtual Leased Line (VLL): VLL emulates the traditional leased line service with 
the help of the IP network and hence providing asymmetrical and inexpensive 
leased line service. For the users at both ends of the VLL, the VLL is similar to 
the traditional leased line.