Tunneling: Remote-Access

In a remote-access VPN, tunneling normally takes place using PPP. Part of the TCP/IP stack, PPP is the carrier for other IP protocols when communicating over the network between the host computer and a remote system. Remote-access VPN tunneling relies on PPP.

Each of the protocols listed below were built using the basic structure of PPP and are used by remote-access VPNs.

• L2F (Layer 2 Forwarding) - Developed by Cisco, L2F will use any authentication scheme supported by PPP.

• PPTP (Point-to-Point Tunneling Protocol) - PPTP was created by the PPTP Forum, a consortium which includes US Robotics, Microsoft, 3COM, Ascend and ECI Telematics. PPTP supports 40-bit and 128-bit encryption and will use any authentication scheme supported by PPP.

• L2TP (Layer 2 Tunneling Protocol) - L2TP is the product of a partnership between the members of the PPTP Forum, Cisco and the IETF (Internet Engineering Task Force). Combining features of both PPTP and L2F, L2TP also fully supports IPSec.

L2TP can be used as a tunneling protocol for site-to-site VPNs as well as remote-access VPNs. In fact, L2TP can create a tunnel between:

• Client and router
• NAS and router
• Router and router

The truck is the carrier protocol, the box is the encapsulating protocol and the computer is the passenger protocol.

Think of tunneling as having a computer delivered to you by UPS. The vendor packs the computer (passenger protocol) into a box (encapsulating protocol) which is then put on a UPS truck (carrier protocol) at the vendor's warehouse (entry tunnel interface). The truck (carrier protocol) travels over the highways (Internet) to your home (exit tunnel interface) and delivers the computer. You open the box (encapsulating protocol) and remove the computer (passenger protocol). Tunneling is just that simple!

As you can see, VPNs are a great way for a company to keep its employees and partners connected no matter where they are.

For more information on VPNs and related topics, check out the links on the next page.