A router is used to route data packets between two networks. The router reads the information in each packet to tell where the packet is going. If the packet is destined for an immediate network the router has access to, the router will strip the outer packet, readdress the packet to the proper ethernet address, and transmit the packet on that network. If the packet is destined for another network and must be sent to another router, the router will re-package the outer packet to be received by the next router and send the packet to the next router.
The section on routing at Network Routing explains the theory behind router operation and how routing tables are used to help determine packet destinations. Routing occurs at the network layer of the OSI model. Routers can connect networks with different architectures such as Token Ring and Ethernet. Although routers can transform information at the data link level, routers cannot transform information from one data format such as TCP/IP to another such as IPX/SPX. Routers do not send broadcast packets or corrupted packets. If the routing table does not indicate the proper address of a packet, the packet is discarded.