3com 3031 Instruccion De Instalación

This chapter tells you the following:

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Introduction to VPN and Dynamic VPN

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How To Configure Dynamic VPNs

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Typical Example of DVPN Configuration

In present VPN (virtual private network) networking solutions, Layer-3 VPN is often 
in GRE (generic routing encapsulation) tunneling and MPLS (multi-protocol label 
switching) /BGP (boarder gateway protocol) VPN mode. The latter is often used in 
backbone forwarding layer, while the former is in access layer. The existing GRE 
tunneling solution has these disadvantages: 

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Complicated networking and configuration. Conventionally, point-to-point 
tunneling solution is used. If N nodes need to be interconnected in VPN mode, 
then N 

× (n - 1) /2 links should be set up in the network. 

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Poor maintainability and scalability. If you want to add nodes or modify 
configurations of some nodes in a finished VPN network, you should also 
modify configurations of other nodes based on the newly-added ones. 
Maintenance cost is high. 

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Fail to traverse NAT (network address translation) gateway. In conventional GRE 
tunneling mode, if NAPT (network address port translation) gateways work as 
egress, one private IP address must correspond to one public IP address, which 
may occupy enormous public IP addresses. So GRE tunneling is unfit for NAT 
gateway. 

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Unfit for dynamic IP. Conventional GRE tunneling is based on fixed IP addresses 
and it cannot set up VPN for dialup subscribers. 

Dynamic VPN (DVPN) provides NBMA (non-broadcast multiple access) tunneling 
mechanism and the client/server structure can effectively solve the 
above-mentioned defects of conventional VPN. When multiple access devices in 
different private networks are connected into one VPN through backbone 
network, NAMA links can be set up between tunnels in a same VPN and one 
device can have multiple tunnels for different VPNs. So one device supports 
multiple VPNs. Characteristics of DVPN:

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It supports both GRE tunneling and UDP tunneling, so it can traverse NAPT 
gateway. It solves the problems when private IP addresses are connected to 
VPN network through NAPT gateway or other kinds of routers. 

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It uses dynamic IP addresses to build VPNs. To build tunnels within a VPN in this 
mode, you only need to specify IP address for the server, regardless of the IP 
addresses for clients. It is applicable to general dialup and xDSL dialup 
applications which are based on dynamic IP addresses.