The previous articles address configuration of the IP protocol for network adapters on a Linux computer. Linux can implement very complex routing using multiple network adapters, but most configurations utilize a pair of network adapters. These can be any combination from a pair of Ethernet adapters to an Ethernet adapter and a modem. This article will concentrate on the former, while the next article will address the latter. The routing software, or simply router, listens at a network adapter for messages, also called packets, addressed to it in the same way as the Apache web server, httpd, listens for Web-page requests.
Many services can use a single network adapter without a conflict.
Other computers on the network direct messages to the router. The other computers are setup to do this by setting the IP address of the router in the computer's default router or gateway setting. The router takes incoming messages and checks the destination IP address to determine where to forward the message. It uses routing tables to make this determination. The message may wind up being sent to another network segment or it may be forwarded yet again to another computer acting as a router.