Layer 2 Tunneling Protocol (L2TP) is supported by Nortel Networks and other vendors. L2TP combines the best features of the L2F and PPTP tunneling protocols. L2TP tunneling allows secure remote access to corporate networks across the public Internet. L2TP tunnels are generally established between a network access server (NAS) at the ISP and the gateway.
L2TP allows you to specify MS-CHAP, CHAP, or PAP authentication, enable compression, and assign DNS and WINS servers to the tunnel.
You can use IPSec transport-protected L2TP tunneling for both remote access traffic and branch office tunnel traffic. Windows 2000 can act as a peer in a branch office connection using L2TP/IPSec or IPSec tunnel mode. Also, Windows 2000 can act as a client using L2TP/IPSec. Authentication for L2TP/IPSec tunnels can be either shared secret or digital certificate. It also provides configuration support for both voluntary and compulsory L2TP/IPSec remote access connections. (Windows 2000 authentication must be digital certificate.)
The gateway supports IPSec transport mode to support the termination of Microsoft Windows 2000 L2TP/IPSec connections and to provide security for L2TP traffic for client-to-gateway connections and gateway-to-gateway connections.