Protocols, Protocols, and More Protocols!
Because the functions provided by a VPN include tunneling, data integrity, and authentication, it makes sense that a VPN is not created using a single protocol. Instead, several protocols can be used to create a VPN, each performing a particular function. In this section the following protocols are briefly examined:
Internet Protocol Security (IPSec) Point-to-Point Tunneling Protocol (PPTP) Layer Two Tunneling Protocol (L2TP)
For the most part, only IPSec should be a major factor in VPNs in the coming years. PPTP was used by Windows NT 4.0 as part of its VPN package, and L2TP has replaced it in Windows 2000 and Windows XP VPNs. L2TP is basically just the PPTP protocol combined with the L2F protocol developed by Cisco. However, most VPN vendors are using the IPSec protocols instead, which are described in greater detail than PPTP and L2TP in this chapter. The IPSec protocols incorporate some of the security mechanisms that were originally designed to be included in IPv6 but have been adapted for use in the existing IPv4 network.
Note
Before you adopt a particular VPN solution, you should determine if the connection will be used by PDAs, Pocket PCs, or smartphones. Many of these devices do not include integrated VPN support, but in some cases updates to the operating system or third-party software does provide this functionality as an additional feature. IPSec is the most common VPN protocol supported by hand-held devices.
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