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Communication Security: Remote Access and Messaging • Chapter 3 117

Remote Access VPN

A remote access VPN, known as a virtual private dial-up network (VPDN), differs
from a site-to-site VPN in that end users are responsible for establishing the VPN
tunnel between their workstation and their remote office.An alternative to con-
necting directly to the corporate VPN is connecting to an enterprise service
provider (ESP) that ultimately connects them to the corporate VPN.
In either case, users connect to the Internet or an ESP through a point of pres-
ence (POP) using their particular VPN client software. Once the tunnel is set up,
users are forced to authenticate with the VPN server, usually by two or three factor
authentication.

Figure 3.3 Client Workstation Establishes a VPN Tunnel to Remote Host

Internet

Client requests
connectivity

Internet

VPN / Firewall responds
upon valid authentication

Tunnel across the Internet

RADIUS

As noted in the discussion about 802.1x, users need a centralized entity to handle
authentication. Initially, RADIUS was created by Livingston Enterprises to handle
dial-in authentication.Then its usage broadened into wireless authentication and

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