• Authentication: The VPN server verifies the VPN client’s identity and
restricts VPN access to authorized users only (MS-CHAP and MS-CHAP v2).
The VPN server may also provide audit and accounting capabilities to
monitor who accessed which information and when.
• Tunneling: A technology that enables one network to send its data via
another network’s connections. Tunneling works by encapsulating a
network protocol within packets carried by another network. Tunneling is
also referred to as encapsulation (see
Section 2.3.1, “Protocol
Description”
) and is achieved by the GRE and PPP protocol.
• Encryption: To insure privacy, data transmission via the VPN over the
Internet is rendered unreadable to unauthorized clients through
encryption (MPPE).
• Compression: The process of reducing the amount of information
necessary to transmit data.
Authentication.
PPTP VPN servers use two authentication protocols:
• PAP: The Password Authentication Protocol is a simple authentication
protocol to authenticate a user with a Network Access Server. PAP sends
user names and passwords over the network in cleartext and is therefore
insecure.
• CHAP: Stands for Challenge Handshake Authentication Protocol and
functions as follows:
1. The PPTP VPN server sends a challenge to the requesting client.
2. The client uses this challenge and the password to calculate a response,
which is sent to the server.
3. The PPTP VPN server checks the provided response against its own
calculation of the expected response. If the received response matches,
the server acknowledges the authentication; if not, the connection is
terminated.
• PAP is not supported by the aXsGUARD Gatekeeper because it
is insecure. Only MS-CHAP is supported.
• VASCO recommends DIGIPASS authentication, as this is the
most secure option.
Tunneling.
A VPN uses an IP tunneling mechanism where the packet formats
and the addressing used by the VPN might be unrelated to the packet formats
and addressing which is used to route the tunneled packet across the Internet
(see
Section 2.5, “Routing Scenarios”
for more information about PPTP and
Routing). For this reason, PPTP uses the Generic Routing Encapsulation (GRE)
protocol. The GRE protocol is defined per
RFC-1701
,
1702
and
2784
and is
identified as IP Protocol 47. GRE is used to implement several categories of
encryption and network security. In its most basic form, GRE allows any
network-layer protocol (or in some cases, protocols from other layers, e.g.
Ethernet frames) to be encapsulated in any other network-layer protocol. In its
current form, GRE has been implemented in most UNIX network stacks, routers
and other network equipment and is widely supported.
Ecryption.
PPTP supports PPP-based data encryption mechanisms. The
Microsoft implementation of PPTP supports optional use of Microsoft Point-to-
Point Encryption (MPPE), based on the RSA/RC4 algorithm. 40 bit encryption is
supported, but highly insecure (see
Section 3.3, “General Configuration
© VASCO Data Security 2011
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Страница 6: ...List of Examples 3 1 Restricting access to two LAN servers VASCO Data Security 2011 5 ...
Страница 35: ...2 Select Set up a connection or network Figure 4 8 Windows Vista PPTP Setup VASCO Data Security 2011 34 ...
Страница 48: ...Figure 4 27 PPTP Status VASCO Data Security 2011 47 ...