
Configuring and Troubleshooting Bay Dial VPN Services
1-8 303509-A Rev 00
The following considerations apply only to Layer 2 (L2TP) tunnels:
• If the PC or router does not have built-in L2TP software capabilities, it dials
into a LAC, which provides a tunnel across the Internet to the corporate LNS.
This type of connection is the primary focus of this guide.
• If the PC or router is an L2TP client, that is, it has built-in L2TP capability,
the L2TP client software provides a tunnel through a network access server
across the Internet to the corporate LNS. A LAC is unnecessary with an L2TP
client.
The main difference between connecting an L2TP client and a nonclient is the
starting point of the tunnel. For an L2TP client, the tunnel begins at the PC or
router; for a non-L2TP client, the tunnel begins at the LAC. All tunnels end at the
LNS.
ISP Network Components for Layer 3 Tunnels
The devices that make up the Dial VPN service provider network can be all at the
same site or can be separated by several “hops” within the same network. A
network with Layer 3 Dial VPN tunnels can consist of a network access server
(NAS), a gateway router that serves as the tunnel end point, and a tunnel
management server.
Network Access Server (NAS)
A network access server (NAS) can be a Remote Access Concentrator
Model 8000 or a System 5000 chassis with one or more Model 5399 Remote
Access Concentrator modules. Each module is configured with a network address
belonging to the service provider’s address domain. The Remote Access
Concentrator 8000/5399 includes a dual WAN server, which can support both
analog calls and digital calls carried over ISDN. The NAS receives and processes
calls from remote nodes and routes data to remote nodes.
Note:
This guide uses the term network access server (NAS) to refer to the
device that performs network access functions, such as answering dial-in user
calls, authenticating tunnel users, building tunnels, and so on. In the Dial VPN
context, this device is usually a Remote Access Concentrator (RAC). Other
documents may refer to this same device as a remote access server (RAS).
Essentially, all three terms (NAS, RAS, and RAC) refer to functionally the
same device.
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