Sharing a DSL connection with Both Local and Remote Clients

You have a high-speed DSL connection (or cable modem connection, or T1, or whatever) that you want to use from everywhere in your local lan. You also want access to your local lan from a remote laptop. While you're at it, you also want the remote laptop to be able to access the Internet through your highspeed connection. What follows is a description of how to arrange a network like this. The description uses Windows NT on the gateway host, but I'm sure other operating systems could function in a similar manner. For that matter, you could start throwing together a Cisco router with a few WAN connection devices and get something similar. I'm trying to stick with a more common consumer configuration here.

In brief, this configuration provides:

Shared access to the Internet (via the DSL connection) from PCs on the LAN.
Access to the LAN from a remote PC.
Shared access to the Internet (via the DSL connection) from a remote PC.

Imagine the following configuration:

rras.gif (9927 bytes)

The network depicted consists of a LAN (hosts GatewayHost and LocalHost1), a remote laptop, and a DSL connection to the Internet. We are assuming that the GatewayHost is running NT Server, has Microsoft's "Routing and Remote Access Service" installed (available as a download from Microsoft's web site), and is running a NAT server (such as Sygate, NAT1000, etc). (According to Microsoft's web site, "Routing and Remote Access Service can be installed only on a computer running Windows NT Server.")

Capabilities provided by this configuration:

The Gateway host, via DSL modem and the NIC attached to it, has a standard 1-PC connection to the Internet.
The Gateway host, by running a NAT server, provides access to the Internet for PCs on the local LAN (e.g. Localhost1).
The LAN is protected from unfiltered Internet access by the Gateway host and its NAT server.
Other hosts on the Internet can access the Gateway host directly (subject to security) and can reach interior hosts as allowed/configured by the NAT server.
The remote laptop can access the local LAN as if directly connected (albit at a slower speed) by an Ethernet tap. Conversely, PCs on the local LAN can initiate connections to the remote laptop.
The remote laptop can access the Internet (through the Gateway host) as if directly connected to the DSL modem (albit at a slower speed). The remote laptop's access is not through the NAT server. Other hosts on the Internet can also reach the remote laptop, as long as the laptop is connected. The laptop's access is basically the same as if dialed into an ISP.

One obvious use for this configuration is for people who have a DSL connection and who also travel. If their DSL ISP does not provide dialup access, this configuration provides it for them. In addition, even if you have dialup ISP access, you may travel to a location not covered by a local access number for your ISP, in which case you are faced with either 800 number access charges (typically about .10 a minute) or long distance charges. Often times, while traveling, the long distance charges are at a higher rate than those on your home phone line. In the above configuration, it's easy to configure the RAS server on NT to provide call-back service. With call-back service, the Gateway host will call the remote laptop back, allowing the dialup session to be made from the home base (with the good telephone rates enjoyed by the home phone line). So for the same price, or even cheaper, of calling your ISP, you can get access to both the Internet and your local LAN from a remote laptop.

Requirements:

TBD.

Sygate, who produce a popular a NAT server, describe a 2nd method of providing both local LAN and remote client access to the shared DSL connection. The Sygate solution funnels both the local LAN and the remote client through the NAT server and doesn't require any additional IP addresses from the ISP. The Sygate solution is depicted below:

rras2.gif (9224 bytes)