The procedures in this section assume that you (Web hosting reseller)
The procedures in this section assume that you have already set up a LAN, as described in Chapter 15. It is also assumed that you have an outgoing connection from your Red Hat Linux system to the Internet that all traffic between the computers on your LAN and the Internet can pass through. That outgoing connection may be dial-up or through another LAN card connected to a DSL modem or other LAN. This section describes two ways to set up the Red Hat Linux computer so clients on the LAN can access the Internet: As a router By configuring Red Hat Linux as a router, it can route IP packets from clients on the LAN to the Internet through the dial-up connection. As a proxy server You can configure Red Hat Linux as a proxy server. In this way, client computers on your LAN can access the Internet as though the connection were coming from the Linux computer. Setting Up Red Hat Linux as a Router There are several different ways to set up routing from your LAN to the Internet. You can have a dedicated router (such as the Cisco 675 ADSL router), or you can have a computer already connected to your LAN that will act as a router. This section describes how to use your Red Hat Linux computer as a router. A computer may have several network interfaces, such as a loopback, an Ethernet LAN, a direct line to another computer, or a dial-up interface. For a client computer to use a router to reach the Internet, it may have private IP addresses assigned to computers on the LAN, while the connection to a routing computer would act as the gateway to all other addresses. Here is a fairly simple example of a Red Hat Linux computer being used as a router between a LAN and the Internet: The Red Hat Linux system has at least two network interfaces: one to the office LAN and one to the Internet. The interface to the Internet may be a dial-up PPP connection or a higher-speed DSL or cable modem connection. Packets on the LAN that are not addressed to a known computer on the LAN are forwarded to the router (that is, the Red Hat Linux system acting as a router). So, each client identifies that Red Hat Linux system as the gateway system. The Red Hat Linux “router” firewall is set up to receive packets from the local LAN, then forwards those packets to its other interface (possibly a PPP connection to the Internet). If the LAN uses private IP addresses, the firewall is also configured to use IP masquerading. Tip You can set up a Linux computer as a dedicated router. The Linux Router Project (www.psychosis.com/linux-router) is a mini-distribution of Linux that fits on one 3.5-inch floppy disk. With it, you can maintain a router and terminal server more simply than with a full Linux system. This is a good way to make use of that old 486 in the closet. The following sections describe how to set up the Red Hat Linux router, as well as the client computers from your LAN (Red Hat Linux and MS Windows clients) that will use this router. Using Red Hat Linux as a router also provides an excellent opportunity to improve the security of your Internet connection by setting up a firewall to filter traffic and hide the identity of the computers on your LAN (IP masquerading).
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