VPN Concentrators
A VPN concentrator is a device that creates remote access for virtual private networks (VPNs) either for users logging in remotely or for a large site-to-site VPN. In contrast to standard remote-access connections, remote-access VPNs often allow higher data throughput and provide encryption. Cisco produces VPN concentrators that support anywhere from 100 users up to 10,000 simultaneous remote-access connections.
Encryption for a remote-access VPN through a concentrator is usually handled by Internet Protocol Security (IPSec) or by Secure Sockets Layer (SSL), and user authentication can be achieved via Microsoft’s Active Directory; Kerberos; Remote Authentication Dial In User Service (RADIUS); Rivest, Shamir, and Adleman (RSA); and digital certificates. Many VPN concentrators also have a built-in authentication server and allow ACLs to be implemented through them. In Figure 15.15, you can see where VPN concentrators are usually placed within a network setup.
