Multi-Homed Systems
Some computers need more than one network card. For example, if you have two subnets in your LAN that both need to connect to the same server, the server computer needs more than one network adapter. Although you can use a router to connect different subnets, it is probably cheaper to simply multi-home a server for a small network than to bother with the administrative overhead of configuring and maintaining a router.
In this case, the server can function both as a file or print server to both subnets and as a router. It is also possible, depending on the type of computer, to attach more than one network card to the same subnet. In any case, each network card must be set up with its own network address and host name. For example, a high-performance server might be used on an intranet to provide a WWW service and an FTP service to clients. If the server is capable of processing the requests at the required rate but the network adapter card is a limiting factor, you can install multiple cards and assign an address and host name for each service.
One popular reason for multi-homing a server today is to provide a hardware platform that can function as a proxy server for a network firewall. In this configuration, the proxy server application intercepts all traffic that passes between the two subnets to which it is connected, and acts as a go-between to enhance security on the network. The proxy server accepts service requests from one adapter and interacts with the service provider through the other adapter. The proxy server examines responses from the service and, if allowed, returns them to the requesting computer using the first network adapter.
| For more information about proxy servers, see Chapter 45, "Firewalls." |
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