Overhead

VPN tunnels impose overhead for dial-in users: encryption algorithms may impact the performance of the user's system, there will be an increased protocol header overhead, authentication latency will increase, PPP and IP compression will perform poorly (compared to a direct link), and modem compression won't work at all.

Support issues

Replacing direct-dial links with VPN tunnels may produce some very painful faultfinding missions. Due to the complexity of VPN carrier networks, the opportunities for "hand-washing" are enormous.

Reconnection time

Using tunneling may increase the reconnection time for dial users. With the VPN carrier L2TP model, the client has to go through two authentication phases: one on contacting the VPN carrier POP, and another on contact with the enterprise Security Gateway.

Multimedia

Applications such as video conferencing only work acceptably over low latency links that can offer the required minimum throughput. Currently on the Internet, latency and throughput can vary alarmingly. Multi-channel data services, such as ISDN and XDSL solve this problem in the short-term, allowing the "data" channel to be used for VPN tunneling, and a separate "voice" channel to be used for business telephone calls or video conferencing.

Encryption

When using encryption to protect a tunnel, data compression is no longer achievable as encrypted data is not compressible. This means that hardware compression over a modem connection is not possible.

Impact of Virtual Private Networks

The impact of VPN goes beyond secure and cost-effective remote access. Currently emerging security technology and public key infrastructure...

As VPN technology matures, organizations will increasingly utilize public Internet services for LAN-to-LAN communications, intranets and other mission critical application service networks.
Service Impact

Reduces processing time

Requires less labor effort of people

Lowers the chance of applications being lost in the system

Allows for transfer of application between agencies

Conclusions

The success of VPN in the future depends mainly on industry dynamics. Most of the value in VPN lies in the potential for businesses to save money. Should the cost of long-distance telephone calls and leased lines continue to drop, fewer companies may feel the need to switch to VPN for remote access. Conversely, if VPN standards solidify and vendor products interoperate fully with other, the appeal of VPN should increase.

The success of VPN also depends on the ability of intranets and extranets to deliver on their promises. Companies have had difficulty measuring the cost savings of their private networks, but if it can be demonstrated that these provide significant value, the use of VPN technology internally may also increase.

References

Bird, T. (2001). Virtual Private Networks. Retrieved April 21, 2005, from Vpn.shmoo.com

Web site: http://vpn.shmoo.com/vpn/FAQ.html

Virtual Private Networks. (n.d). Retrieved April 20, 2005, from Cba.unomaha.edu

Web site: http://cba.unomaha.edu/faculty/garfathr/web/vpn_pros_cons.html

VPN FAQ. (2005). Retrieved April 21, 2005, from Pbcg.com

Web site: http://www.pbcg.net/pages/vpn_faq.htm