Chapter 14 VPN
A connection that uses the Internet as a "transport medium" but is not publicly accessible is
referred to as a VPN (Virtual Private Network). Only authorised users have access to such
a VPN, which is seemingly also referred to as a VPN tunnel. Normally the data transported
over a VPN is encrypted.
A VPN allows field staff or staff working from home offices to access data on the company's
network. Subsidiaries can also connect to head office over VPN.
The connection partner is authenticated with a password, using preshared keys or certific-
ates.
With IPSec the data is encrypted using AES or 3DES, for example.
14.1 IPSec
IPSec enables secure connections to be set up between two locations (VPN). This enables
sensitive business data to be transferred via an unsecure medium such as the Internet.
The devices used function here as the endpoints of the VPN tunnel. IPSec involves a num-
ber of Internet Engineering Task Force (IETF) standards, which specify mechanisms for the
protection and authentication of IP packets. IPSec offers mechanisms for encrypting and
decrypting the data transferred in the IP packets. The IPSec implementation can also be
smoothly integrated in a Public Key Infrastructure (PKI, see
on page 69). IPSec
implementation achieves this firstly by using the Authentication Header (AH) protocol and
Encapsulated Security Payload (ESP) protocol and secondly through the use of crypto-
graphic key administration mechanisms like the Internet Key Exchange (IKE) protocol.
Additional IPv4 Traffic Filter
bintec elmeg gateways support two different methods of setting up IPSec connections:
• a method based on policies and
• a method based on routing.
The policy-based method uses data traffic filters to negotiate the IPSec phase 2 SAs. This
allows for a very "fine-grained" filter to be applied to the IP packet, even at the level of the
protocol and the port.
The routing-based method offers various advantages over the policy-based method, e.g.,
NAT/PAT within a tunnel, IPSec in combination with routing protocols and the creation of
VPN backup scenarios. With the routing-based method, the configured or dynamically
bintec elmeg GmbH
14 VPN
be.IP 4isdn
235
