Product specifications

Chapter 6: Connection Management Efficient Networks
®
Router family
Command Line Interface Guide
Page 6-48 Efficient Networks
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Network (Layer-3) VPNs
Tunneling
Tunneling has been in existence for many years and recently has become the answer
to cutting long distance WAN access costs. This is what most of us think of as "VPN".
Tunneling uses some Layer-1 and Layer-2 technology already in place. It also uses a
public (or private) IP network to connect multiple sites together.
IP Network transport (public or private)
Using a public IP network to transport private LAN data would not have been practical
had there not been public IP network on which to transport data. Since the Internet is
a public IP network and is now accessible to a majority of users, it is now practical to
use it as the transport mechanism for private data.
Advantages
CHEAP: The most compelling reason for using the Internet for a VPN is that it can cut
long-distance charges dramatically. The common disadvantage of both Layer-1 and
Layer-2 transport is the cost of long distance. Internet long distance is FREE!
Easy to set up: Both networks must have tunneling equipment, but once that is in
place, connecting from one network to another is just like placing a phone call.
Flexible: Since it is not cost-prohibitive to install a new tunnel through the Internet,
new locations can be brought online quickly.
Disadvantages
No Quality of Service guarantees: The quality of the transport is usually NOT
guaranteed and we all know how the Internet can slow down at times. There can be
latency and slow throughput if the Internet slows down.
Protocol support: TCP/IP protocol is well suited for running effectively on error-prone
networks. However, protocols like Bridging, Appletalk, Novel IPX, and other LAN
protocols do not perform well on a highly latent and error-prone network like the
Internet.
Interpretability (standards): Current implementations of tunneling protocols are not
highly interoperable between vendors due to the young age of the technology.
However, there are several tunneling protocol standards that are settling in and this
will not remain an issue for long. The standardized protocols for tunneling are IPSec
and L2TP.