Panasonic NN46240-710 - Manual (Page 22)

1 L2TP troubleshooting
Nortel Secure Router 8000 Series
_________ Troubleshooting - VPN
1.1 L2TP overview
L2TP is a VPDN tunnel protocol. This protocol supports transmission in a tunnel that is
encapsulated by the PPP link and is applicable to remote access, such as remote user access to
the internal source of the enterprise.
1.1.1 Two typical L2TP tunnel modes
The tunnel modes of PPP frames, which are between the user and L2TP Network Server
(LNS), and between the user and L2TP Access Concentrator (LAC) clients (hosts running
L2TP), are shown in Figure 1-1.
Figure 1-1 Typical L2TP tunnel modes
LAC client
Internal server
Remote
system
Internal server
The methods of establishing a tunnel are as follows:
• NAS-initialized: Initiated by remote dial-up users. The remote system dials LAC through
the Public Switched Telephone Network (PSTN) or Integrated Services Digital Network
(ISDN). LAC sends a request to establish a tunnel connection to LNS through the
Internet. The addresses of the dial-up users are assigned by LNS. The agent on LAC or
LNS performs the authentication and accounting of remote dial-up users.
• Client-initialized: Initiated directly by LAC users who support L2TP. In this case, LAC
users can directly send a request to establish a tunnel connection to LNS, without the
need to pass through another LAC device. The addresses of the LAC users are assigned
by LNS.
1-2 Nortel Networks Inc. Issue 5.3 (19 January 2009)