The Types of VPN protocols

Internet uses the PPP-point-to-point protocol for remote access. VPN technology has incorporated additional functionality into PPP creating different protocols like PPTP-Point-to-point tunneling protocol,

L2TP-Layer-2 tunneling protocol and IPSec- IP security protocol. The diversity in VPN protocols is to cater to different requirements. Some protocols cater to remote access VPN connections from mobile users or branch offices that use a local ISP. Other protocols cater to communication between 'LAN-to-LAN'. PPTP, L2TP and L2F-Layer two forwarding have been developed for dial-up VPN's where as IPSec caters to 'LAN-to-LAN' solutions

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PPTP- Point-to-Point Tunneling Protocol

PPTP is one of VPN's first protocols built on PPP to provide remote access for VPN solutions. PPTP encapsulates PPP packets using GRE-Generic routing Protocol. This had been modified to give PPTP the flexibility of handling protocols other than IP like IPX-Internet Packet Exchange, and NetBEUI- Network basic input/output system extended user interface. PPTP uses authentication mechanisms within PPP, i.e. PAP-Password Authentication Protocol. Various other authentication and security mechanism have been developed by Microsoft and is utilized in its Operating System software.

L2F- Layer Two Forwarding Protocol

This was designed to tunnel data from corporate sites to their respective users. A protocol primarily implemented in CISCO products, it differs from PPTP in a way that it does not depend on IP. This could work on alternate media like frame relays or ATM-Asynchronous transfer Mode. L2F accepts other authentication mechanisms and allows tunnels to s upport more than one connection. L2F uses PPP for authentication of remote user. The authentication is done twice, one at the ISP and the second at the gateway to the connecting LAN. It is also a Layer-2 protocol and handles IPX and NetBEUI as well.

L2TP - Layer Two Tunneling Protocol

The best features of PPTP and L2F were combined to form L2TP. It exists in the second layer (data link) of the OSI-Open Systems Interconnect model and so its name L2TP. Approved by IETF L2TP transport is defined for packet media, Frame relay, ATM and X.25 (Standard for packet switching networks defining layers 1, 2 and 3 of the OSI model). It has its own tunneling protocol and uses PPP's PAP and other advanced mechanisms for authentication. Its encryption method is based on that of IPSec.

Internet Protocol Security (IPSec)

IPSec is a complete VPN protocol solution. Existing in the third layer of the OSI model it uses the IKE-Internet Key Exchange to exchange and manage cryptographic keys used in a data encryption session. IPSec uses a number of encryption technologies to provide confidentiality and data integrity. IPSec allows the sender to authenticate/encrypt or authenticate and encrypt each IP packet. For this it uses two modes either of which can be chosen dependent of situations of security and traffic.

Transport mode for authentication and encryption of the transport segment of an IP packet
Tunnel mode authenticates and encrypts the whole IP packet.

IPSec's strong security measures are designed mainly for IP packets and cannot handle multi-protocol non-IP network environments like NetBEUI or IPX.

VPN is a virtual environment and its advantage is that it is not dependent entirely on physical setup for its organizational needs but on its logical setup. This is its boon and its bane as well.

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