Virtual Private Dial Networks (VPDNs) adopt special network encryption protocols to set up secure VPNs for enterprise customers over public networks. With VPDNs, overseas offices and telecommuting staff can obtain a network connection to their headquarter through a virtual encryption tunnel over public networks. Other users on the public networks cannot pass through the virtual tunnel to access internal resources on the enterprise network.

There are two ways to fulfill VPDN:

• NAS creating tunnel with VPDN gateway through tunneling protocol

  In this way, PPP connections of users are directly connected to gateway in an enterprise. By now, available tunnel protocols are L2F and L2TP.

  Its advantages are:

  • It is transparent to users.

  • Users access enterprise network by login once.

  • Enterprise network performs user authentication and address assignment without occupying public address.

  • Users can access network by a wide variety of platforms.

  This way of VPDN requires NAS that supports the VPDN protocol, and authentication system that supports VPDN attributes, with gateway generally adopting firewall or VPN dedicated server.

• Clients creating tunnel with VPDN gateway

  In this way, clients first establish connection with the Internet, and then channel connection with gateway through dedicated client software(such as L2TP client port supported by Win2000).

  Its advantages lie in:

  • No limit to the way and place of users accessing network

  • No need for ISPs involvement

  Its disadvantages are:

  Users need to install dedicated software (usually Win2000 platform), which limits platforms available for users.

There are two ways to fulfill VPDN:

• NAS creating tunnel with VPDN gateway through tunneling protocol

  The Network Access Server (NAS) directly connects the PPP connections of the customer to the VPDN gateway through the VPDN tunneling protocol, this establishing a tunnel with the VPDN gateway.

  Its advantages are:

  • It is transparent to users.

  • Users access enterprise network by login once.

  • Enterprise network performs user authentication and address assignment without occupying public address.

  • Users can access network by a wide variety of platforms.

  This way of VPDN requires NAS that supports the VPDN protocol, and authentication system that supports VPDN attributes, with gateway generally adopting firewall or VPN dedicated server.

• Clients creating tunnel with VPDN gateway

  In this way, clients first establish connection with the Internet, and then channel connection with gateway through dedicated client software.

  • Its advantages lie in:

    • No limit to the way and place of users accessing network

    • No need for ISPs involvement

  • Its disadvantages are:

    Users need to install dedicated software , which limits platforms available for users.

There are three types of VPDN tunneling protocol:

• Point-to-Point Tunneling Protocol (PPTP)
• Layer 2 Forwarding (L2F)
• Layer 2 Tunneling Protocol (L2TP)

Among them, L2TP is the most popular.

Nice way to create VPN between two remote location.

Thanks for sharing.