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Introduction to VPDN- Virtual private dial-up networks

Today I am going to talk about VPDN. VPDN stands for Virtual private dial-up networks and used to carry private data securely over the internet media.VPDNs preserve the identical security and management strategies as a private network, though delivering a profitable technique for P2P connections among remote users and a central network.

Virtual private dial-up networks operators associate to a nearby access server, which is frequently situated at an ISP on their POP. Data is securely accelerated from the access server to the private network over the Internet, delivering a cost-effective technique of contact among remote clients and the private network.

Here in the case of VPDN, client can subcontract accountability for the data technology (IT) infrastructure to an ISP that preserves the modems and the remote users dial in to, the access servers, and the internetworking capability. The client is then accountable only for authenticating users and preserving the private network.

Fig 1.1- VPDN Network Deployment
Whenever the PPP client comes into the picture, it tries to dial in to an ISP access server, called the Network Access Server (NAS). The Network Address Server regulates whether it should advance that PPP session on to the WAN device or access server that assists as the point of communication for the private network, the tunnel server. The tunnel server authenticates the user and starts PPP dialogues. Once PPP setup is complete, all frames that are sent among the client and the tunnel server pass through the NAS.

VPDN uses various tunneling protocols like L2TP, L2TPv3, Layer 2 Forwarding, PPTP to create the tunnel between Tunnel server and Client. This communication will happen over the shared media like Internet. 

Let’s talk about the two tunneling techniques and the comparison between Layer 2 Forwarding and L2TP. L2F don’t have the capability of Attribute Value and Flow control while it is taken care in L2TP. Features like Load sharing on tunnel server, Multihop support, primary and backup tunnels, DNS support, Multilink PPP support are there on Layer 2 Forwarding and L2TP both.

In our next article, we will discuss about the configuration of various VPDN techniques.