This makes L2TP/IPSec difficult to translate when using Network Address Translation (NAT). Additionally, the IPSec encryption used with L2TP encrypts the UDP header, the part of the IP packet that contains the destination UDP port number (usually UDP port 1701).

This adds complexity to the implementation and is generally perceived as a disadvantage, compared to the simplicity of PPTP, especially in small companies that would not normally implement a PKI. To implement L2TP, you need a certificate infrastructure in place. L2TP offers these improvements at a cost, however. The authentication process is protected by encryption through IPSec so that username and password information receives an extra level of security. L2TP/IPSec provides increased encryption strength when compared to that provided by PPTP. Layer Two Tunneling Protocol with Internet Protocol Security (L2TP/IPSec) combines the benefits of PPTP with those of Cisco’s Layer Two Forwarding (L2F). Microsoft’s PPTP uses the Microsoft Point to Point Encryption (MPPE) protocol for encryption. The protocol is an extension of the Generic Route Encapsulation (GRE) protocol with a control mechanism that operates on TCP port 1723.

PPTP includes provisions for encryption and compression. The current implementation of PPTP (used in Windows Server 2003) is PPTP v2. After several vulnerabilities were discovered in Microsoft s original implementation of PPTP, they revamped it and released version 2 of the protocol. PPTP was introduced with Windows NT 4.0 Beta 2 and has been available in every Microsoft operating system released since then. The original protocol available from Microsoft for VPNs, now available in version 2, is Point-to-Point Tunneling Protocol (PPTP). Two VPN tunneling protocols exist in Microsoft’s implementation of VPN.

MS-CHAP v2 Second, further improved version of MS-CHAP with server verification ■ĮAP Modular authentication capabilities that enable vendors to add new authentication methods ■ĮAP-TLS An EAP type that uses certificate-based modular authentication MS-CHAP Microsoft’s improved implementation of CHAP with error codes and capabilities to change password at logon ■ SPAP Clear-text username and reversible encrypted password ■ĬHAP Clear-text username and one-way hashed MD5 value in place of the password ■ The following list summarizes the authentication protocols used in Microsoft VPN technologies: ■ The various authentication protocols in use and supported by Windows Server 2003 vary in strength and features from PAP authentication with no encryption of password or user name to Microsoft Challenge Handshake Authentication Protocol version 2 (MS-CHAP v2), which provides encryption and user and system verification capabilities.

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