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Virtual Private Networks
(VPNs)
Background
information about VPN's
VPNs offer the ability to have private
communications over public networks such as the Internet. The term
refers to a combination of technologies and techniques that secure
the communications between two end points by setting up a secure
tunnel impervious to eavesdropping and interference.
* The following information is
intended to be a reference for products and services related to
mobile PC computing over PCS networks. Neither Intel nor
the Mobile Data Initiative endorse the products or companies listed
below. This information has been submitted by the companies listed
for informational purposes only. No guarantee is made about its
accuracy.
A
remote approach using the Internet connection already in place
Purchasing and maintaining modem pools
to support remote workers is becoming a major expense for corporations.
In addition, many of the calls are long distance. Since most of
these same companies already have a connection to the Internet,
an attractive approach is to use this Internet connection for remote
workers to access corporate resources. Rather than dial into the
corporation, remote workers dial into a local Internet service provider
and then traverse the Internet to reach their corporate network.
Since many of the larger ISPs have points of presence in a large
number of cities, remote workers need only make a local call from
almost anywhere. And this approach can even work when workers travel
or work abroad. For international access, using the Internet can
provide much more reliable connections than making international
modem calls.
Using the Internet for remote access
eliminates both the expense of the modem pool as well as the associated
long distance charges. But it does raise questions of security and
performance. And it does require additional equipment and software
at the corporation and possibly additional bandwidth to the Internet.
Fortunately, the technology and service options for addressing both
security and performance are expanding rapidly. Standards to address
interoperability between vendors are beginning to stabilize as well.
The
two types of VPNs
The key technology area that addresses
remote access via the Internet is called virtual private networking
(VPN). VPNs are used in either of two ways. In one case, the tunnel
through the Internet is between two private networks, such as corporate
headquarters on one end and a remote office on the other, or between
a company and a partner company. In the latter case the management
of the tunnel on each end is performed by a dedicated VPN server
or by the existing Internet firewall. In fact, VPN functionality
can be thought of as an enhanced firewall function. This type of
VPN is called an extranet.
The other way of using VPNs is to connect
an individual mobile computer (workstation) across the Internet
to a private network. Here the VPN function is implemented as software
within the mobile computer. This computer can then use a local dial-up
connection to access the Internet and reach the private network.
Figure 1 shows the two different types of VPNs. There is also a
variation on this last approach where the individual workstation
makes a connection to an intermediary system, e.g. ISP, which then
manages the creation of the tunnel on behalf of the workstation.
Figure 1: Two types of VPNs.
In a VPN connection, the following
sequence of steps occur:
- The two end points first authenticate
themselves to each other.
- The VPN server can determine what
services the workstation has permission to access, and can control
subsequent traffic accordingly. This step is called authorization.
- Once the tunnel has been created,
the tunnel endpoints add special headers to packets addressed
for the other end of the tunnel, encrypt the original packet and
header and encapsulate all this information in new IP packets.
The internal headers provide authentication information at the
packet level, and also ensure that any tampering with the data
can be detected.
Figure 2: Secure tunnel with
a VPN.
Connection
options
When traveling with a mobile computer,
there are a number of ways that you can take advantage of VPN technology
to establish connections to your home networks:
Modem connection to local ISP.
You can use your PC Card modems to make traditional landline
connections to a local ISP, establish a PPP session and then proceed
to establish a VPN connection across the Internet.
Circuit-switched cellular connection
to local ISP. This approach is almost the same as using a
landline connection, except it is done either through an analog
or circuit-switched data connection.
Circuit-switched cellular connection
directly to the Internet. Rather than connecting to an ISP
via a modem gateway, you connect through a direct digital connection
to the Internet. Such services are forthcoming.
VPN
availability
VPN technology is not only available
today from companies specializing in VPNs,but also from operating
system vendors (e.g. Microsoft), traditional firewall vendors, and
possibly even router vendors in the future. There is limited interoperability
between products from different vendors today, since standards are
only now being finalized, so you will most likely need software
from the same vendor for both end points of your tunnels. Key standards
to watch are IPsec (secure IP), SOCKS and Layer 2 Tunneling Protocol
(L2TP). L2TP is a new standard that will combine attributes of Microsoft's
Point to Point Tunneling Protocol (PPTP) and Cisco's L2F (layer
2 forwarding.)
Wireless carriers are expected to provide
increasing options for connecting to the Internet. These options
will work hand in hand with VPN technologies to allow convenient
remote access to private networks from anywhere in the world. Anybody
traveling with both a mobile computer and a cellular telephone will
find it easier and easier to remain connected to their home organization.
Informational links about virtual private
networks:
Here are some links to companies that
offer VPN products:
Here are link to more information on
VPNs:
Strategic
Network "Putting VPNs to Work for Small Businesses and Offices"
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